1. Rolling motion (axis of rotation is moving) Torque Angular momentum Angular momentum is conserved Chapter 11: Angular Momentum part 2 Reading assignment: review for exam Homework :due Monday, Oct. 24, 2005 (an extra week to do it!) Problems:Q3, 1, 2, 3, 6, 9, 11, 14, 20, 36, 43

2. Angular momentum of a particle L… _____________________ r… distance from the origin p… momentum of __________ v…velocity of ______________ Definition: L is ____________ to r and p L has magnitude L = ________

3. Angular momentum of a rotating rigid object We’ll consider an object that is rotating about the _________. The angular momentum of the object is given by: Note that in this case L and  are along the _____________. Also note the analog formula for _________ momentum p = m·v

4. Black board example 12.3 A light rigid rod, 1 m in length, joins two particles – with masses 3 kg and 4 kg at its end. The system rotates in the x-y plane about a pivot through the center of the rod. Determine the angular momentum of the system about the origin when the speed of each particle is 5.00 m/s.

5. Conservation of angular momentum The total angular momentum of a system is _____________ in both magnitude and direction if the resultant external torque acting on the system is zero. If the system undergoes an internal __________________ then: If the object is rotating about a _______ axis (say z-axis), then:

6. ________________ laws

7. Demo A students stands still on a rotatable platform and holds a spinning wheel. The bicycle wheel is spinning in the clockwise direction when viewed from above. He flips the wheel over. What happens?

8. Student on a turn table. A student stands on a platform that is rotating with an angular speed of 7.5 rad/s, his arms outstretched and he holds a brick in each hand. The rotational inertia of the whole system is 6.0 kg·m 2. The student then pulls the bricks inward thus reducing the rotational inertia to 2.0 kg·m 2. (a)What is the new angular speed of the platform? (b)What is the ratio of the new kinetic energy of the system to the original kinetic energy? (c)What provided the added kinetic energy? Black board example 12.4 HW 39