MEPX
Chapter 6 of 13All chapters
  1. 1What physics is
  2. 2Units and measurement
  3. 3Describing motion
  4. 4The laws of motion
  5. 5Forces
  6. 6Energy and work
  7. 7Momentum and collisions
  8. 8Waves
  9. 9Sound
  10. 10Light and optics
  11. 11Electricity and magnetism
  12. 12Heat and thermodynamics
  13. 13Modern physics

Chapter 6 of 13

Energy and work

The currency that is never spent.

Conservation

Energy changes form but the total in a closed system stays the same. A falling ball turns potential energy into kinetic energy, then into heat and sound on impact.

  • Work is force times distance moved along the force, measured in joules.
  • Power is work per second, measured in watts.

Efficiency

No machine turns all its input into useful output; the rest becomes heat. That is why perpetual motion machines fail, and why the second law of thermodynamics is unpopular.