Calculation details
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What does this calculator estimate?
A 0.9 kg ball moving at 10 m/s has 9 kg-m/s of momentum: p = 0.9 x 10 = 9 kg-m/s. Momentum is mass times velocity and is conserved in collisions.
- Momentum (kg-m/s) = mass (kg) x velocity (m/s).
- Momentum is a vector: direction matters, not just speed.
- In a closed system, total momentum before a collision equals total after (NIST).
What momentum measures
Momentum is 'quantity of motion' — mass times velocity. It's conserved in isolated systems, which is why collisions and rocket propulsion are analyzed through it: the total momentum before equals the total after.
Limitations to watch for
Momentum uses velocity, so direction matters — opposite velocities have opposite signs. The tool reports magnitude; for analysis you must track direction. Relativistic momentum differs at near-light speeds.
How to use it in practice
Use momentum to analyze collisions: a lighter fast object can match the momentum of a heavy slow one. In impacts, momentum change over time equals the impulse (force × time).
['Enter the mass in kilograms.', 'Enter the velocity in m/s.', 'The tool computes p = m × v.']
How this calculator works
Formula
Momentum p = m × v, where m is mass (kg) and v is velocity (m/s), giving momentum in kg·m/s. Momentum is a vector — it has direction.
Worked example
A 5 kg object moving at 4 m/s has momentum p = 5 × 4 = 20 kg·m/s in its direction of motion.
Assumptions to verify
- Classical (non-relativistic) motion.
- Mass is constant.
- Velocity is the signed vector magnitude entered by the user.
Frequently asked questions
What is momentum?
Mass times velocity: p = mv, in kg·m/s. It's the 'quantity of motion' of an object.
How do I calculate momentum?
Multiply mass by velocity. A 5 kg object at 4 m/s has 20 kg·m/s.
Why is momentum a vector?
Because velocity has direction. Two objects moving in opposite directions have momenta with opposite signs — they can cancel.
What is conservation of momentum?
In an isolated system (no external forces), total momentum before a collision equals total momentum after. It governs billiard balls, car crashes, and rocket thrust.
What's the difference between momentum and kinetic energy?
Momentum p = mv is a vector scaling with velocity; KE = ½mv² is a scalar scaling with velocity squared. Both are conserved in different ways in collisions.
What is impulse?
The change in momentum, equal to force × time. Extending impact time (airbags, crumple zones) reduces the force for the same momentum change.
Does momentum work at high speeds?
Near light speed, relativistic momentum diverges from mv. For everyday objects the classical formula is exact enough.
Cite this tool
BoringToolsKit. “Momentum Calculator.” boringtoolskit.com/momentum-calculator/ (reviewed 2026-08-25). Free to reference in articles, syllabi, and answer posts with a link.
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