# Helmholtz free energy

## English

### Etymology

For Hermann von Helmholtz, German physicist.

### Noun

Helmholtz free energy

1. (physics, thermodynamics) A measure of the useful work obtainable from a constant temperature, constant volume thermodynamic system; more precisely, the difference between internal energy (of a system) and the product of its absolute temperature and entropy.
${\displaystyle A=U-TS}$ where A is Helmholtz free energy, U is internal energy, T is temperature, and S is entropy.