Here's why:
* Closed System: A closed system means that no external forces or torques act on the system. This implies no interaction with the environment that could transfer angular momentum in or out.
* Angular Momentum: Angular momentum is a measure of an object's tendency to rotate. It depends on the object's mass, velocity, and distance from the axis of rotation.
* Conservation: The conservation of angular momentum states that the total angular momentum of a closed system remains constant over time.
Examples:
* A spinning ice skater: When a skater pulls their arms in, their rotational velocity increases. This is because the skater is effectively reducing their moment of inertia (mass distribution), but the total angular momentum remains constant.
* Planets orbiting a star: The planets maintain their angular momentum as they orbit. Their orbital speed and distance from the star adjust to keep the total angular momentum constant.
Important Note: While the total angular momentum of a closed system remains constant, the distribution of angular momentum within the system can change. For example, in the ice skater example, the angular momentum shifts from the skater's arms to their body as they pull them in.
In summary, the angular momentum of a closed system is a conserved quantity. It cannot change unless external forces or torques act on the system.
