About the guide

	This is a guide for Working Model. It has on-screen help, as well as projects for you to try.

Related Topics and Steps

At the end of each section and each project there are hot links to the next part. Any green text is hot — just click it if you want to go on.

Definitions

In text, you may find some underlined words. Clicking the underlined words gives you a definition or explanation.


About the Workshop projects

This guide contains six Workshop projects for you to try. All six appear in the Workshop topic, but they also appear individually within other topics — determined by what Working Model features they showcase.

In each Workshop project, you will be guided through creating a basic model. After creating the model, you will get instructions for improving it using features found in Working Model. Then, you will apply changes to the model to see how they affect the simulation.

Additionally, with each model, you will be given suggestions for further exploration on your own.


What's new with Working Model
What’s new with Working Model

	Working Model has some major improvements. Now you’ll find NURB-based geometry:  simulate collisions of curved geometry such as NURB-based cams/followers, and so on.  Dockable tool palettes:  Windows users can customize their work environments with simple drag and drop manipulations. Significantly improved performance:  Working Model runs from two to eight times faster for Windows 95 and Windows NT users.


Overview: Bouncing a ball

	In this project, you will bounce a ball on a table. To do this, you will make objects and change how the objects and workspace look. Then, you will change the ball’s material to see how it affects the simulation. To do this project, you will use the toolbar and the Window and View menus.  Steps 1. Create the ball and table. 2. Change the model’s appearance. 3. Change the ball’s properties.


Overview: Swinging a pendulum

	In this project, you will make a pendulum and watch how it swings. To do this, you will create two bodies and an object called a constraint. To enhance the simulation, you will track the pendulum’s position and add a time meter. With the meter to guide you, you can change  the pendulum to get it to swing back and forth in an exact time period. Steps 1. Create a pendulum. 2. Set tracking. 3. Add a time meter.


Overview: Launching a projectile

	In this project, you will make a simple projectile system.  You will add input controls. These will allow you to change the projectile’s velocity to get the ball, eventually, to land on a shelf. Additionally, you will re-define the model’s World to see what different environments do to the simulation.  Steps 1. Create a projectile and define the workspace. 2. Create and edit input controls. 3. Change the model’s world.


Overview: Controlling collisions

	In this project, you will create and control a collision between two billiard balls.  You will display velocity vectors and use meters so that you can monitor the collision during the simulation. Using data from the meters, you can control the collision. Steps 1. Create billiard balls and set the background. 2. Add velocity vectors to the model. 3. Add momentum meters to the model.


Overview: Sliding down an incline

	In this project, you will control the behavior of a box on a ramp. To do this, you will create the objects and analyze the contact forces between them. Additionally, you will add a force  to keep the box from sliding down the ramp. Steps 1. Create the box and incline. 2. Add vectors and edit mixed properties. 3. Measure the contact forces. 4. Apply external forces.


Overview: Tossing a ball

	In this project, you will throw a ball straight up towards the ceiling.  To do this, you will give the ball an initial velocity and see how gravity affects its motion. Additionally, you will control the duration of the simulation and create a graph to help you analyze the ball’s motion. Steps 1. Create a ball and set its initial velocity. 2. Add a pause control to the model. 3. Add a graph to quantify motion.


About bodies

With the basic geometric shapes available in the toolbar, you can create a variety of bodies to represent different objects.

Each body has parameters that define its behavior when you run a simulation. Initially, these parameters are set to default values. Once a body is created, you can change its properties, change its appearance, and attach constraints.


How do I create a body?

	You use a variety of shapes to represent bodies in your models. These shapes include circles, rectangles, squares, polygons, and curved polygons. You create bodies using tools in the toolbar.

To create a circle:

1.	Click the Circle tool in the toolbar.
2.	Click in the workspace area and drag diagonally to create a body.

To create a rectangle:

1.	Click the Rectangle tool in the toolbar.
2.	Click in the workspace area and drag diagonally to create a body.

To create a square:

1.	Click the Square tool in the toolbar.
2.	Click in the workspace area and drag diagonally to create a body.

To create a polygon or curved polygon:

1.	Click the Polygon tool or the Curved Polygon tool in the toolbar.
2.	Click the pointer in the workspace area to create the first vertex (corner) of the polygon. Continue clicking to create each of the other points of the polygon. End the polygon by clicking the starting point again, or by double-clicking the last point.
	Each body has parameters (properties) that define its behavior when you run a simulation. When you create a body, these parameters are set to default values. You can change them easily.  Once you create a body, you can attach constraints at precise locations on it. Related Topics How do I change body properties? How do I create a constraint?


How do I change body properties?

	Each object in the Working Model workspace behaves according to its defined characteristics and properties. You can change the properties of a body in the Properties window.
1.	Click a body to select it.
2.	Open the Window menu and choose Properties. or Double-click the object.
3.	Type new values in the x, y, or ø fields in the Properties window. The selected body will change its position. If you drag the body to re-position it in the workspace, you’ll see the values change in these fields.  The angle (ø) specifies the orientation of the body. When you change the value of ø, the body rotates with its geometric center fixed in the World frame.
4.	Type numerical values in the velocity fields to change the body’s initial velocity in the simulation.  The ø coordinate indicates the initial angular velocity of the object about its center of mass.
5.	Open the material pop-up menu and choose the substance that you want to simulate. When you change the material, many of the body’s properties are set to match the material. Once set, you can adjust the other properties if you need to. The values set are: density, mass, moment, the friction coefficients, elasticity, and charge.
	The Properties window always displays the properties of the selected body. Related Topics How do I create a body? How do I create a constraint? How do I rotate a body?


How do I change a body's appearance?
How do I change a body’s appearance?

	You can change the appearance of each body. By using color, adding tracking options, and labeling bodies, you can make your models easier to understand and more attractive. You change a body’s appearance using the Appearance window.
1.	Click a body to select it.
2.	Open the Window menu and choose Appearance.
3.	Press the two Frame palettes to change the body’s outline color and line width.
4.	Press the two Fill palettes to change the body’s interior color and pattern.
5.	Click the checkboxes to select tracking options. Track center of mass will leave a point at the body’s center. (Show center of mass will make the track more pronounced.) Track connect will leave connecting lines between the body’s center of mass as it moves. Track outline will leave a trace of the body’s outline. To activate the tracking feature, you must turn it on using the Tracking submenu in the World menu.
6.	Type a name for the body in the text box.
7.	Click the Show Name checkbox to put an X in it.  (If it is already checked, skip this step.)
	The Appearance window displays the appearance parameters for the selected body. Related Topics How do I anchor a body? How do I add pictures? How do I change body properties? How do I create a body?


How do I change a body's geometry?
How do I change a body’s geometry?

	You can edit the position, orientation, and dimensions (width, height, radius) of a body quickly in several ways.

To use the Coordinates bar:

1.	Click a body to select it.
2.	Click the field on the coordinates bar that you would like to change.
3.	Type the new value for that field, and press the Enter key.

To use the Geometry window:

1.	Click a body to select it.
2.	Open the Window menu and choose Geometry.
3.	Type a new value in the field that you want to change.
4.	Click the radio button next to x-offset if you want to change the Center of Mass (COM) for the selected body. Type the new values and press Enter. (Skip this step if you want to keep the default COM.)
5.	Select whether to display shape or world coordinates (if the selected body is a polygon).

To use input controls:

1.	Click a body to select it.
2.	Open the Define menu and choose New Control, then choose the type of geometric control you want from the submenu.
3.	Set the value that you want in the input control to change the body’s geometry.
	Now, you can change the geometry of any body in your model easily. Related Topics How do I create a body? How do I change body properties? How do I change a body’s appearance? How do I create a control?


How do I rotate a body?

	Once you have a body in your workspace you can rotate it using the Rotate tool.
1.	Click a body to select it.
2.	Click the Rotate tool in the toolbar.
3.	Drag the cursor after clicking where you want the center of rotation to be. The center of rotation can be a COM of an object, the 0,0 coordinate, or a point you have placed on a body.
	Now you can orient the bodies in your model at any angle. Related Topics How do I create a body? How do I build complex objects?


How do I anchor a body?

	You can connect bodies to the background so they don’t move in the simulation. Some bodies need to be anchored, such as a table or a ceiling. You use the Anchor tool to keep a body from moving.
1.	Click the Anchor tool in the toolbar.
2.	Click inside a body with the Anchor tool to anchor it to the background. The body will stay in that position until you move it to a different position or remove the anchor.
	Anchors keep your bodies in place. You can use other constraints on bodies as well. Also, if you don’t like seeing the anchors in your model, you can hide them — like other constraints. Related Topics How do I create a constraint? How do I control collisions? How do I hide a constraint?


How do I delete an anchor?

	Anchored bodies are connected to the background; therefore, they don’t move during a simulation.  When editing a model, you may want to remove an anchor from a body that you now want to move. You use the Delete key to remove anchors.
1.	Select the anchor mark in a body, and press the Delete key. The body is now free to move.
	Anchors keep your bodies in place. You can can add and delete anchors as needed. Related Topics How do I create a constraint? How do I anchor a body?


How do I change a body's COM?
How do I change a body’s COM?

	By default, all bodies in Working Model have their center of mass (COM) at their geometric center. In Auto mode, the COM is recalculated automatically whenever the body is reshaped, so that the COM coincides with the geometric center. A body’s center of mass can be moved by modifying the x- and y-offset fields in its Geometry window.
1.	Click a body to select it.
2.	Open the Window menu and choose Geometry.
3.	Click the radio button next to x-offset.
4.	Type the values for the new center of mass.
	Now, you can change the center of mass for any body in your model. Related Topics How do I create a body? How do I change body properties? How do I change a body’s appearance? How do I change a body’s geometry?


How do I control collisions?

	By default, all bodies in Working Model that are not connected can collide with each other. When objects do not collide, they penetrate one another.  You can change the default by setting Do Not Collide in the Object menu.
1.	Select the two bodies that you don’t want to collide. To select two or more bodies, press the Shift key while you click each body.
2.	Open the Object menu and choose Do Not Collide. A checkmark will appear next to Do Not Collide in the menu.
	The collision property is always between pairs of bodies. Your simulation may have some pairs that collide with each other and others that don’t. Related Topics How do I create a constraint? How do I control a simulation? How do I minimize collisions? How do I prevent rebounding inelastic collisions?


Why can't I select points in an object?
Why can’t I select points in an object?

Points are always in the graphics layer below the layer of other objects. When the fill pattern of an object is transparent, you can see the points that are actually covered by the objects, but you cannot move the mouse over those points to select them by clicking.

You can select the points by dragging to select them. Start the dragging from outside the object covering the points, and enclose the desired points within the selection. You will not select the object unless it is completely within the boundaries of the selection rectangle.

Also, you can select a point by double-clicking the object to open its Properties window, then choosing the point from the pop-up menu at the top of the window.


Why can't I highlight points?
Why can’t I highlight points?

If you select multiple overlapping points, they do not appear highlighted because Working Model uses a special algorithm to draw selection highlighting.

Multiple points may overlap if you split a pin joint. By doing this, you get two points that lie directly on top of each other. Each point will be connected to a different mass object.

You can verify that multiple points are selected by choosing Properties from the Window menu. The top menu will will show "mixed selection".


acceleration

Acceleration is the rate at which velocity is changing.  The change may be magnitude, direction or both.


anchor

	You use the anchor tool to anchor bodies to the background so they don’t move when you run a simulation. Related Topics How do I anchor a body? How do I delete an anchor?


angular velocity

When a rigid body rotates, the position angle changes with time.  Angular velocity refers to the rate of change of the angle with time measured in radians per second.


Appearance window

The Appearance window allows you to change how objects look in your simulations. In the Appearance window you can change an object's color, change its name, show or hide constraints, and set tracking options.

To use the Appearance window, select the object. Then open the Window menu and choose Appearance.

Related Topics

How do I change a body’s appearance?

How do I change a control’s appearance?

How do I modify a meter?


center of mass

When determining how an object will react to forces, scientists make some basic assumptions. The center of mass assumes that a body will react as if its entire mass is concentrated at its geometric center.

In Working Model, by default, all bodies are created with the center of mass (COM) at the geometric center of the object. You can change an object’s COM from its geometric center using the Geometry window, which you open from the Window menu.

Related Topics

How do I change a body’s COM?


charge

The charge on a body determines how it will behave in an electrostatic field. This will only affect the simulation when the Electrostatics feature is turned on in the World menu.

In Working Model, the electric charge is lumped at the center of mass (COM) for each body.


circle

	You use the Circle tool to make circular bodies. Related Topics How do I create a body?


COM

When determining how an object will react to forces, scientists make some basic assumptions. The center of mass assumes that a body will react as if its entire mass is concentrated at its geometric center.

In Working Model, by default, all bodies are created with the center of mass (COM) at the geometric center of the object. You can change an object’s COM from its geometric center using the Geometry window, which you open from the Window menu.

Related Topics

How do I change a body’s COM?


curved polygon

	You use the Curved Polygon tool to create free-form, closed bodies with curved sides. Related Topics How do I create a body?


density

Density is the property of a substance equal to the mass divided by the volume; commonly thought of as the "lightness" or "heaviness" of a substance.

When you create an object, it initially has a density of 1.0 g per cubic cm. This is equal to the density of water. This means that, at least initially, larger objects are heavier than smaller objects because they have the same density.

You change the density of an object by specifying a different material for the body in the Properties window.

Related Topics

How do I change body properties?


elasticity

Elasticity is the property of a body or material by which it experiences a change in shape when a deforming force acts on it, and by which it returns to its original shape when the deforming force is removed.

In Working Model, elasticity is actually a property of collisions. In an elastic collision (elasticity = 1), the velocities of the bodies stay the same except that they are in the opposite direction. In an inelastic collision (elasticity = 0), the bodies stick together.

If the two bodies that collide have different elasticity values, the lower one is used to define the collision.

Related Topics

How do I change body properties?

