Definition
A change in the temperature of a gas that occurs when the gas is compressed or expanded, without any heat being added to or taken away from the gas by an outside source.
Plain English
When air is squeezed, it gets hotter. When it is allowed to spread out, it gets cooler. The temperature change happens on its own from the squeezing or spreading, not because anything heats or cools it from outside.
Context Anchor
Seen in powerplant, compression, induction, turbine, and weather discussions where air or gas is being compressed or expanded.
Derivation
From the Greek 'adiabatos,' meaning 'not to be passed through.' The idea is that heat does not pass through the boundary of the gas during the change. Knowing this helps the term make sense: 'adiabatic' literally points to the fact that no heat crosses in or out.
Why Pilots Care
Adiabatic heating is why air gets hot when compressed in an engine cylinder or turbocharger, and adiabatic cooling is why rising air in the atmosphere cools and forms clouds. Understanding this helps explain both engine behavior and weather.
Analogy
A bicycle pump can get warm when you pump hard. The air is being squeezed, so its temperature rises even though you did not put a flame or heater on it.
Grounding Statement
Pump up a bicycle tire quickly and feel the pump get warm — that warmth comes from compressing the air, not from any outside heat source. That is an adiabatic change.
Intuition Check
Do not read adiabatic change as just “any temperature change.” It specifically means the temperature changes because the gas is compressed or expanded, not because heat flows in or out.
Example Sentence 1
The air entering the cylinder is heated by adiabatic change as the piston compresses it on the compression stroke.
Example Sentence 2
As the parcel of air rises and expands it undergoes an adiabatic change and cools.