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Momentum Calculator

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Enter any two of mass, velocity, and momentum - the third is calculated automatically.

Momentum Calculator

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Momentum =
40 kg·m/s
Fill in exactly two values, and leave the one you want to solve for blank.

The formula

Momentum (p) = Mass x Velocity
Example

A 5 kg object moving at 8 m/s: momentum = 5 x 8 = 40 kg·m/s.

Step-by-step guide

  1. Fill in any two values - mass, velocity, or momentum - and leave the third blank.
  2. Read the calculated result.

Why momentum is conserved in collisions

Momentum is a foundational quantity in physics because, unlike energy, it's always exactly conserved in a closed system - the total momentum before a collision equals the total momentum after, regardless of whether the collision is elastic or messy and energy-losing. This is why momentum calculations are central to analyzing collisions, from billiard balls to car crashes to rocket propulsion, even in situations where some kinetic energy is lost to heat or deformation.

Common mistakes

Confusing momentum with kinetic energy - momentum scales linearly with velocity, while kinetic energy scales with velocity squared, so the two behave very differently as speed changes.
Forgetting that momentum has direction (it's a vector) - in problems involving multiple objects moving in different directions, sign and direction matter for correctly adding momenta together.

Frequently asked questions

Is momentum always conserved?

Yes, in a closed system with no external forces - total momentum before and after any interaction (like a collision) stays exactly the same, one of physics' most reliable conservation laws.

How is momentum related to force?

Force equals the rate of change of momentum over time - see our Impulse-Momentum Calculator, which directly connects force, time, and the resulting change in momentum.

Why does a heavy, slow-moving object feel harder to stop than a light, fast one?

It depends on which has more momentum, not just speed alone - since momentum scales with both mass and velocity equally, two very different objects can have the same momentum despite very different speeds and masses.

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