Calculating Momentum

Momentum is a property of moving objects, which can be defined using the equation:

  • p = Momentum in kilogram metres per second (kg m/s)
  • m = Mass in kilograms (kg)
  • v = Velocity in metres per second (m/s)

This equation shows three things:

1. An increase in mass leads to an increase in momentum.

2. An increase in velocity leads to an increase in momentum.

3. An object at rest (velocity = 0), will have no momentum.


An object’s momentum depends not just on its mass and speed, but also on its direction. Velocity (speed in a given direction) is a vector quantity, so the momentum also depends on the object’s direction of travel.

  • If an object changes its direction, its momentum will also change.

Since momentum depends on the object’s direction of travel, it can have a positive or negative value. If an object has positive momentum when travelling in one direction, it will have negative momentum when travelling in the opposite direction.

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