How do I change constraint properties?


energy

Energy is the property of an object or a system which enables it to do work.


friction

Friction is the force that acts to resist the relative motion (or attempted motion) of objects or materials that are in contact.

In Working Model, two types of friction are considered in a simulation: static and kinetic friction. If two objects are in contact and not moving, the simulation uses the static friction value. If the objects are moving, the kinetic friction value is used.

If the two objects in contact have different friction values, the simulation uses the lower value of the two.

Related Topics

How do I change body properties?


geometric center

The center of a circle is where two radii cross. The geometric center of a rectangle (or square) is where the two diagonals cross. The geometric center of a polygon is a complex calculation based on the vertices.


Geometry window

The Geometry window allows you to adjust the size of a body that you have created already. You can also change the center of mass from the default (geometric) center.

To use the Geometry window, select the object. Then open the Window menu and choose Geometry.

Related Topics

How do I change a body’s COM?

How do I change a body’s geometry?


initial position/orientation

The initial position and orientation of a body can be changed by dragging the body on the screen.

To rotate a body, use the Rotator tool.

Also, you can type numerical values directly into fields on the Coordinates bar or the Properties window:

x (horizontal value)

y (vertical value)

ø (angle of rotation)

Related Topics

How do I change body properties?

How do I rotate a body?


initial velocity

You can use the Properties window to specify the initial velocity of the center of mass (COM) of a body.

When you begin your simulation, the initial velocity is the speed at which the body starts to travel before other forces (like gravity) start acting on it.

Related Topics

How do I change body properties?

How do I avoid inconsistent initial velocities?


mass

A body’s mass is the amount of material that it has. This determines how the body will react to forces applied to it.

In Working Model, bodies have mass; therefore, bodies are called mass objects. Constraints and points on bodies do not have mass.


mass object

In Working Model, bodies have mass; therefore, bodies are referred to as mass objects. Constraints and points on bodies do not have mass.


material

You can set many of a body’s properties quickly to a specific type of material. The standard materials available in the Properties window include: rubber, rock, plastic, ice, clay, wood, and steel. The "standard" choice in the materials pop-up menu has the properties of water.

Related Topics

How do I change body properties?


moment

By default, a new body is two-dimensional and its mass is uniformly distributed throughout it. Working Model uses these assumptions to assign a moment of inertia for the body.

In the Properties window, you can change the moment of inertia by having the mass distributed at the edges (for example, a shell) or throughout the body in three dimensions (for example, a sphere). Also, you can type a specific value for a body’s moment of inertia.

Related Topics

How do I change body properties?


momentum

Momentum is the product of the mass and the velocity of an object.


polygon

	You use the Polygon tool to make many-sided bodies that have straight sides. Related Topics How do I create a body?


Properties window

The Properties window allows you to change the properties of the different Working Model objects.

If the object is a body (or mass object), you can change things like: density, mass, initial velocity, and initial position. If the object is a constraint, you can change constraint properties like: length, the forces it applies, and elasticiy. If the object is a control,  you can change the type of control and minimum and maximum values. For meters, you can change labels, equations, and minimum and maximum values.

To use the Properties window, select the object. Then open the Window menu and choose Properties.

Related Topics

How do I change body properties?

How do I change constraint properties?

How do I change a control’s properties?


rectangle

	You use the Rectangle tool to make rectangular bodies easily. Related Topics How do I create a body?


square

	You use the Square tool to make square bodies easily.  Related Topics How do I create a body?


Toolbar

The toolbar appears along the left-hand side of a Working Model window. It contains all the tools you need for making and working with your models.

At the top, are the Run/Stop and Reset buttons for controlling your simulations. Then the tools for working with your model — for adding text, rotating objects, and dragging objects. Below these are the tools for creating bodies — circles, rectangles, and polygons — and the Anchor tool. Then are the tools for creating constraints — like ropes, springs, rods, joints, and motors.


velocity

The velocity of an object is the speed together with the direction of the motion.


weight

Weight is the force on a body of matter caused by the gravitational attraction of another body.


About constraints

In Working Model, a constraint applies a force (or torque) to bodies at one or more points. Unlike bodies, constraints do not have mass or volume.

Working Model has many different types of constraints for you to use in your simulations (for example: springs, ropes, rods, pulleys, and gears). You create constraints using the various constraint tools in the toolbar.


How do I create a constraint?

	Working Model has many different types of constraints for you to use in your simulations. You create constraints using the various constraint tools in the toolbar.

Ropes, Springs, Rods, and Separators

Ropes, springs, rods, and separators are similar types of constraints, called linear constraints. These constraints apply a linear force at the attachment points.

To create a rope:

1.	Click the Rope tool in the toolbar.
2.	Click where you want to have the first endpoint, then click where you want the second endpoint.

To create a spring:

1.	Click the Spring tool in the toolbar.
2.	Click where you want to have the first endpoint, then click where you want the second endpoint.

To create a rod:

1.	Click the Rod tool in the toolbar.
2.	Click where you want to have the first endpoint, then click where you want the second endpoint.

To create a separator:

1.	Click the Separator tool in the toolbar.
2.	Click where you want to have the first endpoint, then click where you want the second endpoint.

Dampers, Damped Springs, and Actuators

Dampers, damped springs, and actuators are types of linear constraints. These constraints apply a linear force at the attachment points.

To create a damper:

1.	Click the Damper tool in the toolbar.
2.	Click where you want to have the first endpoint, then click where you want the second endpoint.

To create a damped spring:

1.	Click the Damped Spring tool in the toolbar.
2.	Click where you want to have the first endpoint, then click where you want the second endpoint.

To create a actuator:

1.	Click the Actuator tool in the toolbar.
2.	Click where you want to have the first endpoint, then click where you want the second endpoint.

Motors, Rotational Springs, and Rotational Dampers

Motors, rotational springs, and rotational dampers are types of rotational constraints. This means that they apply a rotational force (or torque) at the attachment point.

To create a motor:

1.	Click the Motor tool in the toolbar.
2.	Click where you want to make the constraint.

To create a rotational spring:

1.	Click the Rotational Spring tool in the toolbar.
2.	Click where you want to make the constraint.

To create a rotational damper:

1.	Click the Rotational Damper tool in the toolbar.
2.	Click where you want to make the constraint.
	Once you create a constraint, you can change its properties. Related Topics How do I change constraint properties? How do I find constraint connections? How do I delete a constraint? How do I hide a constraint?


How do I create a joint?

	You can create several types of joints. Pin joints allow two bodies to rotate while making them overlap. Rigid joints lock two bodies together. Slot joints align a point on one body with a slot on another (or on the background). The slot can be either straight or curved.  You should have the bodies you want to join already in your model. You can join a body to the background, also.

To create a pin joint:

1.	Overlap the bodies that the joint will connect together.
2.	Click the Pin Joint tool in the toolbar.
3.	Click the overlapping bodies where you want to have the joint placed. If there are several overlapping bodies, only the two top bodies will be joined together. The Coordinates bar shows the x-y values for the Base Point (point on the second layer or background) and for the Top Point (point on the top layer).

To create a rigid joint:

1.	Overlap the bodies that the joint will connect together.
2.	Click the Rigid Joint tool in the toolbar.
3.	Click the overlapping bodies where you want to have the joint placed. If there are several overlapping bodies, only the two top bodies will be joined together. The Coordinates bar shows the x-y values for the Base Point (point on the second layer or background) and for the Top Point (point on the top layer).

To create a straight slot joint:

1.	Overlap the bodies that the slot joint will connect together. Be aware that the slot will be on the body (or background) underneath.
2.	Click one of the Straight Joint tools in the toolbar. You can create pin- or keyed joints that are vertical or horizontal. The pin-slot joint (with the round end) allows rotation along the slot. The keyed-slot joint (with the square end) eliminates any rotational movement.
3.	Click the overlapping bodies where you want to have the joint placed.  You can put a slot on the background, also. The top two bodies will be joined. The slot element will attach to the second body from the top or the background if only one body lies under the pointer. The Coordinates bar shows the x-y values for the Base Point (point on the second layer or background) and for the Top Point (point on the top layer).

To create a curved slot joint:

1.	Click the Curved Slot Joint tool in the toolbar.
2.	Click the body, which will move in the slot, at the point where you want it to be joined. Click as many control points as you like to create the slot; then, double-click the last control point to finish the slot. The slot pin will be attached to the body at the first point. The first point also becomes the first control point of the curved slot. Usually, the slot will be connected to the background.
	Once you create a joint, you can change its properties. Related Topics How do I change constraint properties? How do I find constraint connections? How do I break a joint apart?


How do I build a joint from separate pieces?

	Instead of using the Joint tool in the toolbar, you can construct a joint using basic pieces, then use the Join tool to bring everything together. You can build all types of joints from scratch. You should have the bodies that you want to join together in your workspace.

To build a pin or rigid joint:

1.	Use one of the Point tools to create points on each of the two bodies or one body and the background. Use the Square Point tool for a rigid joint or the Round Point tool for a pin joint.
2.	Press the Shift key as you select both points.
3.	Click the Join button in the toolbar. The bodies move, so the points overlap.

To build a slot joint:

1.	Use one of the Point tools to create a point on one of the two bodies. Use the Square Point tool for a keyed slot joint and the Round Point tool for a pinned slot joint.
2.	Click the Slot tool you want in the toolbar.   You can only make a keyed slot joint by joining a square point and a straight slot.
3.	To create a straight slot joint, click the other body (or the background) where you want the slot to be. or To create a curved slot joint, click several times along the path that you want the slot to take.
4.	Press the Shift key as you select both the point and the slot.
5.	Click the Join button in the toolbar. The bodies move, so the slot and point overlap.
	Now, you can create complex joints using basic elements. Related Topics How do I create a joint? How do I change constraint properties? How do I delete a constraint? How do I break a joint apart?


How do I break a joint apart?

	You can break a joint apart into its basic parts. Elements that are split "remember" that they were once joined, so it is easy to take apart pieces of a mechanism and then reassemble them.  You use the Split button in the toolbar to break a joint apart. You can use the Split  button with other constraints, too.
1.	Select the joint that you want to break apart.
2.	Click Split in the toolbar.
	When you’ve split a joint, the "pin" is removed. You can then move the individual bodies. Split elements "remember" that they were once joined, so it is easy to take apart a joint and reassemble it using the Split and Join buttons.  Related Topics How do I create a joint? How do I build a joint from separate pieces? How do I delete a constraint?


How do I create a pulley?

	Pulley systems have multiple points along with the two endpoints. You can attach each point in a pulley to the background or to a body. During a simulation, the total length of the rope remains the same, but the length between the endpoints and their adjacent points varies. You make a pulley with the Pulley tool in the toolbar. You should have at least one body (or more) to connect to the pulley.
1.	Click the Pulley tool in the toolbar.
2.	Click the Pulley tool on a body to make the starting point of the pulley. Continue clicking to create each of the other points in the pulley. Double-click the last point or press any key to complete the pulley.
	Once you create a pulley, you can change its properties. Related Topics How do I change constraint properties? How do I find constraint connections? How do I hide a constraint? How do I delete a constraint?


How do I create gears?

	Usually, gears have at least two circular bodies with teeth. These bodies touch and their rotations depend upon each other. You create gears using the Gear tool in the toolbar.
1.	Create two bodies in the workspace that will be constrained as gears and attach one of them to the background with a pin joint. Usually, these two bodies will be two circles in contact with each other.
2.	Click the Gear tool in the toolbar.
3.	Click the first body and drag to the second body.
	Once you create a set of gears, you can change the properties. Related Topics How do I change constraint properties? How do I find constraint connections? How do I hide a constraint? How do I delete a constraint?


How do I change constraint properties?

	Once you have created a constraint, you can use its Properties window to change its values.
1.	Click the contraint whose properties you want to change.
2.	Open the Window menu and choose Properties. or Double-click the object.
3.	Make your changes in the Properties window for the selected constraint. Each constraint has different properties that appear in its Properties window. See the definition for each constraint for information about the properties for it. For more detailed information, see Constraints in the User’s Manual.
	Now that you’ve customized your model’s constraints, you may want to test them. Related Topics How do I find constraint connections? How do I control collisions? How do I control a simulation?


How do I delete a constraint?

	It’s easy to delete any constraint that you no longer want in your model. You simply use the Delete key.
1.	Select the contraint that you want to delete.
2.	Open the Edit menu and choose Cut. Shortcut: Ctrl-X or Press Delete.
	Once you delete a constraint, you can replace it with another one.  Related Topics How do I create a constraint? How do I create a joint? How do I create a pulley? How do I create gears?


How do I hide a constraint?

	You can show or hide constraints (and anchors) selectively using the Appearance window. All constraints function whether they are hidden or showing.  You might want to hide constraints: to avoid a long slot cutting across your simulation screen. to make the model look more realistic.
1.	Select the constraint or anchor that you want to hide.
2.	Open the Window menu and choose Appearance.
3.	Click the Show checkbox to remove the X from it.  (If it is already clear, skip this step.)
	Now, you can show or hide constraints and anchors selectively. Related Topics How do I anchor a body? How do I delete an anchor? How do I create a constraint? How do I delete a constraint?


How do I find constraint connections?

	When your model gets complicated, it’s easy to lose sight of how bodies and constraints are connected. There is an easy way for you to find connections through the Properties window.
1.	Click the object for which you want to find associated connections. The object can be a constraint, a point element, slot element, or a body.
2.	Open the Window menu and choose Properties. or Double-click the object.
3.	Open the Selection pop-up menu at the top of the Properties window. Objects that are in bold type are attached to or closely associated with the selected object. For example, if you select a point, the pop-up menu shows the constraint that contains that point and the body to which the point is attached.
	Now that you know where all the connections are, you may want to run a simulation to see how they all work together. Related Topics How do I change constraint properties? How do I control a simulation?


Why can't I drag a point or a constraint?
Why can’t I drag a point or a constraint?

