Preparation: Torque/About An Axis/Explain It.

On the following page you can choose from among five simulations related to torques about an axis.

• Qualitative Demonstration. You can make up to three forces act on a square object (click A or B or C and then draw a force vector) and observe the magnitude and sign of the net torque by clicking the PLAY button and observing the rate and sense of rotation. Also, the value of the net torque is printed out.

  The simulation assumes that there is a rotation axis through a point O perpendicular to the screen. You can drag point O to a different location, which can be outside the square object, and observe the effect this has on the torque.

  You can stop and resume a rotation. You can change force vectors after resetting the simulation. To erase a force vector, select the eraser and then click on the force vector, in that order. To change a force vector, drag its tip. To change the point at which a force is acting, drag the vector at some point other than its tip.

  When selecting the LEVER ARM button, the lever arms associated with all forces will be shown in green. Clicking the button again will hide the lever arms.

• Four Torque Calculations. It is shown how to calculate a torque by using
• either the lever arm,
• or the force component perpendicular to the line OA from point A at which the force is acting to point O,
• or all of the following: magnitude of force, distance OA, and sine of angle between force vector and displacement O to A,
• or the scalar components of the displacement vector from O to A and the force vector.