1. Chapter 11 Rotational Mechanics

2. Torque If you want to make an object move, apply a force. If you want to make an object rotate, apply a torque. Torque = force x lever arm distance Example: 80 N 3 m (80 N) x (3 m) = 240 N*m

3. Lever Arm The lever arm distance is the distance from the fulcrum to a point perpendicular to the applied force.

4. Examples of Lever Arms Find the lever arm in the following examples:

5. Torque = force x lever arm distance Balancing Torques Larger kid sits closer to fulcrum to balance torque

7. Inertia For objects at rest or in motion, they will tend to stay at rest or in motion unless acted on by an outside force Inertia is the tendency of an object to resist a change in its motion Inertia is dependent upon mass.

8. Rotational Inertia The same is true for rotating objects: Rotational Inertia – tendency of an object to resist a change in rotation

9. Moment of Inertia: The resistance of an object to changes in its rotational motion Moment of intertia = (mass)(radius) 2 I = mr 2

11. Angular Momentum Just as an object moving in a straight path has linear momentum, a rotating object has angular momentum. angular momentum = rotational inertia x rotational velocity Angular momentum = I x ω Angular Momentum: The measure of how difficult it is to stop a rotating object Angular Momentum = (mass)(velocity)(radius) L = mvr

12. Law of Conservation of Angular Momentum: If no unbalanced external torque acts on a rotating system, the angular momentum of that system is constant.