MEPX
Chapter 7 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 7 of 13

Momentum and collisions

Mass in motion, and what survives a crash.

Momentum is conserved

Momentum is mass times velocity, and in any collision the total before equals the total after. That single rule solves most collision problems without knowing the forces involved.

  • A heavy slow object can carry the same momentum as a light fast one.
  • Kinetic energy is not always conserved: in most real collisions some becomes heat.

Impulse

Changing momentum takes force applied over time. Airbags and crumple zones work by stretching that time, which lowers the force the body feels.