What is defined as the rate at which work is done?

The correct answer is power, which is defined as the rate at which work is done or energy is transferred over time. In the context of physics, power quantifies how quickly energy is converted from one form to another or how quickly work is performed.

Power is typically measured in watts, where one watt equals one joule per second. This means that if you do one joule of work in one second, you are exerting a power of one watt. Understanding power as a measure of work done over time is crucial in various engineering and scientific applications, as it allows for the analysis of machines, engines, and other systems in terms of their efficiency and performance.

The other concepts mentioned in the choices—force, work, and energy—all play significant roles in physics but do not define the rate at which work is done. Force refers to a push or pull acting upon an object, work is the result of a force applied over a distance, and energy is the capacity to do work. Power integrates these concepts but focuses specifically on the speed of work performance, making it the relevant term in this case.