2.  Angular momentum is a quantity that tells us how hard it is to change the rotational motion of a particular spinning body  Objects with lots of angular momentum are hard to stop spinning, or to turn  Objects with lots of angular momentum have great orientational stability (think of riding a bike – if you are going fast you will not fall over as easily as when you are going slow)

3.  For a single particle with known momentum, the angular momentum can be calculated using the relationship:  L = r  p  L: angular momentum for a single particle  r: distance from particle to point of rotation  p: linear momentum

4. Determine the angular momentum for the 2 kg particle shown a) about the origin b) about x = 2.0 y (m) x (m) 5.0 v = 3.0 m/s -5.0 5.0

5. Determine the angular momentum for the 2 kg particle shown a) about the origin L = r x p = rmvsinθ L = (2√2 m)(2 kg)(3 m/s)(sin(135°) L = 12 kg  m 2 /s y (m) x (m) 5.0 v = 3.0 m/s -5.0 5.0 θ = 135° r r = (2 2 + 2 2 ) ½ = 2√2 m

6. Determine the angular momentum for the 2 kg particle shown b) about x = 2.0 L = r x p = rmvsinθ L = (2 m)(2 kg)(3 m/s)(sin( 0 °) L = 0 kg  m 2 /s y (m) x (m) 5.0 v = 3.0 m/s -5.0 5.0 θ = 0° r r = 2 m

8.  For a solid object, angular momentum is analogous to linear momentum of a solid object  P = mv (linear momentum)  Replace momentum with angular momentum  Replace mass with rotational inertia  Replace velocity with angular velocity  L = I  (angular momentum)  L: angular momentum  I: rotational inertia  w: angular velocity

9.  The Law of Conservation of Momentum states that the momentum of a system will not change unless an external force is applied  How would you change this statement to create the Law of Conservation of Angular Momentum?  Angular momentum of a system will not change unless an external torque is applied to the system  L B = L A (momentum before = momentum after)

10. A figure skater is spinning at angular velocity  o. She brings her arms and legs closer to her body and reduces her rotational inertia to ½ its original value. What happens to her angular velocity? It will become 2x greater

11. A planet of mass m revolves around a star of mass M in a highly elliptical orbit. At point A, the planet is 3 times farther away from the star than it is at point B. How does the speed v of the planet at point A compare to the speed at point B? m M M V a = 1/3 V b rara rbrb