What is the definition of energy in physics?

The definition of energy in physics is best captured as the capacity of a physical system to do work. Energy is a fundamental concept in physics that represents the ability of a system to exert influence over other physical systems or to produce changes. This encompasses various forms of energy, such as kinetic energy (the energy of motion), potential energy (stored energy based on an object's position or configuration), thermal energy, and others.

When a system has energy, it can perform work on another system, which is often quantified as force applied over a distance. The concept of work involves transferring energy, resulting in motion or changes in the physical state of matter. Thus, this definition emphasizes the functional role of energy in causing changes in the physical world. Without energy, no work could be accomplished, making it a crucial element in understanding different physical processes.