Which of the following best describes kinetic energy?

Kinetic energy is defined as the energy that an object possesses due to its motion. This concept hinges on the speed and mass of the object; the faster an object moves and the more mass it has, the greater its kinetic energy. For instance, a moving car or a rolling ball both have kinetic energy because they are in motion.

The other options do not accurately capture the essence of kinetic energy. The first choice refers to potential energy, which is the energy stored in an object based on its position or state. The third choice misunderstands the relationship between energy and mass, as energy can be converted into mass according to the principles outlined in Einstein's theory of relativity, but this is not the primary definition of kinetic energy. The final option describes energy that is not currently being used, which could refer to potential energy or other forms but does not directly relate to kinetic energy, which must involve movement. Thus, the correct answer reflects the fundamental principle that kinetic energy is indeed the energy of motion.