Momentum Calculator (p = m·v)

Compute linear momentum from mass and velocity. Result in kg·m/s, with a comparison to a typical small car at highway speed.

Inputs

In kilograms (kg). 0.145 kg ≈ a baseball.

In metres per second. 40 m/s ≈ 90 mph fastball.

Result

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General calculation reads

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How to use this calculator

  • Enter the mass of the object in kilograms.
  • Enter the velocity in metres per second.
  • Read momentum in kg·m/s. The breakdown compares to a small car at 100 km/h.

About this calculator

Momentum is mass in motion: the product of an object's mass and its velocity, p = m·v. It is a vector quantity (direction matters) and is conserved in any closed system — that is the principle behind every collision analysis and rocket-propulsion problem. The total momentum before equals the total momentum after, regardless of whether the collision is elastic or inelastic. Impulse (force × time) equals change in momentum, which is why crumple zones and airbags work: they extend the time of a collision, reducing the peak force for the same Δp. Momentum is measured in kg·m/s; the CGS unit g·cm/s is occasionally used in particle physics.

Frequently asked

Is momentum the same as inertia?+
No — inertia is just mass (the resistance to a change in motion). Momentum is mass × velocity, so a stationary object has inertia but zero momentum.
Why does momentum matter in collisions?+
Because total momentum is conserved. If two objects collide, p_before = p_after, regardless of whether kinetic energy is conserved (only true for elastic collisions). This single law explains pool-ball physics, rocket propulsion, and Newton's cradle.
What is the difference between momentum and kinetic energy?+
Momentum scales with v, KE scales with v². Doubling speed doubles momentum but quadruples KE. Both are conserved in elastic collisions, but only momentum is conserved in inelastic ones.
Can momentum be negative?+
Yes — sign reflects direction. Two objects moving towards each other have momenta of opposite sign; their sum can be zero (centre-of-mass frame).
How does this relate to impulse?+
Impulse = force × time = change in momentum. So a 10 N force applied for 2 s produces 20 N·s of impulse, changing the object's momentum by 20 kg·m/s.

Related calculators

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Compute average velocity from total displacement and elapsed time. Result in m/s with km/h and mph conversions.

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