FYI Blown Away

The process of compression or expansion of a gas so that no heat enters or leaves the system is said to be adiabatic, meaning that heat does not pass in or out. Adiabatic changes can be achieved in two ways. One is by performing the process rapidly, so that heat has little time to enter or leave. Another is by thermally insulating the system from its surroundings.

When work is done on a gas by adiabatically compressing it, the gas gains internal energy and becomes warmer. When a gas adiabatically expands, it does work on its surroundings and gives up internal energy, thus becoming cooler.

A common example of an adiabatic process is the compression and expansion of gases in the cylinders of an automobile. Compression and expansion occur in hundredths of a second, too short a time for heat energy to leave the combustion chamber. Under high compression, as in diesel engines, the temperatures achieved are high enough to ignite a fuel mixture spontaneously, without the use of spark plugs.

You can demonstrate an adiabatic process right now. Blow warm air onto your hand from your wide-open mouth. Now reduce the opening between your lips so the air expands as you blow. Adiabatic expansion causes the air to be cooled.