Energy definition

"energy is the ability to do work" is the standard definition used in many physics and engineering textbooks.

A more precise statement is:

Energy is the ability (or capacity) to do work.

The reason I said "capacity to do work or cause change" is that many modern physics texts broaden the definition because energy also drives processes that don't neatly fit the classical definition of mechanical work (e.g., heating, radiation, chemical reactions, phase changes). However, for engineering and introductory physics, the classical definition is preferred.

For example:

• Physics/Engineering definition:
  Energy is the ability (capacity) to do work.

• Work definition:
  Work is done when a force causes an object to move through a distance in the direction of the force.

• SI unit:
  Both energy and work are measured in joules (J).