Peoples Physics Concepts

http://www.ck12.org Chapter 9. Rotational Motion

9.3 Torque

• Calculate torque in various situations.

Students will learn to calculate Torque in various situations.

Key Equations

~τ=~r×~F=r⊥F=rF⊥

Individual torques are determined by multiplying the force applied by theperpendicularcomponent of the moment

arm

Guidance

Torque is equal to the cross product as stated above. In general, one can simplify by saying that the torque is equal

to the force acting on the object multiplied by the perpendicular distance from the application of the force to the

rotational axis. Say you had a seesaw. It is easier to exert torque, get the seesaw to move, if you pushed on the board

near the end rather than near the middle. It is the rotational version of Force.

Example 1

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/1878

Example 2

A 1 m long 2 kg rod is attached to the side of a building with a hinge at one end. The rod is held level by a cable

that makes an angle of 45 degrees with the rod and is also attached to the building above the rod. What is the

tension in the cable? The situation is illustrated in a diagram below.