Angular Momentum

Angular Momentum ( L )

Conservation of Momentum• The total angular momentum of a rotating object remains

constant if the net torque acting on it is zero• If the net torque on an object is zero, the total angular

momentum is constant.

Iω = I0ω0 = constant

Example

A child stands on the edge of a rotating merry-go-round. He then starts to walk toward the center. What happens?

Example

Two plates have masses MA = 6.0 kg and MB = 9.0 kg and equal radii of 0.60m. They are initially separated. Plate A is accelerated from rest to 7.2 rad/s in 2.0 s. Calculate a) the angular momentum of A b) the torque required to accelerate A c) Next, plate B, initially at rest, is dropped onto plate A and the two plates the both rotate together. Find the new angular velocity.

Example• A skater has a moment of inertia of 100 kg m2 when his arms

are outstretched and a moment of inertia of 75 kg m2 when his arms are tucked close to his chest. If he starts to spin at an angular speed of 2.0 rev/s with his arms outstretched, what will his angular speed be when they are tucked in?