Momentum Calculator
Calculate linear momentum from mass and velocity.
Can be negative to indicate the opposite direction.
Results update as you type.
How it works
Momentum captures how much motion an object carries, and this momentum calculator finds it by multiplying mass by velocity. The result, reported in kilogram-metres per second, tells you how hard the object would be to stop and how much punch it delivers in a collision. Momentum matters because it is conserved: in any collision or explosion with no outside forces, the total momentum before equals the total momentum after. That single principle lets physicists and engineers predict the outcome of car crashes, rocket launches, billiard-ball collisions, and recoiling firearms without tracking every internal force. A momentum calculator turns raw mass and velocity figures into the conserved quantity that makes those predictions possible. The formula works because momentum is the product of how much matter is moving and how fast it moves, so doubling either the mass or the velocity doubles the momentum. Velocity is a vector, so momentum has direction as well as size; entering a negative velocity here represents motion in the opposite direction, which is essential when adding the momenta of objects moving toward each other. Students, crash analysts, and sports scientists all reach for a momentum calculator to quantify motion precisely.
p = m × v
Momentum is the quantity of motion an object carries, defined as its mass multiplied by its velocity, so a heavier or faster object has more of it. The formula works because momentum measures how much effort is needed to stop the object, and that effort scales with both how much matter is moving and how fast it moves. Because velocity is a vector, momentum has direction too, which is why a sign or direction accompanies the number and why momentum is conserved in collisions.
Source:Standard physics (linear momentum)
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter mass and velocity.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Momentum updates instantly as you type — no button to press.
Frequently asked questions
What units does the momentum result use?
With mass in kilograms and velocity in metres per second, momentum comes out in kilogram-metres per second, the SI unit. There is no separate named unit for momentum as there is for force or energy. If your velocity is in kilometres per hour, convert it to metres per second first by dividing by 3.6, so that the momentum figure is expressed in the standard SI combination.
Why can velocity and momentum be negative?
Velocity is a vector, meaning it has direction, and momentum inherits that direction. A negative value simply indicates motion opposite to whatever you chose as the positive direction. This sign is crucial in collision problems: two objects moving toward each other carry momenta of opposite sign, and adding them, respecting the signs, gives the correct total momentum of the system before impact.
How is momentum different from kinetic energy?
Both describe motion but differently. Momentum equals mass times velocity and is a vector conserved in every collision. Kinetic energy equals one-half mass times velocity squared, is a scalar, and is only conserved in perfectly elastic collisions. Because kinetic energy depends on velocity squared, doubling speed quadruples energy but only doubles momentum, so the two quantities respond differently to changes in speed.
What does conservation of momentum mean?
Conservation of momentum states that when no external force acts on a system, its total momentum stays constant no matter what happens inside it. In a collision, the combined momentum of all objects before impact equals the combined momentum afterward. This lets you solve for an unknown final velocity, and it explains rocket propulsion, recoil, and the way pool balls transfer motion on impact.
Does a stationary object have momentum?
No. If velocity is zero, then mass times velocity is zero, so a stationary object has no momentum regardless of how heavy it is. Momentum exists only while something moves. This is why a parked truck exerts no impact force from motion, yet the same truck at highway speed carries enormous momentum that takes a large force acting over time to stop.