Boyle's law
/ BOYL /
Squeeze a gas into half the space at fixed temperature and its pressure doubles. Picture blocking the outlet of a bicycle pump with your finger and pushing down: the harder you compress the trapped air, the more it pushes back.
Precisely: at constant temperature and a fixed amount of gas, pressure is inversely proportional to volume, P V = constant, or P1 V1 = P2 V2. It was discovered by Robert Boyle in 1662.
Why: it is simply the isothermal (constant-temperature) slice of the ideal gas law, the case where T and n do not change. Molecular picture: halve the volume and the molecules strike the walls twice as often, so the pressure doubles.
Block the tip of a syringe with your finger and push the plunger; it feels stiffer and stiffer as the volume shrinks and the pressure rises.
At fixed temperature, P is inversely proportional to V.
Holds only at constant temperature and fixed amount of gas; heat the gas as you compress it and the simple doubling no longer applies.