1. Torque Give me a lever long enough and a fulcrum on which to place it, and I shall move the world. -Archimedes

2. Changing Circular Motion  In uniform circular motion, a point mass rotates around an external axis of radius, r. (Ex a person on a merry-go-round, a sock in a washing machine)  A rigid rotating object is a mass that rotates around its OWN internal axis. (Ex a merry- go-round platform, a revolving door).  To open a door, you apply a force at a distance from the hinges and perpendicular to the door.

3. Torque and force  Torque is a new action created by forces that are applied off-center to an object.  Torque is what causes objects to rotate or spin.  Torque is the rotational equivalent of force. If force is a push or pull, you should think of torque as a twist.

4. Calculating torque  The torque created by a force depends on the strength of the force and also on the lever arm.  The lever arm is the perpendicular distance between the line of action of the force and the axis of rotation.  Torque is calculated by multiplying the force and the lever arm

5. How torque and force differ  Torque is created by force but is not the same thing as force.  Torque depends on both force and distance.  Torque (N·m) has different units from force (N).  The same force can produce any amount of torque (including zero) depending on where it is applied.

6. Calculating the lever arm  Rotational equilibrium can also be used to find the lever arm needed to make two different forces balances.  A cat and boy can balance on a see-saw even though their weights are very different.  To solve this problem, figure out the lever arm needed for the boy’s torque to balance the cat’s torque.  The cat’s torque is 100 N-m, so the boy must sit 0.2 meters from the fulcrum.