Preparation:Torque/Lever Arm/Explain It/Qualitative, Torque/Lever Arm/Explain It/Quantitative.

On the next page, you can choose from among five different simulations, all of them illustrating different aspects of the lever arm.

• Lever Arm Demo. This demonstrates the lever arm (in green) corresponding to a force vector (in mustard color) acting at a given point (in blue) and a rotation axis perpendicular to the screen through a point O (in red). The line along which the force is acting is shown as a dotted line. The lever arm is the perpendicular from O onto this line.

  The force vector can be changed by dragging its tip. The point at which the force is acting can be changed by dragging the force vector at some point other than its tip. The location of the rotation axis can be changed by dragging point O.

• Construction Demo. You are taken through the construction of the lever arm in step-by-step fashion. First the line along which the force is acting is drawn, then the perpendicular from O onto this line.
• Do-It-Yourself. You can draw a force vector (after selecting FORCE), draw a dotted line to indicate the line along which the force is acting (after selecting DOTTED LINE), and draw the lever arm as a blue line (after selecting LEVER ARM). The correct lever arm is shown in green at the top left corner as soon as a force vector is drawn. You can drag your blue line to the green line for comparison.

  To delete an element, select DELETE and then click on the element. You also can drag all elements and change the force vector and lines by dragging their ends.

• Zero Lever Arm. A force vector and a point O are given. You can rotate the direction of the force vector around the point at which the force is acting and observe how the lever arm changes. To rotate the vector, click the up or down arrow at ROTATE FORCE.

  You can move the point at which the force is acting in a circle around point O while not changing the force vector itself. Click the up or down arrow at ROTATE POINT. You can observe how the lever arm changes.

  Try to make the lever arm zero by operating either one of the controls.

• Lever Arm Calculation. For background on this simulation see Torque/Lever Arm/Explain It/Quantitative.

  To display the lever arm, select LEVER ARM. Calculate the lever arm from the information provided. Then compare answers by clicking CHECK VALUE. The torque due to the given force will be calculated as well. To check on the definition and calculation of torque, go to Torque/About An Axis/Explain It/Quantitative.

  You can change the force vector, the point where it is acting, and the point O of the rotation axis and practise calculating the lever arm for different configurations.