Linear momentum

Beginner

Mass times velocity.

Key relationp = mv

Momentum p = mv is a vector measuring quantity of motion. It's what makes heavy, fast things hard to stop.

Worked example

A 1000 kg car at 20 m/s has p = 20,000 kg·m/s.

Common mistake

Momentum depends on velocity, not speed.

In more detail

Linear momentum is the product of mass and velocity, p = mv. It is a vector, and it is conserved in an isolated system.

Bullets have high momentum because of their speed, even though their mass is small.
Sports coaches use momentum to explain why a heavy player is hard to stop.
A bowling ball has more momentum than a tennis ball at the same speed, which is why it does more damage on impact.

Is momentum a force?

No. It is a property of motion, and force is related to its rate of change.

What are the units of momentum?

Kilogram metres per second.

Is momentum a vector?

Yes. It has both magnitude and direction, so two objects moving in opposite directions can have a total momentum of zero.