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Definition of momentum\

It is convenient to define a physical quantity called momentum, usually indicated by the symbol p, as the product of its mass m by its velocity \vec{v}

(1)   \begin{equation*} \vec{p} = m \vec{v} \end{equation*}

The momentum is a vector quantity which has the same direction as the velocity of a body.

The unit of measurement of momentum in the SI system is the product of the units of mass and velocity and thus is the kg m/s.

A new form of the Second Newton’s Law\

Newton’s Second Law can be expressed in terms of change in momentum:

(2)   \begin{equation*} \vec{F}<em>{net} = m \vec{a} = m \frac{(\vec{v}</em>{final} -\vec{v}<em>{initial} )}{\Delta t} = \frac{m \vec{v}</em>{final} - m \vec{v}<em>{initial} }{\Delta t} = \frac{\vec{p}</em>{final} -\vec{p}<em>{initial} )}{\Delta t} \end{equation*}

which can be written in the more compact form

(3)   \begin{equation*} \vec{F}</em>{net} = \frac{\Delta \vec{p}}{\Delta t} \end{equation*}