Momentum is mass times velocity — simple until you need to solve for the missing piece. Enter any two of p, m, or v and get the third instantly, with full working shown.
A momentum calculator lets you instantly find the momentum of any moving object using the fundamental physics formula p = mv, where mass is measured in kilograms, velocity in meters per second, and the result in kilogram-meters per second (kg·m/s). Momentum is one of the most important quantities in mechanics because, unlike energy, it is always conserved in any interaction between objects — a property that makes it essential for analyzing collisions, explosions, and any scenario where objects push or pull on each other.
This calculator is fully flexible: enter mass and velocity to find momentum directly, or enter momentum alongside mass or velocity to solve for the missing quantity by rearranging the formula. That makes it equally useful for basic physics homework and for reverse-engineering problems, such as determining how fast a vehicle was traveling based on the momentum transferred in a collision.
Momentum calculations appear throughout physics, engineering, and everyday life: automotive engineers use momentum conservation to analyze crash dynamics, rocket scientists rely on it to calculate propulsion (a rocket expels mass backward to gain forward momentum), sports scientists study momentum transfer in tackles and swings, and safety engineers design airbags and crumple zones around the impulse-momentum relationship. Because momentum depends linearly on both mass and velocity, it behaves very differently from kinetic energy — a distinction that has major implications for how collisions and impacts are analyzed.
A 1,000 kg car is traveling at 20 m/s (about 72 km/h). Its momentum is p = 1,000 × 20 = 20,000 kg·m/s. If this car collides head-on with an identical stationary car and they lock together (a perfectly inelastic collision), conservation of momentum means the combined 2,000 kg mass must move at 20,000 ÷ 2,000 = 10 m/s immediately after impact — half the original velocity, since the total momentum is shared between double the mass.
The momentum value from this calculator tells you how much 'quantity of motion' an object carries — and, by extension, how difficult it would be to stop or how much force would be involved in bringing it to rest over a given time. Unlike kinetic energy, momentum scales linearly with both mass and velocity, meaning a massive slow-moving object can carry just as much momentum as a lighter, fast-moving one. When comparing your result to the reference table, notice that momentum doesn't follow the same intuitive 'faster means more dangerous' pattern that kinetic energy does. A slow-moving freight train car has enormous momentum despite its low speed, simply because its mass is so large — this is precisely why massive vehicles like trains and ships require enormous distances and forces to stop, even at modest speeds. If you're solving a collision problem, remember that the total momentum of the system is always conserved — this makes momentum the more reliable tool for analyzing collisions compared to kinetic energy, which is only conserved in the special case of perfectly elastic collisions.
Enter any two values (mass, velocity, or momentum) to calculate the third.
| Object | Mass | Velocity | Momentum |
|---|---|---|---|
| Walking person | 70 kg | 1.4 m/s | 98 kg·m/s |
| Sprinting person | 86 kg | 12 m/s | 1,032 kg·m/s |
| Cyclist + bicycle | 90 kg | 7 m/s | 630 kg·m/s |
| 9mm bullet | 0.008 kg | 380 m/s | 3 kg·m/s |
| Car at highway speed | 1,500 kg | 27.8 m/s | 41,700 kg·m/s |
| Freight train car (slow) | 80,000 kg | 5 m/s | 400,000 kg·m/s |