The principle of conservation of angular momentum states that in a closed system with no external torques acting on it, the total angular momentum remains constant. This principle applies to various physical scenarios, such as spinning objects or celestial bodies in motion. For example, when an ice skater pulls their arms in while spinning, they decrease their moment of inertia, resulting in an increase in their rotation speed to conserve angular momentum. This law is fundamental in physics and is applicable in mechanics, astrophysics, and engineering.