Mechanics
Momentum
Pearson Edexcel International A Level Physics
Momentum
momentum = mass × velocityp = m v
- Momentum is a vector, in the direction of the velocity.
- Take one direction as positive: a momentum in the other direction enters every equation negative.
- State the direction of the final momentum or velocity with its size.
Conservation of momentum
- Total momentum before a collision = total momentum after a collision, when no external force acts.
- The forces the bodies exert on each other form a Newton's 3rd law pair: they are equal in size and opposite in direction, so the resultant force on the system is zero.
- Data obey the law when the total momentum remains the same.
Release from rest
Two bodies pushed apart from rest, an explosion or a release:
- The initial momentum is zero.
- The total momentum is zero after the release.
- The bodies have equal and opposite momenta: the momentum of one is opposite in direction to the momentum of the other.
- The lighter body has the greater speed.
Quantities and units
| Quantity | Symbol | Unit |
|---|---|---|
| Momentum | p | kg m s−1 |
| Mass | m | kg |
| Velocity | v | m s−1 |
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