Joule (J)

Named after James Prescott Joule, representing energy expended by an electric current.

As the standard SI unit of energy, the joule quantifies mechanical work, thermal heat, and electrical power dissipation across physics and engineering calculations. James Prescott Joule established the equivalence of mechanical work and heat through a famously patient series of experiments in which paddle wheels churned water inside insulated barrels, the resulting rise in temperature demonstrating that motion and warmth were two expressions of the same quantity.