MEPX
Chapter 6 of 10All chapters
  1. 1Heat and temperature
  2. 2The first law
  3. 3The second law
  4. 4Engines and efficiency
  5. 5How heat moves
  6. 6Gases
  7. 7Phase changes
  8. 8Thermodynamics in the world
  9. 9The statistical view
  10. 10Time and the universe

Chapter 6 of 10

Gases

Pressure, volume, temperature.

The relationships

For a fixed amount of gas, pressure times volume divided by temperature stays constant. Compress it and it heats; let it expand and it cools.

  • A bicycle pump gets warm for exactly this reason.
  • Aerosol cans cool as they empty because the gas expands.

Why it works

Pressure is countless particle collisions with the walls. Raising temperature makes them faster and more frequent, which is the whole explanation.