1. Rotation Notes (Part 2)

2. Rotational Inertia Remember the law of inertia: Objects in motion tend to stay in motion. The same idea can be applied to rotation…

3. Rotational Inertia (cont.) Objects rotating tend to stay rotating. also: The greater the mass, the greater the inertia. Rotational inertia is similar… “The further the bulk of the mass is from the axis of rotation, the greater the rotational inertia.”

4. Concept Questions… Why do bikes have spokes? Why is an Aerobie better than a Frisbee? Golf clubs

5. Angular Momentum Once again, think of regular old momentum. P = mv If the mass was halved, the speed doubles. L Right Hand Rule: If your fingers point in the direction that the wheel spins, your thumb points in the direction of the angular momentum.

6. Angular Momentum For angular momentum… L = mvr If the radius is decreased, the velocity is increased, so momentum is conserved!!! http://www.butler.edu/physics/as102/homework/homework10/angmom.gif

7. Angular Momentum Rotational Stability – It’s conservation of angular momentum! Why it is easier to balance on a bike when moving… Spiral on a football keeps the football aerodynamically sound. Rifle – same deal Gyro’s

8.  = F ┴ ·r Units: N·m Torque DOOR HINGE

9. Chivalry vs. Practicality  Carrying a suitcase… the job is easier with one on each side. Cars…  Torque Wrench  Pipe Over Wrench  Engine Torque Wrestling… Torque