Which of the following best describes kinetic energy?

Kinetic energy is the energy that an object possesses due to its motion. The best example of this concept is a ball rolling down a hill. As the ball moves, it has kinetic energy that depends on its mass and the speed at which it is rolling. The energy increases as the speed of the ball increases, demonstrating how motion translates into kinetic energy.

In contrast, the other options represent objects that are not in motion, and therefore do not exhibit kinetic energy. A book resting on a table and a car parked on the street are both stationary and have potential energy instead, which is energy stored within an object due to its position or condition. A butterfly fluttering in the air does have kinetic energy while it is in motion, but the scenario presented does not emphasize the consistent nature of that motion as effectively as the rolling ball. Thus, the ball rolling down the hill is the most representative example of kinetic energy.