Pulling Force: Use this tool to give body elements constant external pulling forces during Run mode. To attach the pulling force vector, click on the target body, then drag out the vector in the direction and to the length you desire. The pulling force vector appears as a thin black line pointed away from the body.

You can later change the length and direction of the force vector by resizing it, or by setting the strength (magnitude, in N) and direction (up, right, down, left) in the vector's Properties Box. You can attach multiple force vectors to one body.

You can also choose the pulling force type. The force can be of type:

• constant in both time (the duration of the simulation run) and location;
• distance, which means that the force is only constant over a certain distance (set by the sliding scale) after you click the Run button.
• duration, which means that the force is only constant for a certain duration (set by the sliding scale) after you click Run.

Since bodies can only move in either the horizontal or vertical directions (never along a diagonal), you cannot place horizontal force vectors on a body with vertical force or speed vectors. The reverse is also true.

In the Properties Box, you can also set the label on the force vector (default is Pull) and show (or not show) the vector's label, and length (i.e., magnitude or strength). You can also opt to show (or hide) the force vector during Stop mode, Run mode, or Pause mode.

With the Select tool, you can move the force vector along the surface of a body or change its direction. If you hold down the Shift key, you can rotate the force vector 180 degrees using the arrow keys.

Normal, Friction, and Gravity Forces: Normal, friction, and gravity forces are objects with their own Properties Boxes. For these forces, you can change their labels and their show properties.

The strength and direction properties for the normal and friction vectors are disabled (the gravity vectors have no strength and direction properties). These forces are calculated during Run mode by the simulator, so changing their strength and direction (after enabling the properties) has no effect.