If you cannot drag a point or constraint, the Lock Points feature in the View menu may be on. Lock Points prevents points from moving relative to their mass objects.

Use the Lock Points feature when you edit complex linked figures or mechanisms. This feature prevents you from inadvertently changing the geometry or offset of a joint by dragging a point.


actuator

	An actuator is a multipurpose constraint that exerts whatever force necessary to maintain its constraint specifications. There are four types of actuators: force (the default), length, velocity, and acceleration actuators. You use the Actuator tool to make actuators in your model. You select the type of actuator and determine the constraint specifications in the Properties window. See Constraints in the User’s Manual for more details about actuators. Related Topics How do I create a constraint? How do I change constraint properties? How do I find constraint connections? How do I delete a constraint?


constraint

In Working Model, a constraint is an object that applies forces or torques to bodies at one or more  points. Unlike bodies, constraints do not have mass or volume. Also, they do not collide with themselves or with bodies.

A constraint is attached to one or more bodies (or the background). Each constraint has a specific definition of how it applies the force (or torque) to the body at its attachment point.

Related Topics

How do I create a constraint?

How do I change constraint properties?

How do I find constraint connections?

How do I delete a constraint?


damped spring

	A damped spring is a combination of a spring and a damper. The force exerted by a damped spring is equal to the sum of the forces applied by the spring and the damper components. For example, you can use a damped spring to simulate a car’s McPherson strut (a shock absorber with a coiled spring wrapped around it). You use the Damped Spring tool to make damped springs. In the Properties window, you can change the spring constant, the rest length of the spring, and the damping constant. See Constraints in the User’s Manual for more details about damped springs. Related Topics How do I create a constraint? How do I change constraint properties? How do I find constraint connections? How do I delete a constraint?


damper

	A damper exerts a force that depends on the difference in the velocities of its two endpoints. It applies no force if the endpoints have the same velocity. For example, you can use a damper to simulate the shock absorber in a car. In the Properties window, you can change the damper constant and the damper type. A damper with a high damper constant resists motion more than one with a low damper constant. See Constraints in the User’s Manual for more details about dampers. Related Topics How do I create a constraint? How do I change constraint properties? How do I find constraint connections? How do I delete a constraint?


force

	A force is a push or a pull on an object that causes motion. Forces have direction, so they are vector quantities. Forces on an object can be added together for you to determine the overall motion — that’s what Working Model does when it simulates a model. In Working Model, you make individual forces using the Force tool. Unlike most other constraints, a force has only one point, and it applies the specified force at that point. A force must be attached to a body to have any affect in simulations.  In the Properties window, you can change the components of the force vector and specify whether the force will rotate with the body. Related Topics How do I apply a force or torque? How do I change a force or torque? How do I delete a force or torque?


gears

	The Gear tool provides a constraint between two bodies so that their rotations are dependent on each other. By default, the gears are external gears — the two bodies touch and have gear teeth on their outer edges.
	This picture shows a typical use of gears in Working Model, where two disks of different radii are in contact.  One disk is driven by a motor, where the other is attached to the background with a pin joint.  In this case, the gear ratio is computed as the ratio of the two radii.
	You use the Gear tool to make two bodies into gears. Gears also have a built-in rod that can be useful when you are simulating planetary gears.  In the Properties window, you can change the gear ratio, whether the rod is active, and whether there is an internal gear. See Constraints in the User’s Manual for more details about gears. Related Topics How do I create gears? How do I change constraint properties? How do I find constraint connections? How do I delete a constraint?


joint

Joints are where two bodies (or one body and the background) are joined together. Some joints (like pin and slot joints) allow the bodies to move. Other joints (like rigid joints) don’t.

In the Properties window, you can change the placement of the joints on the bodies.

See Constraints in the User’s Manual for more details about joints.

Related Topics

How do I create a joint?

How do I build a joint from separate pieces?

How do I break a joint apart?


motor

	A motor is a multipurpose constraint that exerts the torque necessary to maintain a specified rotational force between the bodies.  A motor has two overlapping points and a built-in pin joint. There are four types of motors available: torque, rotation, velocity, and acceleration motors. You specify which type of motor you want in the Properties window.  See Constraints in the User’s Manual for more detail about motors.  Related Topics How do I create a constraint? How do I change constraint properties? How do I find constraint connections? How do I delete a constraint?


pin joint

	Pin joints allow rotation while forcing the points on two different bodies to overlap.  In the Properties window, you can change the placement of the joints on the bodies.   Related Topics How do I create a joint? How do I build a joint from separate pieces? How do I break a joint apart?


point

	A point element is one of the "building blocks" for making joints. Related Topics How do I build a joint from separate pieces? How do I break a joint apart?


pulley

	Pulleys behave like a single rope going through multiple fixed points and having two endpoints. The total length of the rope is fixed, but the length between adjacent points can vary and the force applied between the points is equal. You use the Pulley tool to connect bodies to a pulley. In the Properties window, you can change the total length, the lengths between each point, and the elasticity of the pulley system.  See Constraints in the User’s Manual for more details about pulleys. Related Topics How do I create a pulley? How do I change constraint properties? How do I find constraint connections? How do I delete a constraint?


rigid joint

	Rigid joints lock two bodies together. In the Properties window, you can change the placement of the joints on the bodies, and you can specify whether the joint is optimized or measurable.  Related Topics How do I create a joint? How do I build a joint from separate pieces? How do I break a joint apart?


rod

	A rod applies forces at its endpoints to maintain a fixed length.  You use the Rod tool to put a rod between two bodies. In the Properties window, you can change the the current length of the rod. If you change the length, the rod will be changed immediately and the rest of the model will be changed to accommodate that value.  See Constraints in the User’s Manual for more details about rods. Related Topics How do I create a constraint? How do I change constraint properties? How do I find constraint connections? How do I delete a constraint?


rope

	A rope limits the distance between two objects. It applies no force at all when the rope is slack, but the maximum force when it is taut. When a rope goes from being slack to being taut quickly, a "collision" occurs. The elasticity property determines how "bouncy" this collision will be. You use the Rope tool to connect two bodies with a rope. You can change the rope’s length in the Properties window. See Constraints in the User’s Manual for more details about ropes. Related Topics How do I create a constraint? How do I change constraint properties? How do I find constraint connections? How do I delete a constraint?


rotational damper

	Rotational dampers exert a torque that depends on the difference in angular velocities of the two bodies attached to the endpoints. For example, you can use a rotational damper to simulate a pin joint that has friction. You use the Rotational Damper tool to make a rotational damper in your model. A rotational damper has two overlapping points and a built-in pin joint. In the Properties window, you can change the damper constant, K, and the damper type.  See Constraints in the User’s Manual for more details about rotational dampers. Related Topics How do I create a constraint? How do I change constraint properties? How do I find constraint connections? How do I delete a constraint?


rotational spring

	Rotational springs exert a torque that depends on the difference in rotations of the two bodies attached to the endpoints. For example, a rotational spring can simulate a coil spring. You use the Rotational Spring tool to put a rotational spring in your model. A rotational spring has two overlapping points and a built-in pin joint. In the Properties window, you can change the spring constant and the spring type.   See Constraints in the User’s Manual for more details about rotational springs. Related Topics How do I create a constraint? How do I change constraint properties? How do I find constraint connections? How do I delete a constraint?


separator

	Separators behave like ropes, except that they act in the opposite direction. A separator prevents its endpoints from being less than a certain distance apart.  Unlike a rope, a separator applies no force at all when the distance between the endpoints is greater than the specified distance. You use the Separator tool to put a separator between two bodies. You can change a separator’s length, current length, and elasticity in its Properties window. See Constraints in the User’s Manual for more details about separators. Related Topics How do I create a constraint? How do I change constraint properties? How do I find constraint connections? How do I delete a constraint?


slot

	Slots are basic "building blocks" for making slot joints.  The slot element tools are used in conjunction with the point elements to form slot joints.  For example, you can attach a slot element to the background, attach a point element to a body, and join the two elements to form a slot joint." Related Topics How do I build a joint from separate pieces? How do I break a joint apart?


slot joint

	The slot joint tools are used to create various types of slot joints.  The "pinned" slot joint allows one body to "slide and rotate" with respect to the other.  A "keyed" allows one body to slide but not rotate with respect to the other. Related Topics How do I build a joint from separate pieces? How do I break a joint apart?


spring

	A spring exerts a force that depends on the distance between its two endpoints. It applies no force at all when the distance is equal to the rest length of the spring. The rest length is the length when the spring is neither stretched nor compressed. You use the Spring tool to put springs in your model. In the Properties window, you can change the spring constant, the rest length of the spring, and the spring type.   See Constraints in the User’s Manual for more details about springs. Related Topics How do I create a constraint? How do I change constraint properties? How do I find constraint connections? How do I delete a constraint?


torque

	A torque is a rotational force — a push or pull on a body to make it rotate about a center. Working Model has a special constraint, made with the Torque tool, to apply rotational forces in your models. It works on single bodies.  In the Properties window, you can change the value of the torque applied to the body. Positive torque is defined as counterclockwise. Related Topics How do I apply a force or torque? How do I change a force or torque? How do I delete a force or torque?


About forces and vectors

A force has one endpoint that indicates where the force is applied. You can define a force in Cartesian (x and y) or polar (rotation and magnitude) coordinates. The direction of a force can be specified either in relation to a body or in relation to the background.

A vector, placed on points and bodies, graphically represents velocity, acceleration, and force properties. To change the on-screen length of the vector without changing the physical magnitude of the force, use the Vector Length command in the Define menu.


How do I apply a force or torque?

	Forces and torques are special types of constraints in Working Model. Each has only one point, called the point of application, where it contacts a body. To apply a force (or torque) to a body, use the Force (or Torque) tool in the toolbar.

To apply a force:

1.	Click the Force tool in the toolbar.
2.	Click on a body in the location where you want the torque applied. The Coordinates bar shows where the force is applied (in x-y values) and the x and y components of the force.

To apply a torque:

1.	Click the Torque tool in the toolbar.
2.	Click on a body in the location you want the force applied. The Coordinates bar shows where the torque is applied (in x-y values) and the torque’s magnitude.
	Once you have added a force or torque to your model, you can change it. If you want to have forces (or torques) applied in a more specified way, you may want to use a constraint. Related Topics How do I change a force or torque? How do I delete a force or torque? How do I create a constraint?


How do I delete a force or torque?

	If you change your mind about forces or torques you added to your model, you can delete them easily with the Delete key.
1.	Select the force (or torque).
2.	Open the Edit menu and choose Cut. Shortcut: Ctrl-X  or  Press the Delete key.
	After you delete a force or torque, you may want to add another type of constraint to your model. Related Topics How do I create a constraint? How do I apply a force or torque?


How do I change a force or torque?

	Once you have created a force or torque, you can change its properties easily in the Properties window.

To change a force’s properties:

1.	Click the force to select it.
2.	Open the Window menu and choose Properties. or Double-click the object.
3.	Change the force values, the force vector values, or whether the force rotates with the body.

To change a torque’s properties:

1.	Click the torque to select it.
2.	Open the Window menu and choose Properties. or Double-click the object.
3.	Change the magnitude of the selected torque in the Properties window. Positive torque is defined as rotating in a counterclockwise direction.
	Now that you know how to change the forces and torques in your model, you can add and delete them as you need for your model. Related Topics How do I apply a force or torque? How do I delete a force or torque? How do I create a constraint?


How do I display vectors?

	You can graphically represent velocity, acceleration, and force properties by displaying vectors. You use the Vectors submenu of the Define menu to display vectors. You should have at least one body in your model on which you want to show vectors.
1.	Click a body to select it.  or Press the Shift key as you click more than one body.
2.	Open the Define menu and choose Vectors, then choose the type of vector that you want from the submenu. The Vectors submenu lists all the possible vectors that can be displayed for the selected object(s). If more than one object is selected, and the currently displayed vectors for the bodies do not match, a "-" will appear next to the vector type, signifying that a mixed selection exists. You can have more than one type of vector showing at a time.
	The vectors will be displayed the next time you run the simulation. Related Topics How do I adjust the length of a vector? How do I turn off vectors?


How do I turn off vectors?

	Once you have vectors displayed in your simulation, you can turn them off if you no longer want to see them. You use the No Vectors command in the Define menu to get rid of unwanted vectors.
1.	Click a body to select it.  or Press the Shift key as you click more than one body.
2.	Open the Define menu and choose No Vectors.
	You can display or hide vectors in your simulations as you wish. Instead of turning off vectors, you may want to just change their length. Related Topics How do I display vectors? How do I adjust the length of a vector?


How do I adjust the length of a vector?

	The length of a vector is based on its magnitude and a scale factor. Depending on the property a vector displays, it may be too long or too short to see its value. You can adjust the scale factor for vectors with the Vector Lengths command in the Define menu.
1.	Open the Define menu and choose Vector Lengths.
2.	Use the sliders to adjust vector lengths for velocity, force, and acceleration vectors. or Type a scale factor.
3.	Click OK.
	Now, you can scale the length of vectors in your model to fit within your workspace view.  Related Topics How do I display vectors? How do I turn off vectors?


How do I change how vectors look?

	You can have your model’s vectors displayed in several different ways:  with their x, y, and total components   in different colors (velocity, acceleration, and force vectors only) at their point of application or the center of mass (COM) of the body they act upon (force vectors only) You change how your vectors look with the Vector Display command in the Define menu.
1.	Open the Define menu and choose Vector Display.
2.	Click the Name, X, Y, or Magnitude checkboxes to put Xs in for the options you want. (If they are already checked, skip this step.)
3.	Press the Line Thickness palette, then select one of the thicknesses.
4.	Press each of the Color palettes (Velocity, Acceleration, and Force), then select the colors you want for each.
5.	Click the two boxes that show which way you want to have the force vectors drawn.
6.	Click OK.
	Now that you can change how the vectors look, you may want to add a few more to your model. Related Topics How do I display vectors? How do I turn off vectors? How do I adjust the length of a vector?


vector

A vector is an arrow whose length represents the magnitude of a quantity and whose direction represents the direction of a quantity.

