6.4 Conservation of Angular Momentum

Describe the behavior of a system using conservation of angular momentum.

• The total angular momentum of a system about a rotational axis is the sum of the angular momenta of the system’s constituent parts about that rotational axis.
• Any change to a system’s angular momentum must be due to an interaction between the system and its surroundings.
  • i. The angular impulse exerted by one object or system on a second object or system is equal and opposite to the angular impulse exerted by the second object or system on the first. This is a direct result of Newton’s third law.
  • ii. A system may be selected so that the total angular momentum of that system is constant.
  • iii. The angular speed of a nonrigid system may change without the angular momentum of the system changing if the system changes shape by moving mass closer to or farther from the rotational axis.
  • iv. If the total angular momentum of a system changes, that change will be equivalent to the angular impulse exerted on the system. TOPIC 6.4 Conservation of Angular Momentum

Describe how the selection of a system determines whether the angular momentum of that system changes.

• Angular momentum is conserved in all interactions.
• If the net external torque exerted on a selected object or rigid system is zero, the total angular momentum of that system is constant.
• If the net external torque exerted on a selected object or rigid system is nonzero, angular momentum is transferred between the system and the environment.