Momentum 2

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Elastic and Inelastic Collisions

Elastic collisions conserve kinetic energy. Inelastic collisions do not conserve kinetic energy. Momentum is conserved in both.

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Elastic collision

  • In an elastic collision, momentum and kinetic energy are conserved.
  • Conservation of momentum:
    • Momentum before = momentum after
  • Conservation of kinetic energy:
    • Kinetic energy before = kinetic energy after
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Inelastic collision

  • In an inelastic collision, momentum is conserved but kinetic energy is not.
  • Conservation of momentum:
    • Momentum before = momentum after
  • Kinetic energy is not conserved:
    • Kinetic energy before ≠ kinetic energy after
    • Some of the original energy is dissipated (lost) as heat or other types of energy.
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  • An explosion is simply a collision in reverse.
  • Explosions are inelastic processes as the kinetic energy of the system always increases.
  • The kinetic energy of the fragments comes from the internal energy of the system.

Momentum and Safety

If an object which has a lot of momentum is made to stop suddenly, then a large force is required because of the change in momentum.

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Safety features

  • Cars have safety features such as seat belts, air bags and crumple zones that absorb kinetic energy in collisions.
    • These features reduce injuries to the people in the car by absorbing energy when they change shape.
    • They increase the time taken for the change in momentum to happen, reducing the forces involved.

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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