For a gas, pressure and volume are inversely proportional. If you keep everything else constant, then as the pressure on a gas goes up, its volume goes down. As the volume a gas occupies goes up, its pressure goes down. Robert Boyle stated the inverse relationship between pressure and volume as a Gas Law. Boyle’s Law says that for a given amount of gas, at fixed temperature, pressure and volume are inversely proportional. P ∝ 1/V. You can write this mathematically as P = k/V
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