Angular momentum and its conservation

Learning objectives

Calculate the angular momentum of a rigid body about a fixed axis as L = Iω and of a point particle as L = rmv sin θ

Relate the net external torque on a system to the rate of change of its angular momentum, and calculate angular impulse as τΔt

State the conditions for angular momentum to be conserved and explain why a spinning skater speeds up when the arms are pulled in, even though no external torque acts

Apply conservation of angular momentum to a collision in which an object strikes and sticks to a rotating body, and explain why linear momentum need not be conserved when a pivot exerts an external force

Compare which of angular momentum, linear momentum and mechanical energy are conserved in a given situation, and justify each answer with reference to the external forces and torques