Finding the momentum of an object is easy if you know the mass of the object and its velocity.  The momentum of an object is a vector quantity that depends on the mass and the velocity of the object.  Since we already used the letter m for mass, we use the letter p to represent the momentum.

Finding the Momentum of an Object

To find the momentum, simply multiply the mass times the velocity.

\(\color{black}{ \vec{p} = m \vec{v}}\)

Note that this is a vector equation. The mass is a scalar.  When we multiply it by the velocity (a vector) the result is a vector quantity.

Since momentum is a vector quantity, it can be broken into components.  As always, we usually choose our coordinate system in a way that simplifies the problem.  If you have an object moving in a straight line, you usually choose that direction to be the x-direction.

Object moving to the right.

Finding the momentum of an object involves multiplying the mass and velocity. The sign of the velocity determines the sign of the momentum.

Stationary object

A stationary object has no momentum because its velocity is zero.

An object moving in the negative direction has negative mmomentum

An object moving to the left has negative momentum because its velocity is negative.

Units of momentum

We simply multiply the mass and velocity of an object to find the momentum.  This means that the units for momentum contain a mass unit and a velocity unit.  If you are measuring in standard SI units, the units for momentum would be kg m/s.

There is no special name or symbol for this unit.  Make sure that you don’t accidentally square the seconds.  That would turn the combination into a newton.  Remember, Newtons measure force.

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