Final answer:
The Law of Conservation of Angular Momentum states that a rotating body's angular momentum will remain constant unless acted upon by an external torque. This principle applies to systems where external torques are absent, keeping angular momentum conservation intact.
Step-by-step explanation:
The principle that describes the unchanging value of angular momentum in a rotating body unless an external force is applied is known as the Law of Conservation of Angular Momentum. Angular momentum is conserved, which means the initial angular momentum will be equal to the final angular momentum when no external torque acts on a system. This law is the rotational analogue to the conservation of linear momentum, which holds when no external force acts on a system.
For instance, in human motion, the angular momentum would not be conserved when a person pushes off the ground, as the interaction with the environment introduces an external force. However, astronauts aboard the International Space Station, when motionless relative to the ship, will have zero angular momentum. Their bodies will continue to have this zero value for angular momentum as long as they do not push off the sides of the vessel, since no external torques are acting upon them.
Equation 11.8 from physics textbooks often states that the rate of change of total angular momentum of a system equals the net external torque. This defines the conditions under which angular momentum is conserved for any system with net angular momentum, including rigid bodies.