Momentum Calculator
Calculate momentum and impulse, and the force a collision delivers.
Please note: Results use idealised models — point masses, no air resistance, ideal gases and uniform materials. Real experiments deviate. Use these for study and estimation, not for engineering sign-off.
What the Momentum Calculator does
Momentum is mass times velocity — a measure of how hard something is to stop. Impulse is the change in momentum, and because impulse also equals force times contact time, spreading a collision over a longer time reduces the force proportionally. That single relationship is the basis of nearly all impact safety design.
Formula
p = m × vJ = Δp = m(v − u)J = F × Δt, so F = Δp ÷ Δt
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Calculate | one of 2 options | Yes | — |
| Mass | number | Yes | — |
| Mass unit | one of 6 options | Yes | — |
| Velocity | number | In some modes | Shown Calculate is Momentum from mass and velocity. |
| Velocity unit | one of 5 options | In some modes | Shown Calculate is Momentum from mass and velocity. |
| Initial velocity | number | In some modes | Shown Calculate is Impulse and collision force. |
| Initial velocity unit | one of 5 options | In some modes | Shown Calculate is Impulse and collision force. |
| Final velocity | number | In some modes | Shown Calculate is Impulse and collision force. |
| Final velocity unit | one of 5 options | In some modes | Shown Calculate is Impulse and collision force. |
| Contact time | number | In some modes | How long the collision or push lasts. A car crumple zone gives about 0.15 s. Shown Calculate is Impulse and collision force. |
| Contact time unit | one of 6 options | In some modes | Shown Calculate is Impulse and collision force. |
How to use it
- Choose Calculate and Mass unit.
- Enter Mass.
- Fill in the remaining inputs the form shows for your choice.
- Select Calculate.
Worked example
A 1,200 kg car at 100 km/h stopped by a crumple zone over 0.15 seconds.
- Mass
- 1200 kg
- Initial velocity
- 100 km/h
- Final velocity
- 0
- Contact time
- 0.15 s
100 km/h is 27.7778 m/s, so Δp = 33,333 kg·m/s. Over 0.15 s that is an average force of 222,222 N — about 18.9 g on the car.
Frequently asked questions
Why do airbags reduce injury?
They cannot change the momentum you have to lose, but they stretch the stop over more time. Ten times the contact time means a tenth of the force.
Is momentum always conserved?
In a closed system with no external forces, yes — always, in every collision type. Kinetic energy is only conserved in elastic collisions.