MEPX
Chapter 1 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 1 of 10

Heat and temperature

Two quantities people conflate.

The difference

Temperature measures the average energy of particles. Heat is energy moving because of a temperature difference. A bath at 40 degrees holds far more heat than a cup of tea at 90.

  • Thermal equilibrium is reached when the flow stops, not when energies are equal.
  • Kelvin starts at absolute zero, which is why it is used in the equations.

Capacity

Different substances need different amounts of energy to change temperature. Water has an unusually high heat capacity, which is why it moderates climate and makes a good coolant.