A vector represents the properties of velocity, acceleration, and force as visual arrows. Vectors can be placed on points and bodies,

Vectors that designate velocity and acceleration point out from a body’s center of mass. Vectors that display force quantities can be either pointing from a body’s center or pointing in to a body’s center.

Vectors that display the collision forces that occur when bodies contact each other can be at the point of contact or at the mass center of each body.

Related Topics

How do I adjust the length of a vector?

How do I change how vectors look?

How do I display vectors?


About the World frame

In Working Model, simulations occur in ways consistent to basic external physical parameters called World parameters. When you create a new simulation document, the initial settings for the world are:

    Gravity:  Earth (9.81 m/s^2 )

    Air Resistance:  none

    Electrostatics:  none

    Force Field:  none

You can change these default values using the commands in the World menu.


How do I change gravitational values?

	When you create a new simulation document, the World parameters are set to default values. The default value for gravity is for Earth at 9.81m/s^2. If you want to work with a different value (perhaps a more exact gravitational constant or the Moon’s gravitational constant), use the World menu.
1.	Open the World menu and choose Gravity.
2.	Click which type of gravity you want to have in your simulation: None, Vertical, or Planetary. When None is selected, it indicates that gravity is not active. Vertical gravity creates a vertical field, like that near the surface of the Earth. Planetary produces a gravitational interaction between each pair of objects.
3.	Type a value to adjust gravity in your simulation. When adjusting vertical gravity, you are changing the value of g that relates the force of an object with its mass (F = mg). When adjusting planetary gravity, you are changing the value of "G", the universal gravitational constant.
4.	Click OK to close the Gravity dialog box.
	This may be the only time you can change gravity — unless you become an astronaut. Related Topics How do I change the air resistance? How do I activate electrostatic effects? How do I change the force fields?


How do I change the air resistance?

	Air resistance is a force on a moving body that is opposite to the direction of the body’s motion.   Working Model uses the cross section of the body to calculate air resistance. Thus, a 1-meter diameter circle has the same air drag as a square 1 meter on edge — even though this is not always realistic. You can change the air resistance values in the World menu.
1.	Open the World menu and choose Air Resistance.
2.	Click which type of air resistance you want to have in your simulation: None, Low speed, or High speed. When None is selected, it indicates no air resistance is taken into account in the simulation.  At low speed, air resistance uses a force proportional to an object’s velocity. At high speed, air resistance uses a force proportional to the square of an object’s velocity.
3.	Drag the slider or type a value to adjust the air resistance in your simulation. Using the default value gives good results in the standard workspace.
4.	Click OK to close the Air Resistance dialog box.
	Now you have air resistance values that simulate the environment that you want. Note: To model air resistance in 3-D, you have to modify the air resistance coefficient (k) as indicated below: To model a sphere, multiply k by pi*r/2 (where r is the radius of the sphere). To model a cylinder, multiply k by W (the width of the cylinder into the screen). To model a square, multiply k by W (the width of the rectangular box into the screen). Related Topics How do I change gravitational values? How do I activate electrostatic effects? How do I change the force fields?


How do I activate electrostatic effects?

	When you create a new simulation document, the World parameters are set to default values. The default value for Electrostatics is none — electrostatic effects are not considered in simulations.  If you want to have electrostatic effects in your simulations, you must activate this feature through the Electrostatics command in the World menu.
1.	Open the World menu and choose Electrostatics.
2.	Click On.
3.	Click OK.
	Now you have electrostatic effects in your simulation. Related Topics How do I change gravitational values? How do I change the air resistance? How do I change the force fields?


How do I change the force fields?

	You can add specific force fields that will act upon your model during simulation. For example, you can simulate wind forces by applying a horizontal force that varies randomly with time. You can define forces that act upon each object or each pair of objects with the Force Field command in the World menu.
1.	Open the World menu and choose Force Field.
2.	Open the Sample Force pop-up menu and choose a sample formula to use as a reference. If you use one of the supplied samples, the type of force and the formula for that force are filled in for you automatically. If you choose custom, you will have to make up your own formula. See Using Formulas and Formula Reference in the User’s Manual. After typing in a custom formula, click either Pair-Wise or Field to select the type of custom global force. If you select Pair-Wise, the new force will work between two bodies. If you select Field, the force will work on all objects in the same manner.
3.	Click OK.
	Now you can have special force fields applied to your model during simuation. Related Topics How do I change the air resistance? How do I activate electrostatic effects? How do I change gravitational values?


air resistance

Air resistance is the friction that acts on something moving through air.


reference frame

An object remains stationary on the screen — when it is selected as the reference frame object — while the other objects move around it. Working Model allows you to choose any object as the current reference frame. The default reference frame is the background, or World. To change from the World frame, use the New Reference Frame command in the View menu.

You can use reference frames to watch a simulation from any object’s point of view. You can attach reference frames to points, to the model’s center of mass, and to bodies.

	Also, you can use reference frames to jump quickly between various views of a simulation. A reference frame contains the current settings of Scroll and Zoom. Keyboard equivalents allow you to toggle quickly between different reference frames.  You can see the keyboard equivalents in the View menu.


tracking

Tracking leaves an image of a moving object — for bodies and constraints only—at adjustable time intervals. You can track individual objects or all objects.

Objects can leave visible tracks of their outline, center of mass, or vectors, so that you can follow the physical action throughout a simulation.

You control tracking through the Tracking command in the World menu and the Tracking options in the Appearance window.


World frame

In Working Model, the parameters you define using the commands in the World menu determine how your model will react in a simulation. Your model’s "world" can be anything from standard Earth conditions to the Moon... and beyond!

You can customize the World parameters to have your models react in unusual, but consistent, ways.

Related Topics

How do I activate electrostatic effects?

How do I change gravitational values?

How do I change the air resistance?

How do I change the force fields?


About meters

You can measure almost any physical property in a simulation. Meters allow you to get numerical and graphical information about your simulation.

You can use standard meters or customize meters to measure, display, or evaluate arithmetic and mathematical expressions.

Meters go into a different layer of your document so they don’t interfere with the actual simulation.


How do I add a meter?

	Meters allow you to get numerical and graphical data about your simulation. With them, you can measure almost any physical property in your simulations. You use the Measurement menu to add meters to your simulations.
1.	Select one body, point, or constraint object whose properties you wish to measure. (You can select two bodies to measure properties that apply to a pair of bodies.)
2.	Open the Measure menu and choose the property you want to measure. (Some properties have submenus.) To choose Contact Force or Friction Force, you must select two bodies before opening the Measure menu.
	Once you have a meter in your workspace, you can modify, move, or delete it — just like you do with other objects. Related Topics How do I modify a meter? How do I change a graph’s scale? Why can’t I drag a control or meter?


How do I modify a meter?

	Working Model allows you to modify meters in several different ways. You can change a meter’s display, change what it measures, and change its appearance.

To change a meter’s display:

1.	Select the meter you want to change.
2.	Press the arrow button on the top left corner and select the type of display from the pop-up menu.

To change what a meter measures:

1.	Select the meter you want to change.
2.	Open the Window menu and choose Properties. or Double-click the object.
3.	Replace the default formulas with your own formulas. For more information about formulas see "Using Formulas" and "Formula Language Reference" in the User’s Manual.

To change a meter’s appearance:

1.	Select the meter you want to change.
2.	Open the Window menu and choose Appearance.
3.	Enter a new name for the meter in the text box below the pop-up menu.
4.	Select each option you want by clicking its checkbox to put an X in it. (If they are already checked, skip this step.)
5.	Enter a new name for a variable in the text box on the left.
6.	Press the Color palette and select a new color to change a variable’s color (in a graph or bar chart only).
	Once you have a meter in your workspace, you can modify it to suit yourself. Related Topics How do I add a meter? How do I change a graph’s scale? Why can’t I drag a control or meter?


How do I change a graph's scale?
How do I change a graph’s scale?

	When you display meters as a graph, Working Model auto-scales data to fit within the display area of the graph.  If you want to display only part of the data on the graph, you can change the graph’s scale in the Properties window.
1.	Select the meter you want to change.
2.	Open the Window menu and choose Properties. or Double-click the object.
3.	Click the Auto checkbox to remove the X for the variable that you want to scale.
4.	Type Min and Max values for the variable you want to scale.
	Now, you can have your graphs show the data that is most important to you. Related Topics How do I add a meter? How do I modify a meter?


How do I export a meter's data?
How do I export a meter’s data?

	You can export the data from any meter as a tab-delimited text file. After exporting, you can edit this data with a word processor, spreadsheet, or graphics application. To do this, you use the Export command in the File menu. Also, you can capture meter data  by selecting a meter and then choosing Copy Data from the Edit menu. The data will be copied to the Clipboard. Then you can paste the data into any application that supports tab-delimited text.
1.	Open the File menu and choose Export.
2.	Open the Type pop-up menu and choose Meter Data.
3.	Click Export Options.
4.	Make any changes to the export options, then click OK.
5.	Click Save.
	Meter data is exported as a tab-delimited text file. The data is stored in columns, with each row representing a new simulation frame. You can open the exported file with any word processor or spreadsheet program.  Related Topics How do I import data for an input control? How do I modify a meter? How do I add a meter?


Why can't I drag a control or meter?
Why can’t I drag a control or meter?

If you cannot drag a control or meter, the Lock Controls feature in the View menu may be on. This feature prevents you from moving meters and controls inadvertently when you are editing your model.


control

A control allows you to adjust simulation parameters — before and while a simulation is running. A control can be a slider (default), a text box, or a button. Also, you can use a control to import data from a text file.

Related Topics

How do I create a control?

How do I import data for an input control?


layers

In Working Model, simulations have two layers: one for your model (built from bodies and constraints) and one for other objects (like meters and controls). When you run a simulation of your model, no object in the other layer (like a meter or control) will interfere with your model’s motion.


meter

Meters allow you to get numerical and graphical data about your simulation. You can measure almost any physical property in a simulation.

Besides the standard measurements that are available, you can customize meters to measure, display, or evaluate arithmetic and mathematical expressions.

Related Topics

How do I add a meter?

How do I modify a meter?

How do I export a meter’s data?


About simulations

Once you build your model, you run the simulation to see how your model acts. You can control your simulations in several ways:

use the commands in the World menu

use the buttons at the top of the toolbar

add buttons directly to the simulation document

use the tape player controls

use scripts

While your simulation is running, Working Model saves the values in a history file. If you re-run a simulation, it will run faster since the values do not need to be recomputed — unless, of course, you change your model.


How do I control a simulation?

	Once you create a model in the workspace, you can see the simulation in action. Working Model allows you to control your simulations in several ways.
	Ways to run a simulation: Click Run in the toolbar. Open the World menu and choose Run.      Shortcut: Ctrl-R If Run is not available in the toolbar or the World menu, the simulation is running.       If you click Run after stopping a simulation, the simulation continues from its current state. If you want to start the simulation over from the beginning, you must reset the simulation before running it.
	Ways to stop a simulation: Click Stop in the toolbar. Open the World menu and choose Stop.      Shortcut: Ctrl-R Click anywhere within the window if the cursor appears as a Stop sign. If Stop doesn’t appear in the toolbar or the World menu, your simulation isn’t running. You can stop the simulation and then run it again without resetting.
	Ways to reset a simulation: Click Reset in the toolbar. Open the World menu and choose Reset.        Shortcut: Ctrl-T If Reset doesn’t appear in the toolbar, you have already reset your simulation.
	Now that you know how to control your simulations, you may want to get even more control by using the tape player. Related Topics How do I use the tape player controls? How do I save a simulation?


How do I use the tape player controls?

	While you run a simulation, Working Model records it. The tape player allows you to play simulations backwards, to skip frames, and to play simulations more quickly after all calculations have been completed. The tape player controls indicate the number of frames in the simulation. The Tape Player Controls command in the Workspace submenu of the View menu shows and hides the tape player controls.
1.	Open the View menu and choose Workspace, then choose Tape Player Controls from the submenu. (Skip this step if the tape player controls already appear at the bottom of your workspace.) This is a toggle command to show and hide the tape player controls.
2.	Click the right arrow on the Player bar to run your simulation.
3.	Click the double bars on the Player bar to stop your simulation.
4.	Click the left arrow on the Player bar to run your simulation backwards.
5.	Click the right arrow with a bar on the Player bar to step through your simulation frame by frame. or Click the left arrow with a bar to step backwards.
6.	Drag the frame indicator left or right to move quickly to any frame. or Click any portion of the gray region to move the frame indicator to that location immediately. If you click the right arrow on the Player bar after moving the frame indicator, the simulation runs from that point. When the end of the recorded simulation is reached, Working Model will continue the simulation. To continue the simulation beyond the current recording, drag the frame indicator as far to the right as it will go and then click the right arrow on the Player bar. Working Model will continue the simulation.
	With the tape players controls you have a lot more flexibility in viewing your simulations. After carefully viewing and editing your simulations, you may want to save them permanently. Related Topics How do I save a simulation? How do I control a simulation?


How do I save a simulation?

	Once you get your model to run the way you want it to, you can save your simulation to run it again at another time. When you save a simulation file, Working Model automatically saves the tape history for the simulation. The saved simulation runs faster because the calculations don’t need to be done. You use the Save As command in the File menu to save your simulations the first time.
1.	Open the File menu and choose Save As.
2.	Locate the folder where you want to save your simulation.
3.	Type the name for your simulation and click Save.
	The model, initial conditions, and the simulation’s time history are saved to disk.  When you open this simulation, the tape player memory will be filled with the saved time history, and the simulation will run quickly the first time through. Related Topics How do I use the tape player controls? How do I control a simulation?


Play bar

The Play bar appears at the bottom of a document below the Coordinates bar. The Play bar contains the Tape Player controls. With it, you can start, stop, and reverse a simulation once it has run. Also, you can go through a simulation frame by frame — either forwards or backwards.

