Definition
A gas law stating that, for a fixed mass of gas held at constant volume, the absolute pressure of the gas is directly proportional to its absolute temperature. If the temperature rises, the pressure rises in the same proportion; if the temperature falls, the pressure falls in the same proportion.
Plain English
If you trap a gas in a sealed container so it can't expand, heating it makes the pressure go up and cooling it makes the pressure go down. The hotter it gets, the harder it pushes on the walls.
Context Anchor
Seen in basic aircraft science and maintenance discussions about tires, gas cylinders, and other sealed spaces where pressure changes with temperature.
Derivation
Named after Joseph Louis Gay-Lussac, the French chemist who formalized the relationship in the early 1800s. Knowing the name comes from a person (not a technical term) helps you remember it's just a label, not a clue to the meaning.
Why Pilots Care
Temperature-driven pressure changes in sealed volumes affect tire inflation, fuel tanks, and certain aircraft gas systems.
Grounding Statement
Picture a sealed soda can left in a hot car — the gas inside has nowhere to go, so the pressure climbs as it heats up. That's Gay-Lussac's Law in action.
Intuition Check
Do not assume heated air always expands freely. If the gas is trapped in a fixed-size space, Gay Lussac'S Law says its pressure goes up instead.
Example Sentence 1
The mechanic explained that the high tire pressure reading was due to Gay-Lussac's Law — the tires had heated up during the long taxi.
Example Sentence 2
The law explains why pressure in a sealed oxygen bottle increases when the temperature rises on the ramp.