From the previous equation we see that in the center of mass system, the total linear momentum 'p' is therefore zero:

For a relativistic object the momentum p is equal to:

The product of the mass and velocity is momentum 'p' (which Newton himself called "quantity of motion").

Consider the momentum p of a particle as an example.

Suppose at time t some number of particles all have position r within element dr and momentum p within dp.

At any energy E, the value of the momentum p is found from the conservation equation:

Fixing the energy to be (a negative) constant and solving for the radial momentum p, the quantum condition integral is:

Schrödinger represented the momentum p by a differential operator - which does not commute with the position operator x.

Additionally, mass relates a body's momentum p to its linear velocity v:

Also shown is optical momentum p, tangent to a light ray and perpendicular to the wavefront.