Physics 12 · Physics · Lesson 2.1
Momentum
- Level
- Grade 12
- Reading time
- 13 min reading
- Review
- Last reviewed 2026-09-03
- Standard
- Accuracy standard
- Errata
Abstract
Mass in motion.
What is momentum in physics?
Short answer
Momentum is the quantity of motion an object has, equal to its mass times its velocity: p = mv. It is a vector, pointing in the direction of motion, measured in kilogram-metres per second (kg·m/s). In a closed system with no external force, total momentum is conserved, which is why momentum is central to analyzing collisions and explosions.
Concept preview
What you will be able to do
- 01Define momentum as and treat it as a vector
- 02Relate force to the rate of change of momentum
- 03Apply conservation of momentum to an isolated system
Why is a slow freight train so much harder to stop than a fast bicycle? Both are moving, but the train has vastly more of what Newton called the quantity of motion — what we now call momentum. Momentum is mass times velocity, , measured in . Because velocity is a vector, momentum is a vector too: it points the same way the object moves, and its direction matters enormously.
School Plan
Momentum
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Related topics
Frequently asked questions
- Is momentum conserved in every collision?
- Total momentum is conserved in any collision with no external force, whether the collision is elastic or inelastic.
- How is momentum different from kinetic energy?
- Momentum (mv) is a vector and is always conserved; kinetic energy (½mv²) is a scalar and is conserved only in elastic collisions.