Momentum

This lesson covers momentum, conservation of momentum, and the relationship between force and rate of change of momentum — as required by the Edexcel GCSE Physics specification (1PH0), Topic 1: Key Concepts of Physics. You need to be able to calculate momentum, apply conservation of momentum to collisions and explosions, and explain how safety features reduce forces (Higher tier).

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What Is Momentum?

Momentum is a measure of how difficult it is to stop a moving object. It depends on both the object's mass and its velocity.

momentum = mass × velocity

$p = mv$p=mv

Where:

• p = momentum (kg m/s)
• m = mass (kg)
• v = velocity (m/s)

Key Points

• Momentum is a vector quantity — it has both magnitude and direction.
• The SI unit of momentum is kilogram metres per second (kg m/s).
• The direction of the momentum is the same as the direction of the velocity.
• A stationary object has zero momentum (because v = 0).

Worked Examples

Example 1: A car of mass 1200 kg travels at 25 m/s. Calculate its momentum.

p = mv = 1200 × 25 = 30 000 kg m/s