How does a figure skater increase their spin speed?

• A. By extending their arms outward.
• B. By increasing the friction with the ice.
• C. By pulling their arms in to decrease moment of inertia.
• D. By leaning backwards.

Answer: (C)

A figure skater increases their spin speed by pulling their arms in, which decreases their moment of inertia. According to the principle of conservation of angular momentum, when a dancer or skater spins with a fixed total angular momentum, manipulating their mass distribution affects their rotational speed.

When the skater pulls their arms closer to their body, they reduce their moment of inertia because moment of inertia depends on how the mass is distributed relative to the axis of rotation. A lower moment of inertia means that the skater will rotate faster to conserve angular momentum, most evident when the arms are tucked in close to the body.

In contrast, extending the arms outward increases the moment of inertia, which would slow down the spin. Increasing friction with the ice does not contribute to increasing spin speed in a significant way; rather, it could hinder the skater's movement. Leaning backwards has various effects on balance and posture, but it does not directly contribute to an increase in spinning speed like pulling the arms in does.