What is an example of a system exhibiting conservation of angular momentum?

What is an example of a system exhibiting conservation of angular momentum?

• A. A spinning ice skater pulling in arms
• B. A car coming to a stop at a red light
• C. A ball rolling down a hill
• D. A pendulum swinging back and forth

Answer: (A)

The system that best exemplifies the conservation of angular momentum is the scenario of a spinning ice skater pulling in their arms. This situation clearly demonstrates how angular momentum is conserved in a closed system. When the ice skater spins with their arms extended, they have a certain moment of inertia and angular momentum. As the skater pulls their arms in, the moment of inertia decreases. According to the principle of conservation of angular momentum, if no external torques act on the skater, the product of the moment of inertia and angular velocity must remain constant. Therefore, as the moment of inertia decreases (because the skater is pulling their arms in), the angular velocity increases, allowing the skater to spin faster. This change occurs while the total angular momentum remains unchanged, illustrating the concept effectively. In contrast, the other scenarios do not illustrate conservation of angular momentum in the same way. For instance, a car coming to a stop involves forces and torque acting on it, leading to a change in momentum rather than conservation. A ball rolling down a hill may experience changes in linear momentum and energy as it accelerates due to gravity, but does not demonstrate angular momentum conservation. Similarly, a pendulum swinging back and forth experiences forces acting on it (like

The system that best exemplifies the conservation of angular momentum is the scenario of a spinning ice skater pulling in their arms. This situation clearly demonstrates how angular momentum is conserved in a closed system.

When the ice skater spins with their arms extended, they have a certain moment of inertia and angular momentum. As the skater pulls their arms in, the moment of inertia decreases. According to the principle of conservation of angular momentum, if no external torques act on the skater, the product of the moment of inertia and angular velocity must remain constant. Therefore, as the moment of inertia decreases (because the skater is pulling their arms in), the angular velocity increases, allowing the skater to spin faster. This change occurs while the total angular momentum remains unchanged, illustrating the concept effectively.

In contrast, the other scenarios do not illustrate conservation of angular momentum in the same way. For instance, a car coming to a stop involves forces and torque acting on it, leading to a change in momentum rather than conservation. A ball rolling down a hill may experience changes in linear momentum and energy as it accelerates due to gravity, but does not demonstrate angular momentum conservation. Similarly, a pendulum swinging back and forth experiences forces acting on it (like