Related Topics

How do I use the tape player controls?


script

A script is a small program in a special scripting language that you can use to control your simulations.

To run a script, open the Script menu and choose Run.  Then, find the file containing the script and click OK.

For additional information, see "Running Scripts" in the User’s Manual.


simulation

A simulation is the running mode of an Working Model model. When you click Run, the bodies and constraints in the created model act in their defined ways — usually to produce motion.

Related Topics

How do I control a simulation?

How do I save a simulation?


simulation history

Working Model saves a simulation history in memory as it calculates each frame of a simulation. If no part of the model is changed, Working Model does not need to spend time computing the simulation again.

Therefore, if you want to demonstrate a simulation to an audience, you can run the simulation to a certain point, save the simulation, then re-open the simulation later, and play it back. The playback will be faster than the original simulation because no new calcuations are made.

Related Topics

How do I control a simulation?

How do I save a simulation?


About simulation enhancements

Once you create your model and get the basic simulation running the way you want, then it’s time to improve your simulation.

You can add pictures, link several simulations together, and add controls to change initial conditions. Additionally, you may want to add text to make your simulations easier for others to understand.


How do I create a control?

	Controls allow you to adjust simulation parameters — before and while a simulation is running.  To create a control for a body or constraint, you use the New Control command in the Define menu.
1.	Click a body or constraint to select it.
2.	Open the Define menu and choose New Control, then choose the type of control you want from the submenu.
	You can have more than one control for an object. For example, you may want to control both the initial x and y velocity of a ball.  You can position the control anywhere on the screen by dragging it or selecting it and typing values in the Coordinates bar. Related Topics Why can’t I drag a control or meter? How do I change a control’s properties? How do I change a control’s appearance?


How do I change a control's properties?
How do I change a control’s properties?

	When you create a control, it initially appears as a slider, which is the default. You can change a control into a text box or a button using the control’s Properties window.
1.	Click the control to select it.
2.	Open the Window menu and choose Properties. or Double-click the object.
3.	Click the type of control you want to have.
4.	Set the values for the control. If you selected a table, it reads its value from a table file, a tab-delimited ASCII text file with multiple columns. By default, Working Model assumes that the first column of data holds time and the second holds the corresponding control values. If you selected a button, select one of the two values specified in the min and max boxes. A button can act as a toggle switch or as a press-and-hold button. A text box allows you to enter an exact value for the property.
	Also, you can change how the control looks by using the Appearance window.  Related Topics How do I change a control’s appearance? How do I create a control? Why can’t I drag a control or meter? How do I import data for an input control?


How do I change a control's appearance?
How do I change a control’s appearance?

	You can change the appearance of a control by changing its color and name. You do this using the Appearance window.
1.	Click the control to select it.
2.	Open the Window menu and choose Appearance.
3.	Press the Color palette, then select a color for the control.
4.	Type a new name for the control in the text box, and press Tab or Enter.
5.	Click the Show Name checkbox to put an X in it.  (If it is already checked, skip this step.)
	Now you can have your controls color-coordinated with the rest of your model. Related Topics How do I create a control? How do I change a control’s properties? Why can’t I drag a control or meter?


How do I import data for an input control?

	You can use the output data of a meter as input to control other objects.  This information is exported as a tab-delimited text file. If you are using a word-processing program to edit it, make sure that the file is saved as a text (or an ASCII) file to be able to import it back in. You import data for an input control using the control’s Properties window. While the output data is recorded after each frame is computed, that data, when used input data, will specify the values at the beginning of each frame — before any computation.
1.	Click the control to select it.
2.	Open the Window menu and choose Properties. or Double-click the object.
3.	Click the Table icon.
4.	Click the Read Table button.
5.	Locate the text file that you want to import and double-click it.
6.	Specify which columns you would like to use as time and data references. Setting 0 as the time column indicates that Working Model will read data row by row for every animation frame. You must specify a positive number for the data column — you cannot specify 0 as the data column.
	The data values from the imported file are changed into a continuous linear function. Working Model reads this function to get a data value at each time step. Related Topics How do I export a meter’s data? How do I create a control? How do I change a control’s properties?


How do I add menu buttons?

	You can access common commands directly in the workspace with menu buttons. Clicking a menu button is exactly the same as choosing the command from a menu. You add menu buttons with the New Menu Button command in the Define menu.
1.	Open the Define menu and choose New Menu Button.
2.	Open the appropriate menu and choose the command that you want the button to perform. The command’s name appears in the dialog box and the OK button becomes active.
3.	Click OK.
	Once the menu button appears, you can control your simulations easily — right from the workspace. Related Topics How do I create a control? How do I work with text?


How do I work with text?

	You can add text to your models to label your simulations and add other information. Labels are considered text objects. Once you have a text object, you can edit, change its appearance, or delete it. You use the Text tool in the toolbar to add text to your model.
1.	Click the Text tool in the toolbar.
2.	Click where you want to add text and begin typing.
3.	Select all or part of the text. You can use the Arrow tool to select the text object or use the Text tool to select all or part of the text in the text object.
4.	Type new or additional text to edit a text object.
5.	Select all or part of the text. You can use the Arrow tool to select the text object or use the Text tool to select all or part of the text in the text object.
6.	Open the Object menu, choose Font (or Size or Style), then choose the font (size or style) you want from the submenu. The new change affects all the text in that text object.
7.	Click the Arrow tool, select a text object, and press Delete to delete a text object.
	In addition to text that you add with the Text tool, you can have object names appear on the screen. You do this with the object’s Appearance window. Related Topics How do I change a body’s appearance? How do I change a control’s appearance? How do I modify a meter?


How do I add pictures?

	If you create a picture in a graphics program, you can copy it to the Clipboard and paste it into your model. It then becomes a Working Model picture object. You can drag, cut, copy, and paste picture objects.  You can attach picture objects to bodies. To do this, you use the Attach Picture command in the Object menu.
1.	Copy a picture from your graphics application to the Clipboard.
2.	Open the Edit menu and choose Paste. (The Paste command becomes active when you have something in the Clipboard.)
3.	Press the Shift key and click the picture and a body.
4.	Open the Object menu and choose Attach Picture. A picture does not zoom or rotate with the attached body. It is best to attach a picture to a body that has linear, rather than rotational, motion.
	The picture moves on top of the object. If you change your mind, select the body with the attached picture and use the Detach Picture command in the Object menu. Related Topics How do I work with text? How do I create a body?


How do I link multiple documents?

	With menu buttons, you can link simulations together to build sequential activities. To do this, you use the New Menu Button command in the Define menu.
1.	Create the simulation documents you want to link, and, for convenience, store them in the same folder.
2.	Open the File menu and choose Open.
3.	Locate the simulation that you want to start with and double-click it.
4.	Open the Define menu and choose New Menu Button.
5.	Open the File menu and choose Open. Locate and select the next file, and click Open. The Open command appears in the dialog box and the OK button becomes active.
6.	Click OK.
	Continue this procedure for all the documents you want to link together.  When you click the Open button in one document, that document closes and the next one opens automatically. Related Topics How do I add menu buttons? How do I create a control?


Coordinates bar

The Coordinates bar appears at the bottom of an open document. It displays the coordinates (either Cartesian and, possibly, polar) for the selected object. If a tool is selected, the coordinates of the tip of the tool appear here as you move it around the workspace.


How do I avoid inconsistent initial velocities?

	Working Model maintains consistency for the positions of objects, but not for their velocities. Objects can have inconsistent velocities if they are unable to move initially in the correct direction.  For example, a body that is pinned to the background will have an inconsistent velocity if its initial velocity is directed at the pin joint rather than perpendicular to the pin joint. Large correcting forces will be applied to objects that have inconsistent velocities in the initial frames of a simulation.


How do I best use automatic features?

	Always start in Accurate mode in the Simulation Accuracy dialog box when building a new model. Accurate mode is the default setting for a new document, and it sets the internal step size as variable. This enables the automatic time step control in Working Model, and gives accurate and stable results. Accuracy is set in the Simulation Accuracy dialog box (the Accurate command in the World menu). Any warning messages that appear at the beginning of a simulation should not ignored. You should identify the source of the problem and correct it.
	A common error message concerns overlapping bodies. If you see the message, first identify which bodies are overlapping and colliding. Then, turn off collisions between them or adjust the parts for proper clearance.  If you have trouble identifying undesired collisions, first select all objects (using Select All in the Edit menu). Then, turn on contact force vectors (using the Vectors submenu in the Define menu) and watch for unexpected force vectors as the simulation runs.


How do I build and debug a complex model?

	Instead of trying to model all the components of a complex model right away, start with a simplified model (20 objects or less) and get that model working first.  Although this initial model may not be accurate enough for meaningful analysis, it serves a few purposes: It allows you to lay out the major components and verify their behavior.  A simple system is easier to debug if its behavior is unexpected.  You can take order-of-magnitude measurements early in the model development. This will help you identify any system-level issues.
	Once you model the basic system, increase the model gradually — verifying overall behavior at each step. This approach might seem slower than the everything-at-once approach, but it is actually much faster since it saves a lot of debugging time. Another useful approach is to model subcomponents in separate Working Model documents. You can test them as standalone subcomponents, then incorporate them in the main model by copying and pasting.


How do I build complex objects?

	You can use rigid joints to build large, complex objects from simple shapes. It is easier to create a hollow box shape by rigidly joining four rectangles than it is by sketching a complex polygon.  Rigid joints do not add extra equations of motion in a simulation, and, therefore, using rigid joints is preferable to using two pin joints when locking objects together.


How do I control a simulation's duration?
How do I control a simulation’s duration?

	The Pause Control dialog box can be used to stop a simulation automatically at any time. You access this using the Pause Control command in the World menu.  In the dialog box, type an equation using the word "time" in one of the pause condition fields, and then use the pop-up menu to specify what should happen (Stop, Pause, Loop, Reset) when the condition is met.  Sample conditions include "time > 1.0", or "frame() = 30". When using an equal "=" sign in a pause condition, make sure that the condition will really occur. If the time step is set to 0.97 seconds, the time will never exactly equal 1.0 second.


How do I control WM from another application?

	Working Model can exchange data in real time with other applications using DDE. In this case, Working Model serves as a client using the capabilities in other application, which acts as a server. Working Model sends data to and receives data from the other application once every animation time step.
	Working Model can communicate with applications that support DDE (Excel Table or Text formats). These applications include Microsoft® Excel, Quattro Pro, MATLAB (version 4.2 or later), and Microsoft Word for Windows. Check with your particular application’s user guide to see if DDE is supported. To activate this feature, use the New Application Interface command in the Define menu. See "Exporting Files and Data" in the User’s Manual for more detail.


How do I determine the best time step?

	The size of a time step is critical in fixed step numerical integrators because it significantly affects the speed and accuracy of the results. In general, a small time step produces more accurate simulation results, but requires more computation than a larger time step. Basically:      Small time step = improved accuracy      Large time step = improved speed You do not have to have a very small time step just because you are concerned about accuracy. More often than not, a reasonably small step size produces a simulation result with sufficient accuracy.
	If you use the variable time step feature, Working Model automatically chooses the appropriate time steps and monitors simulation errors of various types for you. But if you want to set your own time step, you might begin simulating a problem with a large time step so you can obtain a rough idea about the model. When you want precise details, you can use a smaller time step and let Working Model run a long simulation to verify the model’s accuracy.


How do I make a simulation run faster?

	A small change in the model may require a lot less computer power and may speed up your simulation while maintaining accuracy. Here are some modifications to consider for faster simulations. Select Fast in the Simulation Accuracy dialog box (use the Accuracy command in the World menu), and set the time step to the largest value that allows a stable simulation and acceptable accuracy. Reduce the number of objects that are in contact. Make sure to use the Do Not Collide command with all objects that do not need to collide.  Use rigid joints to build complex objects.  Use rods instead of ropes wherever possible. Use rods instead of pinned bodies wherever possible. Make your window size smaller. Reduce the number of colors in the model.  Set the frictional coefficients of contacting objects to 0.0 if friction is not needed in your simulation.
	For faster animation when you playback a simulation, you can skip frames. Open the World menu and choose Skip Frames, then select the number of frames to skip from the submenu. Skipping frames does not affect the accuracy of your model, because the simulation has already been run and all frames have been stored in the tape player.  It only affects how many frames are played back when you use the tape player controls.


How do I minimize collisions?

	You can control whether any two objects are meant to collide. By default, Working Model makes all objects collide, except those that are directly connected to each other with a joint or gears. You have complete control about whether multiple objects do or don’t collide with each other.  If your simulation has many objects that overlap, Working Model will compute collision forces for each pair of overlapping objects. The computation is not wasteful, but can cause slow and unstable simulations.
	Make sure that only the objects that you want to collide are actually designated to collide. For a model with many objects (more than 20),  start out by selecting all objects in the workspace (use Select All in the Edit menu) and choosing Do Not Collide from the Object menu. You can then select sets of bodies that ARE meant to collide and apply the Collide command to them.


How do I prevent objects from penetrating?

	Working Model allows objects to penetrate each other a little. When two fast-moving objects collide, you may find them overlapping each other by an unacceptably large distance. This penetration distance can be controlled using the Accuracy command in the World menu.  Using the Accurate simulation mode will deal with most interpenetration problems. In variable time step mode, the results of two small time steps are compared to the result of a single time step. If the difference in object positions is large, a smaller time step will be used.  Smaller time steps almost always improve simulation results. You can use either a smaller animation step or a smaller integration time step.


How do I prevent rebounding inelastic collisions?

	When objects with zero elasticity collide and they overlap by a large distance, a small correctional force is applied to bring the overlap distance back to the amount specified in the Overlap Error field of the Simulation Accuracy dialog box. This force will tend to push the objects apart. You can make sure that objects with 0 elasticity do not rebound by setting the Accurate simulation mode using the Accurate command in the World menu. Also, smaller time steps almost always improve simulation results. You can set either a smaller animation step or a smaller integration time step in the Simulation Accuracy dialog box to prevent rebounding.


