Linear momentum and its conservation (3.3)

What is the principle of conservation of momentum?

Principle of conservation of momentum - the total linear momentum before a collision is equal to the total linear momentum after, unless the system is acted on by an resultant external force

p_before = p_after

What are external and internal forces?

External forces - forces that act on a structure from the outside e.g. weight

Internal forces - forces that are exchanged by the particles in the system e.g. tension

If there are no external forces in a system it is closed/isolated

What are elastic and inelastic collisions and how can you tell which a collision is?

In an elastic collision the kinetic energy is conserved. The relative speed of approach is also equal to the relative speed of separation

In an inelastic collision the kinetic energy isn’t conserved

In an elastic collision the particles usually don’t stick together and move in opposite directions

In a perfectly inelastic collision the particles stick together

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