1. Chapter 11
Rotational Mechanics

2. Torque Force produces acceleration Torque produces rotation
Torque = f x l (lever arm)
Only forces perpendicular to the lever arm contribute to torque
Units: N·m

3. Torque

4. Torque Examples: Prying a lid off a can w/ a screwdriver
turning a nut w/ a wrench
opening a door
doorknob at the edge vs. doorknob at the center

5. Balanced Torques Examples: Seesaw f L = F l
ex: Where would a 600 N boy have to sit in order to balance a 200 N girl who sits 3 m from the fulcrum?

6. Balanced Torques Examples: Scale Balances
ex: Suppose that a meterstick is supported at the center, and a 20 N block is hung at 80 cm. Another block of unknown weight balances the system at the 10 cm mark. What is the weight of the second block?

7. Torque and CG When your base is not below your cg, there is a torque.
Force is required to launch any projectile
If the direction of force is through the cg, the force moves the object as a whole

8. Torque and CG
If the force is off center, the object will rotate about its cg

9. Rotational Inertia
An object rotating about an axis tends to keep rotating about that axis
Resistance to changes in its rotational motion

10. Rotational Inertia Forces change linear motion
Torques change rotational motion
Depends on mass and its distribution
greater the distance between mass and axis, greater rotational inertia

11. Angular Momentum Linear Momentum = inertia of motion ρ = mv
Angular Momentum = inertia of rotation*velocity
mvr
(radius-how far from the center is the mass)

12. Conservation ofAngular Momentum
Ice Skater
arms tucked in = arms extended
mrV = mRv