How do I prevent simulations from slowing down?

	When your model reaches a "difficult" configuration — one with many colliding objects or large accelerations — Working Model decides to use smaller integration time steps to maintain accuracy. This results in more computations for each animation frame. Consequently, the simulation will appear as if it were slowing down. To minimize this, keep the number of colliding objects as small as possible. Also, you could lock the integration time step to keep it constant.  See "Integration Time Step" in the "Technical Information" chapter of the User’s Manual.


How do I put a body directly on another?

	A Working Model simulation can be used to align bodies. Take, for example, a block that needs to rest exactly on an inclined plane. Select both the block and the plane, and set their frictional coefficients to a high value like 1.0. Place the block so it is approximately in position over the plane, and then run the simulation. The block will come to rest in a stable position.  Stop the simulation at this time, and choose Start Here from the World menu. This will make the stable, settled position the initial condition. The block will be perfectly aligned on the plane.


How do I put a point on the edge of an object?

	To place a point directly on the edge of a body, first put the point inside the body — near to, but not on, its edge. Then select the point and choose Properties from the Window menu. In the Properties window, enter an offset that will place the point directly on the object’s edge.


How do I run a long simulation?

	Recording a simulation can take up a great deal of memory. The amount depends on how many objects, meters, and vectors the model has. Working Model automatically uses all available memory to store large simulations. There are ways you can make more space available to run a longer simulation.
	Ways to increase memory for simulations: Close other Working Model documents to make more memory available to the tape player. Let the tape player "loop" and continue running the simulation. Increase the time step of the simulation. This gives more space between frames and allows you to record the simulation for a longer time.
	Now you can record long simulations that you might want to save. Related Topics How do I save a simulation? How do I control a simulation?


How do I run a simulation unattended?

	When you create a complex model, you may need to run Working Model for a long time to obtain simulation results. For example, you may let a simulation run overnight. If you decide to run a simulation unattended, make sure that Working Model can continue its computations uninterrupted.  The warning dialog boxes should be disabled so that the simulation will continue without interruption. There should be enough memory available for Interactive Phyics to run the simulation and store its results.
1.	Open the World menu and choose Accuracy.
2.	Click the More Choices button.
3.	Click the checkboxes in the Warnings area to remove the Xs. (If a checkbox is already unchecked, skip it.)
4.	Click OK to close the Simulation Accuracy dialog box.

Ways to increase memory for simulations:

Close other Working Model documents to make more memory available to the tape player.

Increase the time step of the simulation. This gives more space between frames and allows you to record the simulation for a longer time.

Close all other applications to maximize the amount of memory available for Working Model.

To select (or de-select) looping, use the Preferences command in the World menu.

Options for long simulations:

Let the tape player "loop" and continue running the simulation. This option is useful when, for example, you want to observe the steady state of a dynamic system after a long transient state, which may take a long time to compute.

Stop the tape player from looping. If you prevent looping, Working Model will pause the simulation automatically when memory runs out, preserving the simulation history obtained thus far. If necessary, you can continue the simulation, discarding the history.

	Now, you can let the computer and Working Model work all night as you sleep. Related Topics How do I control a simulation? How do I run a long simulation?


How do I select connected objects?

	The pop-up menu at the top of the different utility windows (Properties, Appearance, Geometry) is a useful way to select objects in your model. You will notice that some of the entries (Points, Bodies, Constraints) appear in bold type. These entries are related in some way to the current selection. If you select a body object, all of the points that are connected to the body will appear in bold type in the pop-up menu. If you select a point, the body object to which the point is connected will appear in bold type. If you select a constraint, the points associated with the constraint will appear in bold type.


How do I use formulas?

	Working Model allows you to enter formulas in most places where you would type a number. With formulas you can customize: input controls meters bodies global forces frames of reference Formulas enable you to build custom forces and constraints and to control the behavior of objects dynamically. Formulas control the data displayed by meters and output devices. Formulas also serve as the underlying mechanism that links input controls to the simulation.
	You can use formulas in place of numbers in any field of a Properties window. This means that you can attach equations to govern the motion as well as the physical properties of bodies during a simulation. For example, you can use formulas to model the mass of a rocket that becomes lighter as its fuel is consumed. The force field feature of Working Model allows you to model many types of force fields that affect individual objects as well as pairs of objects. Formulas in the Force Field dialog box act as forces and torques on all objects.
	You can have your simulation run in a non-standard frame of reference. For example, you might want to track a moving object that would otherwise leave the screen at some point. You do this by defining a point with a formula, then attaching the frame of reference to the point.  See "Using Formulas" and "Formula Reference" in the User’s Manual for more detail.


elastic

Elastic is a term applied to material that returns to its original shape after it has been stretched or compressed.


electric charge

Electric charge is the property to which the mutual repulsion of electrons or protons, and the mutual attraction of electrons and protons is attributed.


electrostatics

Electrostatics is the study of electric charges at rest.


force field

Force field is what fills the space around a mass, electric charge, or magnet, so that another mass, electric charge, or magnet introduced to this region will experience a force.  Working Model lets you define gravitational, electrostatic, and magnetic force fields.


inelastic

Inelastic is a term applied to material that does not return to its original shape after it has been stretched or compressed.


inertia

Inertia is the resistance of a body to change its state of motion.


kinetic energy

Kinetic energy is the energy of motion equal to half the mass multiplied by the square of speed.


menu button

Working Model allows you to add buttons, which perform menu commands, to your simulations.

To put menu buttons in your simulations, use the New Menu Button command in the Define menu.

Related Topics

How do I add menu buttons?


potential energy

Potential energy is energy stored and held in readiness by an object by virtue of its position.


projectile

Projectile is an object projected by some force that continues in motion by its own inertia.


Rotate tool

	You use the rotate tool to rotate objects in your model.


Text tool

	You use the text tool to add text labels to your model.


hot text example

This is just to show you what it looks like. If this were a related topic, you would be in a whole new series of windows.

Click the close box to get rid of me.


underlined words

This is just to show you what it looks like. If this were a definition, you would have a new window appear like this with a definition on it.

Click the close box to get rid of me.


Step 1: Create the ball and table

	In this first step, you will create a ball and table to set up your basic model. Then you will run the simulation.
1.	If you have an existing model open, close it now.  Then, open the File menu and choose New. or If you have an empty document open, you are ready to get started.
2.	Click the Circle tool in the toolbar.
3.	Draw a small circle in the top of the workspace near the middle. The circle is a "circular mass object," but we’ll call it a ball.
4.	Click the Rectangle tool in the toolbar.
5.	Draw a long, horizontal rectangle along the bottom of the workspace underneath the ball. The rectangle is a "rectangular mass object," but we’ll call it a table.
6.	Click the Anchor tool in the toolbar.
7.	Click the table with the Anchor cursor. The table is anchored to the background, so it won’t move in the simulation.
8.	Click Run. The ball falls, bounces, and comes to rest on the table.
9.	Click Stop; then, Reset. The simulation stops and the model returns to its original location.

To save your model:

1.	Open the File menu and choose Save As.
2.	Locate the folder where you want to save your simulation.
3.	Type the name for your simulation and click Save.
4.	Click Save.
	Congratulations! You have set up your basic model and run your first simulation.  Look at the sample picture and make any adjustments to your model before proceeding. Next, you can change the appearance of the model: the ball, table, and the workspace. Steps 1. Create the ball and table. 2. Change the model’s appearance. 3. Change the ball’s properties.


Step 2: Change the model's appearance
Step 2: Change the model’s appearance

	In this step, you will use the Appearance window and other methods to change the way your model looks. You should have an open document with a ball and table.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Open the Window menu and choose Appearance.
3.	Click the ball to select it.
4.	Press the Color Fill palette and select the dark blue color.
5.	Click the table to select it.
6.	Press the Color Fill palette and select the brown color. Then, press the Pattern Fill palette and select the brick-like pattern.
7.	Open the View menu and choose Workspace, then choose Grid Lines from the submenu. With the grid lines in, you’ll be able to see how high the ball bounces.
8.	With the grid lines to guide you, drag the ball and table at least 3 grids apart. Be sure to keep the table under the ball. You may want to align the bottom of the ball and the top of the table to grid lines.
	You have "dressed up" your basic model. Compare your model to the sample here. Next, you can change the properties of the ball to see how it bounces. Steps 1. Create the ball and table. 2. Change the model’s appearance. 3. Change the ball’s properties.


Step 3: Change the ball's properties
Step 3: Change the ball’s properties

	In this final step, you will use the Properties window to change the material of the ball. This will affect the way the ball bounces on the table. You should have an open document with grid lines, a ball, and a table.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Click Run and notice how high the ball bounces.  Remember to click Stop; then Reset.
3.	Click Stop; then, Reset.
4.	Click the ball to select it.
5.	Open the Window menu and choose Properties. or Double-click the object.
6.	Open the material pop-up menu and select Clay. When you create a body, its default material is Standard, which actually has the density (and other properties) of water.  When you change the material, the other values (below the material pop-up menu) in the Properties window change. Related to this project, changing the material will change the ball’s elasticity.
7.	Click Run and notice how high the ball bounces.  Remember to click Stop; then Reset.
8.	Click Stop; then, Reset.
9.	Click the ball to select it.
10.	Open the material pop-up menu and select Rock. What do you think will happen?
11.	Click Run and notice how high the ball bounces.  Remember to click Stop; then Reset.
	Congratulations! You have bounced different types of balls on a table successfully.  Did you notice any difference in how high the ball bounced? If so, which ball bounced the highest? Which ball bounced the least?  Are you ready to try some other ideas with the bouncing ball? Suggested Explorations What happens if you change the ball’s  initial vertical velocity? What happens if you give the ball a spin (a rotational velocity)? How do I change body properties? What happens if you place another ball under the first and let them fall together? How do I create a body?


Step 1: Create a pendulum

	In this first step, you will create a ball for the pendulum and a rectangle for the ceiling. You will then attach a rope between them and set the pendulum in motion.
1.	If you have an existing model open, close it now.  Then, open the File menu and choose New. or If you have an empty document open, you are ready to get started.
2.	Open the View menu and choose Workspace, then choose Grid Lines from the submenu. The grid lines will help you align the objects.
3.	Click the Circle tool in the toolbar.
4.	Draw a small circle just below the center of your workspace.  Use the grid to align the center of the ball on a vertical line. This circle will be the ball in your pendulum.
5.	Click the Rectangle tool in the toolbar.
6.	Draw a thin rectangle across the top of your workspace at least two grid lines above the ball.  We will call this rectangle a ceiling.
7.	Click the Anchor tool in the toolbar.
8.	Click the Anchor tool once on the ceiling. The ceiling is anchored to the background, so it won’t move in the simulation.
9.	Click the Rope tool in the toolbar.
10.	Click once in the center of the ball and, using the vertical grid line to guide you, click the bottom of the ceiling directly above the ball. You now have a pendulum attached to the ceiling.
11.	Click the Pointer tool in the toolbar.
12.	Drag the ball to the left, so its center is on a horizontal grid line. Keep the rope taut as you drag the ball.
13.	Click Run to see what happens.  Click Stop, and then click Reset when you are ready to move on.
14.	Click Stop; then, Reset.

To save your model:

1.	Open the File menu and choose Save As.
2.	Locate the folder where you want to save your simulation.
3.	Type the name for your simulation and click Save.
4.	Click Save.
	Congratulations!  You have constructed your pendulum with a rope constraint.  Look at the sample here and make any adjustments to your model before proceeding.  Next, you will enhance your simulation by modifying your workspace. Steps 1. Create a pendulum. 2. Set tracking. 3. Add a time meter.


Step 2: Set tracking

	In this  step, you will enhance your simulation by adding a feature called tracking. This allows you to take "snapshots" of your pendulum as it moves.  You should have an open document with a pendulum.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Click the Pointer tool in the toolbar.
3.	Select the ball on the pendulum.
4.	Open the Window menu and choose Appearance.
5.	Click the Track center of mass checkbox to put an X in it, and click the Track outline checkbox to remove the X.  (Skip this step if the checkboxes are set this way already.)
6.	Open the World menu and choose Tracking, then choose Every 4 frames from the submenu.
7.	Click Run to check out your model.  Tracking allows you to see the instantaneous position of an object as it moves in time. The is very useful when you need to determine information about an objects motion during certain time intervals.
8.	Click Stop; then, Reset. The simulation stops and ball returns to its original location. Remember to erase tracking after you reset the simulation.
9.	Open the World menu and choose Erase Track. Shortcut: Ctrl-E You will want to keep your simulation from getting cluttered.
10.	Click Run, then Stop when the pendulum reaches its peak on the right side. Notice the spacing of the track. You set it for every 4 frames. Why is the spacing uneven?
	Congratulations!  You have learned how to track your pendulum’s movement. Feel free to experiment with other tracking values. You will now enhance your simulation by adding a time meter. Reset and erase the tracking before you move on. And, you may want to save your model, too — just in case.  Steps 1. Create a pendulum. 2. Set tracking. 3. Add a time meter.


