How to Calculate Momentum from Mass and Speed

Calculates momentum as p = mass × speed. Mass is in kilograms, speed in m/s, and momentum in kg·m/s.

Explanation

Momentum captures how much motion an object carries, and how hard it will be to stop. It is simply mass times velocity.

p = m v

$p$ is the momentum, in kg·m/s
$m$ is the mass, in kilograms (kg)
$v$ is the speed, in metres per second (m/s)

Momentum matters because it is conserved. In a collision or an explosion with no outside forces, the total momentum afterwards equals the total before, however messy the event was.

Example

The defaults are a mass of 2 kg and a speed of 3 m/s.

p = 2 \times 3 = 6\,\mathrm{kg \cdot m/s}

The momentum is 6 kg·m/s. To bring the object to rest you could push against it with 3 N for 2 seconds, because force times time, the impulse, equals the change in momentum.

Notes

Momentum has a direction. Taking rightwards as positive, a 2 kg object moving left at 3 m/s has a momentum of −6 kg·m/s. The calculator multiplies whatever you enter, so use a negative speed for the opposite direction.

The unit kg·m/s is the same as N·s. One newton applied for one second changes an object's momentum by 1 kg·m/s.

Momentum is not kinetic energy. Double the speed and the momentum doubles, but the kinetic energy $\frac{1}{2} m v^2$ quadruples. Collisions are analysed with momentum; energy budgets with kinetic energy.