What is defined as the capacity or power to do work?

The choice of energy as the answer is correct because energy is fundamentally defined as the capacity or ability to do work. In physics, work is done when a force is applied to an object and it moves in the direction of that force. Energy can take various forms, such as kinetic energy (energy of motion), potential energy (stored energy based on position), thermal energy, and many others.

The definition of energy encapsulates the idea that it is what enables work to be accomplished. In essence, without energy, no work could be performed, highlighting the intrinsic relationship between the two concepts. Thus, energy serves as the essential resource required to enact change, initiate motion, or carry out any process that involves work.

While other terms like work, force, and power are closely related, they represent different concepts. Work itself is the measurement of energy transfer that occurs when an object is moved. Force is an influence that can change the motion of an object, and power measures the rate at which work is done or energy is transferred over time. However, the fundamental concept that ties these ideas together is energy, which directly describes the capacity to perform work.