Boyle's Law
At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure.
Formula / equation
p₁V₁ = p₂V₂
Unit
Pa·m³
In depth
Compressing a gas packs the same number of molecules into a smaller space, so they strike the walls more often and the pressure rises in exact inverse proportion. A plot of p against 1/V is a straight line through the origin, and the pV product is constant along any isotherm.
Examples in the real world
A syringe plunger pushed to half its volume doubles the internal pressure; a diver's bubbles expand as they rise.