Eduard-Job-Foundation for Thermo- and Matterdynamics

Experiment 3.4: Compression and Expansion of Air


Air is rapidly compressed with a piston in a cylinder having a thermocouple built in. The piston is held down until the pen has returned to its original position and then the piston is released.

Observation and Explanation:
If air is compressed the gas becomes warmer (phase 1). After a while, the gas cools down because it is not insulated from the cylinder walls and the entropy can flow out of the system into the environment (phase 2). The piston ?s expansion leads to a further cooling (phase 3). Then, entropy begins to flow back and the gas starts to warm up again (phase 4). 

Video (mpg4, 1:27)