Step 3: Add a time meter

	In this final step, you will add a time meter to your project. This will allow you to measure the exact period for your pendulum. The period is the time it takes for the pendulum to make a complete swing. You should have an open document with your pendulum in it.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Open the Measure menu and choose Time. A time meter appears on your workspace.
3.	Drag the meter so that it is out of the way of your pendulum.
4.	Click Run and notice the time meter.  As your simulation proceeds, the elapsed time appears in the meter. You can use the meter get time readings at specific positions.
5.	Click Stop; then, Reset. The simulation stops and ball returns to its original location. Remember to erase tracking after you reset the simulation.
6.	Click Run again. Then click Stop when the pendulum reaches its peak on the right side. Notice the time it takes to get from one side to the other. Remember to reset and erase the tracking before moving on. You may have to try several times to get it close.  Remember to Reset and use Ctrl-E to erase the track before trying again.
7.	Double-click the rope and type a new, shorter length in its Properties window. Don’t make it too short — maybe just .5 meter shorter.
8.	Drag the ball to get the center of the ball on a horizontal grid line, if possible.
9.	Click Run again. Then click Stop when the pendulum reaches its peak on the right side. Notice the time it takes to get from one side to the other. Remember to reset and erase the tracking before moving on. You may have to try several times to get it close.  Remember to Reset and use Ctrl-E to erase the track before trying again.
Try This	Did you notice any difference in how the length of the pendulum changed the time for a complete swing?  Try the following to apply what you have learned: Try other rope lengths.   Pull the ball back a different amount. Does the time period change?  Track the pendulum outline instead of the center of mass. Do you find this easier to work with? Feel free to experiment with what you have learned!
	Congratulations! You created a pendulum and modified its behavior. You also enhanced your simulation by adding tracking and a time meter. Suggested Explorations Change Gravity and measure the time for one swing. Did it get longer or shorter?  How do I change gravitational values?  Change the mass of the pendulum. Does this make a difference in the period? How do I change body properties? Change the constraint from a rope to a spring. What does this do to the simulation? How do I delete a constraint? How do I create a constraint?


Step 1: Create a projectile and define the workspace

	In this first step, you will  set up your basic model with a projectile, a floor, and a shelf.
1.	If you have an existing model open, close it now.  Then, open the File menu and choose New. or If you have an empty document open, you are ready to get started.
2.	Double-click the Rectangle tool in the toolbar.  The Rectangle tool will remain selected while you draw as many rectangles as you need.
3.	Draw a long, horizontal rectangle along the bottom of the workspace. The rectangle is a "rectangular mass object," but we’ll call it a floor.
4.	Click the Rectangle tool in the toolbar.
5.	Draw a short horizontal rectangle in the upper right corner of the workspace. The rectangle is a "rectangular mass," but we’ll call it a shelf.
6.	Double-click the Anchor tool in the toolbar. The Anchor tool will remain selected until you choose another tool.
7.	Click the shelf, then the floor. The shelf and floor are anchored to the background. This means they won’t move during the simulation.
8.	Open the Window menu and choose Appearance.
9.	Click the Arrow tool in the toolbar, then select each anchor, and click the Show checkbox to remove the X. (Skip this step if the Show checkbox for each anchor is clear.)
10.	Click the Circle tool in the toolbar.
11.	Draw a small circle and position it on the floor. The circle is a "circular mass," but we’ll call it a ball.

To save your model:

1.	Open the File menu and choose Save As.
2.	Locate the folder where you want to save your simulation.
3.	Type the name for your simulation and click Save.
4.	Click Save.
	Congratulations!  You have set up your projectile system with a ball on the floor and a shelf as a target.  Look at the sample picture and make any adjustments to your model before proceeding.  In the next step, you will add controls to your ball so you can get it to land on the shelf. Steps 1. Create a projectile and define the workspace. 2. Create and edit input controls. 3. Change the model’s world.


Step 2: Create and edit input controls

	In this step, you will add Vertical (Vy) and Horizontal (Vx) velocity controls to your ball so that you can control its initial conditions. You should have an open document with your projectile model.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Click the ball to select it.
3.	Open the Define menu and choose New Control, then choose Initial X Velocity from the submenu.
4.	Open the Define menu and choose New Control, then choose Initial Y Velocity from the  submenu.
5.	Drag and position the controls if necessary. You will want them out of the projectile’s possible path.
6.	Adjust the Vx and Vy input controls and run your simulation until your ball lands on the the shelf. This may take some practice. Feel free to experiment with different combinations. Remember to Stop and Reset each time. The input controls can be adjusted by dragging their sliders up and down.  You can get a specific value by typing a number in the box under the slider.
	Congratulations!  You have learned how to use input controls to change the velocity of your projectile. In the next step, you will change World parameters and enhance your workspace. Steps 1. Create a projectile and define the workspace. 2. Create and edit input controls. 3. Change the model’s world.


Step 3: Change the model's world
Step 3: Change the model’s world

	In this final step, you will change World parameters for your model. In addition, you will add text to make your model more descriptive. You should have an open document with the projectile model.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Open the World menu and choose Gravity.
3.	Enter 1.670, the gravitational constant for the moon.
4.	Click OK to close the Gravity dialog box.
5.	Click Run.  Notice how the velocities you applied in Step 2 affect the ball‘s motion differently because of the different gravity condition.
6.	Click Stop; then, Reset. The simulation stops and the model returns to its original location.
7.	Open the World menu and choose Air Resistance.
8.	Click High.
9.	Click OK to close the Air Resistance dialog box.
10.	Click Run.  Notice what effect your initial velocities (that worked before) have on the projectile now.
11.	Click Stop; then, Reset. The simulation stops and ball returns to its original location. Remember to erase tracking after you reset the simulation.
12.	Click the Text tool.
13.	Type a short description of your project in the workspace.  This is a great way to have a complete description of a problem and its simulation together in one place!
Try This	Apply what you have learned to try the following: Change the air resistance back to none and see if you can get your projectile to land on the shelf. What happened? Change the gravity setting back to Earth. What happens now? Use other air resistance settings with Earth gravity. Feel free to experiment with what you have learned!
	Congratulations! You have successfully landed your ball on a shelf with different world conditions. Did you notice any difference in how high the ball went each time? Imagine all the parameters that must be considered for launching the space shuttle through the Earth’s atmosphere. Suggested Explorations Change the mass of the ball and watch what happens. How do I change body properties? Add a force to the ball and watch what happens. How do I apply a force or torque? Try dropping the ball on floor and getting it to bounce onto the shelf.


Step 1: Create billiard balls and set the background

	In this first step, you will create two billiard balls and set up your model’s world.
1.	If you have an existing model open, close it now.  Then, open the File menu and choose New. or If you have an empty document open, you are ready to get started.
2.	Open the View menu and choose Workspace, then choose Grid Lines from the submenu. The grid lines will help you align the objects.
3.	Double-click the Circle tool in the toolbar.  The Circle tool will remain selected to draw multiple circles, until you select another tool.
4.	Draw two circles about 1 vertical grid line apart, but on the same horizontal grid line.  We will call these two circles billiard balls.
5.	Select the Arrow tool and double-click the first ball.
6.	Open the Window menu and choose Properties. or Double-click the object.
7.	Type the first ball’s Vx as 5 m/s,  mass as 10 kg, and its elasticity as 1.0 in the Properties window.
8.	Select the second ball. Set its Vx to 0 m/s, the mass to 10 kg and elasticity to 1.0 in the Properties window.
9.	Open the World menu and choose Gravity.
10.	Click None; then click OK. This will simulate a horizontal surface, so the billiard balls behave like they are on a pool table.
11.	Click Run to see what happens.  Click Stop, and then click Reset when you are ready to move on.
12.	Click Stop; then, Reset. The simulation stops and the balls return to their original locations.

To save your model:

1.	Open the File menu and choose Save As.
2.	Locate the folder where you want to save your simulation.
3.	Type the name for your simulation and click Save.
4.	Click Save.
	Congratulations! You have set up the basic model and had your first collision. And, you didn’t have to worry about insurance! Look at the sample picture and make any adjustments to your model before proceeding.  Next, you will analyze the motion of the two billiard balls. Steps 1. Create the billiard balls and set the background. 2. Add velocity vectors to the model. 3. Add momentum meters to the model.


Step 2: Add velocity vectors to the model

	In this  step, you will analyze the behavior of your billard balls as they interact with each other. You’ll do this by displaying vectors. You should have an open document with two billiard balls.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Select one ball.
3.	Open the Define menu and choose Vectors, then choose Velocity from the submenu. Go through the same procedure for the other ball.
4.	Click Run and notice how vectors relate to the motion of the two the billiard balls. Why do you think they are acting this way during the simulation?
5.	Click Stop; then, Reset. The simulation stops and the balls return to their original locations.
	Good! You have added vectors to your model. Vectors are very powerful visualizing tools for any scientist.   Be sure to save your project before moving on to the next step. Steps 1. Create the billiard balls and set the background. 2. Add velocity vectors to the model. 3. Add momentum meters to the model.


Step 3: Add momentum meters to the model

	In this final step, you will attach a meter to each billiard ball. This will allow you to measure the momentum of the balls as they interact.  You should have an open document with two billiard balls.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Select one ball.
3.	Open the Measure menu and choose Momentum.  Do the same for the other ball.
4.	Drag each meter so that it is below the ball it is measuring.
5.	Click Run and notice how the meters and vectors change in this collision. What do you learn from this? Did you notice how the momentum is transferred from one ball to the other?
6.	Click Stop; then, Reset. The simulation stops and the balls return to their original locations.
7.	Double-click the second ball and change its horizontal velocity (Vx) to –1 m/s. Leave the other ball as is.
8.	Click Run and notice how the meters and vectors change in this collision. What do you learn from this? Did you notice how the momentum is transferred from one ball to the other?
9.	Click Stop; then, Reset. The simulation stops and the balls return to their original locations.
Try This	Apply what you have learned to try the following:  Move the first ball up slightly so that when it collides with the other ball, they both move at angles.  Change the vertical velocities. How do the vectors behave? Feel free to experiment with what you have learned!
	Congratulations! You have created a controlled collision and learned how to attach useful measuring tools. Using vectors and meters will display exact measurements in your simulations.  Suggested Explorations What happens if you change the material in one ball? Or both? How do I change body properties? Add a third ball and measure its behavior when all three collide.


Step 1: Create the box and incline

	In this first step, you will create a table with a box on it and rotate them to make an incline.
1.	If you have an existing model open, close it now.  Then, open the File menu and choose New. or If you have an empty document open, you are ready to get started.
2.	Double-click the Rectangle tool in the toolbar.  The Rectangle tool will remain selected while you draw as many rectangles as you need.
3.	Draw a long, horizontal rectangle in the middle of the workspace. The rectangle is a "rectangular mass object," but we’ll call it a table.
4.	Draw a box and position it so that it is just touching the table.  Don’t make the box too tall. Positioning it on the table may take a little patience.
5.	Click the Anchor tool in the toolbar.
6.	Click the table with the Anchor cursor. The table is anchored to the background, so it won’t move in the simulation.
7.	Click the table to select it.
8.	While holding down the Shift key,  click the box to select it.
9.	Click the Rotate tool in the toolbar.
10.	Rotate the selection clockwise about 30 degrees so that the table and box are inclined.  If both objects do not rotate together, make sure you have selcted both of them before you select the Rotate tool.   Notice that the angle is displayed on the right in the Coordinates bar.
11.	Click Run to test your model.  Remember to click Stop and Reset.  If you get an overlap warning, just click Continue for now. You can always fine tune your objects later.
12.	Click Stop; then, Reset.

To save your model:

1.	Open the File menu and choose Save As.
2.	Locate the folder where you want to save your simulation.
3.	Type the name for your simulation and click Save.
4.	Click Save.
	Congratulations! You have made your objects and rotated them together. Look at the sample picture and make any adjustments to your model before proceeding. Next you will add vectors to your project. Then, you can see the contact forces as the box slides down the incline. Steps 1. Create the box and incline. 2. Add vectors and edit mixed properties. 3. Measure the contact forces. 4. Apply external forces.


Step 2: Add vectors and edit mixed properties

	In this step, you will display vectors for the forces acting on the box. Also, you will change the frictional properties of the box and incline. The displayed vectors will reflect this change. You should have an open document with the box and the incline.  When an object is sliding down an incline, the forces acting on it are complex. By displaying vectors, you can view the different force to help you understand the physics behind the simulation.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Click the box to select it.
3.	Open the Define menu and choose Vectors, then choose Gravitational Force from the submenu.
4.	Open the Define menu again and choose Vectors, then choose Total Force from the submenu.
5.	Open the Define menu again and choose Vectors, then choose Contact Force from the submenu.
6.	Click Run.  Notice that, with the vectors, you can see all the forces acting on the box. Remember to click Stop and Reset.
7.	Click Stop; then, Reset.
8.	Click the incline to select it.
9.	While holding down the Shift key,  click the box to select it.
10.	Open the Window menu and choose Properties. This will give you the properties of the mixed selection that you can edit.
11.	Set the static friction and kinetic friction to 0.
12.	Click Run.  Did the box move faster down the incline? Did the vectors change? Remember to click Stop and Reset. Notice that the frictional force vectors acting on the block are are now different, indicating the change in the mixed object properties.
13.	Click Stop; then, Reset.
	Congratulations! You have learned how to display several forces acting on an object and edit mixed properties on a group of objects. Now, you will add meters to your model so that you can measure the contact forces, not just see them. Steps 1. Create the box and incline. 2. Add vectors and edit mixed properties. 3. Measure the contact forces. 4. Apply external forces.


Step 3: Measure the contact forces

	In this step, you will select the box and the incline and then create a meter, so you can measure the contact forces between them. You should have an open document with the box and incline.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Press the Shift key and select both objects.
3.	Open the Measure menu and choose Contact Force.
4.	Drag the meter away from the box and incline to where you can see it easily.
5.	Click the Fx and the Fy force icons on the side of the meter, so only |F| is active.
6.	Click Run to see what happens.  Click Stop, and then click Reset when you are ready to move on.
7.	Click Stop; then, Reset.
	Congratulations! You have learned how to add a meter and how to modify the information it displays. In the next step, you will apply external forces to your model. Steps 1. Create the box and incline. 2. Add vectors and edit mixed properties. 3. Measure the contact forces. 4. Apply external forces.


