FIGURE 11-2
-A figure skater is spinning slowly with arms outstretched. She brings her arms in close to her body and her angular speed increases dramatically. The speed increase is a demonstration of
A) conservation of energy: her moment of inertia is decreased, and so her angular speed must increase to conserve energy.
B) conservation of angular momentum: her moment of inertia is decreased, and so her angular speed must increase to conserve angular momentum.
C) Newton's second law for rotational motion: she exerts a torque and so her angular speed increases.
D) This has nothing to do with mechanics, it is simply a result of her natural ability to perform.

Question

FIGURE 11-2 
-A figure skater is spinning slowly with arms outstretched. She brings her arms in close to her body and her angular speed increases dramatically. The speed increase is a demonstration of
A) conservation of energy: her moment of inertia is decreased, and so her angular speed must increase to conserve energy. 
B) conservation of angular momentum: her moment of inertia is decreased, and so her angular speed must increase to conserve angular momentum. 
C) Newton's second law for rotational motion: she exerts a torque and so her angular speed increases. 
D) This has nothing to do with mechanics, it is simply a result of her natural ability to perform.

Quizplus · Accepted Answer

The increase in angular speed is a demonstration of conservation of angular momentum. The skater's moment of inertia decreases as she brings her arms in, but her angular momentum must remain constant. Therefore, her angular speed increases to compensate for the decrease in moment of inertia and conserve angular momentum.

FIGURE 11-2 -A Figure Skater Is Spinning Slowly with Arms Outstretched. She