1. Ch. 11 Rotational Mechanics Torque

2. TORQUE n Produced when a force is applied with leverage. n Force produces acceleration. n Torque produces rotation.

3. TORQUE n Torque = Force X Lever Arm n Force must be perpendicular to lever arm. n Torque is increased by – increasing force – increasing length of lever arm

4. A torque is used when… n Opening a door n Turning on a faucet n Tightening a bolt with a wrench n Using a screwdriver n Using a lever

5. Balancing Torques n Torques are balanced when clockwise torque = counter-clockwise torque. n A meter stick is balanced at its center and a 20 N block is hung at the 80 cm mark. Another block is hung at the 10 cm mark. What is the weight of the 2nd block?

6. Toppling and Tumbling n When the CG is not over the area of support, a torque is produced - toppling. n When a force is applied at the CG, no torque is produced. n When a force is applied off center, a torque is produced - tumbling – Object will rotate about its CG.

7. ROTATIONAL INERTIA n An object rotating about an axis tends to keep rotating about that axis. n Rotational Inertia - the resistance of an object to changes in its rotational motion. n It takes a force to change linear state of motion. n It takes a torque to change rotational state of motion.

8. ROTATIONAL INERTIA n Depends on mass and the distribution of the mass. – The greater the dist. between the bulk of the mass of an object and the axis about which rotation takes place, the greater the rotational inertia. n Long objects are harder to rotate than shorter objects

9. ROTATIONAL INERTIA n Not necessarily a fixed quantity n Can be changed by changing distribution of mass – choke up on a bat – bend legs – holding an object n The farther the mass from the axis, the greater the rotational inertia.