Step 4: Apply external forces

	In this final step, you will use the Force tool in the tool bar to apply an external force to the box.  You should have an open document with the box and incline.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Click the Force tool in the toolbar.
3.	Drag from the center of the box down along the incline.  Use this picture as a guide.
4.	Double-click the Force constraint.  Its Properties window opens on the desktop.
5.	Click Rotate with body  in the Properties window.
6.	Click Run to see what happens.  Click Stop, and then click Reset when you are ready to move on.
7.	Adjust the external force to have the box sit on the incline without moving. Remember to click Stop and Reset after each test.  Depending on the size and direction of the external force, the box will behave differently. To adjust its value, drag the force’s "tail" to give a new length or a new direction. A shorter length means less force is applied; a longer length means a larger force. If the force gets too small,  you can use its Properties window to make refined changes.
8.	Click Stop; then, Reset.
Try This	Apply what you have learned to do the following:  Position the external force in different directions. How does this affect the contact force?  Change the frictional forces on the box and incline. Do you have to change the external force to keep the box from moving? Can you remove the external force completely? Change the angle of the incline. How do  the displayed vectors change? Feel free to experiment with what you have learned!
	Congratulations! You have created a complex simulation and learned how to display, measure, and control different aspects of it. Suggested Explorations Change the mass of the box. How will this change the forces acting on it? How do I change body properties?  Change the value of gravity to see it affects your simulation. How do I change gravitational values? Related Topics How do I create a control?


Step 1: Create a ball and set its initial velocity

	In this first step, you will create a ball and a ceiling to set up your basic model.
1.	If you have an existing model open, close it now.  Then, open the File menu and choose New. or If you have an empty document open, you are ready to get started.
2.	Open the View menu and choose Workspace, then choose Grid Lines from the submenu. The grid lines will help you align the objects.
3.	Click the Circle tool in the toolbar.
4.	Draw a small circle near the bottom of the workspace. The circle is a "circular mass," but we’ll call it a ball.
5.	Click the Rectangle tool in the toolbar.
6.	Draw a rectangle across the top of your workspace at least three gridlines above the ball.  Use the grid to help you. We will call this rectangle a ceiling.
7.	Click the Anchor tool in the toolbar.
8.	Click the ceiling with the Anchor cursor. The ceiling is anchored to the background, so it won’t move in the simulation.
9.	Click the ball to select it.
10.	Open the Window menu and choose Properties. or Double-click the object.
11.	Set the vertical velocity (Vy) to 10m/s.
12.	Click Run to see what happens.  Click Stop, and then click Reset when you are ready to move on.
13.	Click Stop; then, Reset.

To save your model:

1.	Open the File menu and choose Save As.
2.	Locate the folder where you want to save your simulation.
3.	Type the name for your simulation and click Save.
4.	Click Save.
	Congratulations! You have set up your basic model. Your ball should have hit the ceiling and then come back down.   Look at the sample picture and make any adjustments to your model before proceeding.  Next you will add a pause control to your simulation. Steps 1. Create a ball and set its initial velocity. 2. Add a pause control to the model. 3. Add a graph to quantify motion.


Step 2: Add a pause control to the model

	In this step, you will attach a control to your ball so you can change how long it moves. You should have an open document with a ball and ceiling.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Open the Measure menu and choose Time. A time meter appears on your workspace.
3.	Drag the meter to position it so you can see it easily.  You can change the look of the meter by clicking to the left of the meter’s title. You can also turn off parts of the meter by clicking  them.
4.	Click Run. Just as the ball goes out of view click Stop. Don’t Reset yet!
5.	Read the time that your ball was in view and remember this value. You will be using this time to set your pause control. You can reset the simulation now.
6.	Open the World menu and choose Pause Control.
7.	Click New Condition.
8.	Enter the time of that your ball was in view to the right of the > in the Pause when textbox.
9.	Click OK.
10.	Click Run to check out the pause control value.  You may have to adjust the value to get it to pause at the right time. Click Reset before trying again.
11.	Click Stop; then, Reset.
	Congratulations! You have just made your simulation easier to use. You can pause your simulation based on other parameters too.  Be sure to save your work! Steps 1. Create a ball and set its initial velocity. 2. Add a pause control to the model. 3. Add a graph to quantify motion.


Step 3: Add a graph to quantify motion

	In this final step, you will add a graph for you to analyze the ball’s vertical velocity as it moves in the simulation. You should have an open document with a ball and ceiling.
1.	If the model you created in the previous step is  already open, you are ready to get started. or If the model is not open,  open the File menu and choose Open, then double-click the file to open it now.
2.	Click the ball to select it.
3.	Open the Measure menu and choose Velocity, then choose  Y Graph from the submenu.
4.	Position the graph so that it is easy to see.
5.	Click Run to see what happens.  What does the graph indicate? Click Reset when you are ready to move on. During the simulation, the Velocity-Time graph forms a straight line sloping down to the right for an object in free fall. When the ball reaches its highest point, the line crosses the x-axis. If your ball hit the ceiling, you won’t see a completely straight line, but there will be a bend in the graph at that time.
Try This	Apply what you have learned to try the following: Adjust the ball’s initial Vertical Velocty (Vy) so that its speed is zero as it hits the ceiling.  Set the pause control to stop at exactly that point. Does the slope of the graph change? Feel free to experiment with what you have learned!
	Congratulations!  You have learned how to control the duration of your simulation as well as adding a graph to help analyze your model.  Suggested Explorations Change the mass of the ball. Does this make a difference in the simulation? How do I change body properties? Increase the air resistance and gravity. How do I change gravitational values? How do I change the air resistance? Make a floor and see if you can get the ball to bounce between the ceiling and the floor.


model

A model is a computer representation of a real world system that you create to simulate its behavior and study its characteristics.

In Working Model, you define a model using a set of bodies and constraints (for example, motors, springs, and joints).  When you click Run, the bodies and constraints act in their defined ways — usually to produce motion — and create a simulation.

Related Topics

How do I control a simulation?

How do I save a simulation?


Getting Started

Workshop

Working with Bodies

Working with Constraints

Using Forces and Vectors

Defining Your Project’s World

Measuring Your Models

Running Simulations

Enhancing Your Simulations

Tips for Advanced Users

Troubleshooting

Glossary


Getting Started

About

     the guide

     the Workshop projects

What’s new

     with Working Model


Workshop

Workshop projects

     Bouncing a ball

     Swinging a pendulum

     Launching a projectile

     Controlling collisions

     Sliding down an incline

     Tossing a ball


Working with Bodies

About

     bodies

Workshop projects

     Bouncing a ball

How do I

     create a body?

     change body properties?

     change a body’s appearance?

     change a body’s geometry?

     rotate a body?

     anchor a body?

     delete an anchor?

     change a body’s COM?

     control collisions?

Why can’t I

     select points in an object?

     highlight points?

Definitions

     acceleration

     anchor

     angular velocity

     Appearance window

     center of mass

     charge

     circle

     COM

     curved polygon

     density

     elasticity

     energy

     friction

     geometric center

     Geometry window

     initial position/orientation

     initial velocity

     mass

     mass object

     material

     moment

     momentum

     polygon

     Properties window

     rectangle

     square

     Toolbar

     velocity

     weight


Working with Constraints

About

     constraints

Workshop projects

     Swinging a pendulum

How do I

     create a constraint?

     create a joint?

     build a joint from separate pieces?

     break a joint apart?

     create a pulley?

     create gears?

     change constraint properties?

     delete a constraint?

     hide a constraint?

     find constraint connections?

Why can’t I

     drag a point or a constraint?

Definitions

     actuator

     Appearance window

     constraint

     damped spring

     damper

     force

     gears

     joint

     motor

     pin joint

     point

     Properties window

     pulley

     rigid joint

     rod

     rope

     rotational damper

     rotational spring

     separator

     slot

     slot joint

     spring

     Toolbar

     torque


Using Forces and Vectors

About

     forces and vectors

Workshop projects

     Sliding down an incline

How do I

     apply a force or torque?

     delete a force or torque?

     change a force or torque?

     display vectors?

     turn off vectors?

     adjust the length of a vector?

     change how vectors look?

Definitions

     Appearance window

     force

     Properties window

     Toolbar

     torque

     vector


Defining Your Project's World

About

     the World frame

Workshop projects

     Launching a projectile

How do I

     change gravitational values?

     change the air resistance?

     activate electrostatic effects?

     change the force fields?

Definitions

     air resistance

     charge

     reference frame

     tracking

     World frame


Measuring Your Models

About

     meters

Workshop projects

     Controlling collisions

How do I

     add a meter?

     modify a meter?

     change a graph’s scale?

     export a meter’s data?

Why can’t I

     drag a control or meter?

Definitions

     Appearance window

     control

     layers

     meter

     Properties window


Running Simulations

About

     simulations

How do I

     control a simulation?

     use the tape player controls?

     save a simulation?

Definitions

     Play bar

     script

     simulation

     simulation history

     Toolbar


Enhancing Your Simulations

About

     simulation enhancements

Workshop projects

     Tossing a ball

How do I

     create a control?

     change a control’s properties?

     change a control’s appearance?

     import data for an input control?

     add menu buttons?

     work with text?

     add pictures?

     link multiple documents?

Why can’t I

     drag a control or meter?

Definitions

     Appearance window

     control

     Coordinates bar

     Properties window


Tips for Advanced Users

How do I

     avoid inconsistent initial velocities?

     best use automatic features?

     build and debug a complex model?

     build complex objects?

     control a simulation’s duration?

     change WM from another application?

     determine the best time step?

     make a simulation run faster?

     minimize collisions?

     prevent objects from penetrating?

     prevent rebounding inelastic collisons?

     prevent simulations from slowing down?

     put a body directly on another?

     put a point on the edge of an object?

     run a long simulation?

     run a simulation unattended?

     select connected objects?

     use formulas?


Troubleshooting

Why can’t I

     select points in an object?

     highlight points?

     drag a point or a constraint?

     drag a control or meter?


Glossary

Definitions

     acceleration

     actuator

     air resistance

     anchor

     angular velocity

     Appearance window

     center of mass

     charge

     circle

     COM

     constraint

     control

     Coordinates bar

     curved polygon

     damped spring

     damper

     density

     elastic

     elasticity

     electric charge

     electrostatics

     energy

     force

     force field

     friction

     gears

     geometric center

     Geometry window

     inelastic

     inertia

     initial position/orientation

     initial velocity

     joint

     kinetic energy

     layers

     mass

     mass object

     material

     menu button

     meter

     moment

     momentum

     motor

     pin joint

     Play bar

     point

     polygon

     potential energy

     projectile

     Properties window

     pulley

     rectangle

     reference frame

     rigid joint

     rod

     rope

     rotational damper

     rotational spring

     Rotate tool

     script

     separator

     simulation

     simulation history

     slot

     slot joint

     spring

     square

     Text tool

     Toolbar

     torque

     tracking

     vector

     velocity

     weight

     World frame


Simulation Warnings

Working Model has an automatic warning feature to alert you about possible problems in your model.  If activated, these warnings appear while the simulation is running, or even before the first frame is calculated.  These warnings could indicate a serious problem with your model, and the simulation result may be incorrect, if not catastrophic, if the simulation is continued without corrections.

The following is a list of selected simulation warnings.  You can turn on or off these warnings in the Accuracy dialog box.  The High Accelerations and High Velocity warnings are controlled by a checkbox titled "Inaccurate Integration" in the Accuracy dialog.

•	High Accelerations Warning

•	High Velocity Warning

•	Redundant Constraint Warning

•	Initial Mass Overlap Warning


 High Accelerations

This warning dialog appears when bodies undergo accelerations large enough to change velocity by 1/5 the amount of the high velocity threshold in one simulation step.

High accelerations can be an indication that the system needs a smaller or variable (Accurate mode) time step to be accurately simulated.  High accelerations can result from forces which are extremely large.

Try reducing the value of Time Step in the Accuracy dialog box for better accuracy.


 High Velocities

This warning dialog appears when bodies have a velocity large enough to move 20 times the maximum error distance in the current simulation step.  This behavior may cause a loss of accuracy, or irregular collisions.

Try reducing the value of Animation Step in the Accuracy dialog box to decrease the distance traveled by bodies between each frame.


  Redundant Constraints

This warning dialog appears when more constraints are being used than are necessary to constrain a specific object's motion. For example, a body with several pin joints between it and the background is redundantly constrained.

One or more of the constraints will be ignored.


 Inconsistent Constraints

This warning dialog appears when conflicting constraints are being used, and the situation cannot be solved. For example, when a mass driven by a constant velocity motor hits a second, anchored mass.

One or more of the constraints will be ignored.


 Initial Mass Overlap

This warning dialog appears when two or more masses overlap by more than the set tolerance, and the bodies are not connected by joints or designated as Do Not Collide.

When two overlapping bodies collide, they may cause physical instability in the simulation.  The overlapping bodies should be designated as Do Not Collide by selecting the bodies and using the Do Not Collide option in the Object menu.  If the bodies need to collide and the message appears at frame 0, then the bodies need to be moved apart so they no longer overlap;  if the message appears at a later frame you should reduce the time step or set accuracy to Accurate mode.

The warning message indicates one pair of bodies that are overlapping (such as body[5] and body[11]).  If your model has more than one pair of bodies overlapping each other, the warning message will keep appearing at RUN until all overlapping bodies are moved apart or set as Do Not Collide.

To check whether a set of bodies could collide with each other, simply select the set of bodies, and look under the Object menu.

 If you see a checkmark beside "Collide", the bodies could collide with one another when they come in contact.

 If you see a checkmark beside "Do Not Collide", the bodies will penetrate one another when they come in contact.

 When more than two bodies are selected and the collision property is not uniform for the bodies, minus ("-") signs appear beside "Collide" and "Do Not Collide"; some bodies collide while others do not.

If you wish to configure your model so that it has only a few pair of collidable bodies:

1.	Choose Select All in the Edit menu.

2.	Choose Do Not Collide in the Object menu to turn off all collisions.

At this point, none of the bodies will collide with others.

3.	Shift-select a set of bodies that can collide, and choose Collide in the Object menu.

This way, you are turning on collision for selected bodies, and Working Model can save computing time since the model has fewer potential collisions to look for.