Answer:
When a twirling ice skater brings her arms inward, her rotational speed increases.
Step-by-step explanation:
The principle of conservation of angular momentum says that the angular momentum of a spinning object remains constant, unless the object is acted upon by an external torque. Angular momentum is the product of the object's rotational speed and its moment of inertia. This means rotational speed and moment of inertia are inversely proportional when angular momentum is constant.
The moment of inertia increases with the distance the object's mass lies from its center of rotation. When a spinning skater brings her arms closer to her body, her mass is brought closer to the center of rotation, decreasing her moment of inertia. Friction from the ice and the air do not apply much torque to the skater, so her angular momentum is nearly constant. Thus, her decreasing moment of inertial results in increasing speed of rotation.