First Law of Thermodynamics
A statement of universal energy conservation applied to thermodynamic systems, asserting that internal energy change equals net heat added minus work done by the system.
Governing formula
ΔU = Q - W
SI unit
J
In depth
The First Law asserts that heat is a form of energy transfer. Energy added as heat Q either increases internal thermal energy ΔU or performs mechanical work W on the environment.
Examples in the real world
Heating gas inside a cylinder with a movable piston, causing the gas to expand and push the piston outward while raising its temperature.