How is energy best defined?

Energy is best defined as the capacity of a body or substance to perform work. This definition captures the essence of what energy is, as it describes energy's role in enabling different forms of work to be accomplished. In physics and engineering, energy is recognized as a scalar quantity that allows systems to perform tasks, whether mechanical, thermal, electrical, or chemical.

When we think of energy in practical terms, it can manifest in various forms such as kinetic energy, potential energy, thermal energy, and others, all of which have the potential to do work. For example, the chemical energy stored in fuel can be converted into mechanical energy to power an engine, illustrating the capacity of the fuel to perform work through a process.

The other definitions provided, while related to concepts in physics, do not encapsulate the broad nature of energy itself. The rate of doing work refers to power, which is a measure of how quickly work is done and is thus a derivative concept related to energy. The ability to apply force describes a characteristic of an object's physical properties but doesn't encompass the broader definition of energy. Lastly, mass is a measure of the amount of matter in an object and is not a direct description of energy. Overall, the most accurate and encompassing definition aligns