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Whenever the velocity and the mass of the body are more, the impact of a force is more. A new physical quantity termed "linear momentum" is defined to quantify the impact of a force exactly. It measures the impact of a force acting on a body.

The multiplication of mass and velocity of a moving body provides the magnitude of linear momentum. Linear momentum is a vector quantity. It acts in the direction of the velocity of the body.

$\begin{array}{l}\mathit{Linear}\phantom{\rule{0.147em}{0ex}}\mathit{momentum}\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}\mathit{mass}\times \mathit{velocity}\\ \\ p\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}m\times v\end{array}$

Linear momentum is expressed by the letter '\(p\)'. It helps to measure the magnitude of a force.

Linear momentum is directly proportional to the mass of the object and also its velocity. Thus the greater an object’s mass or, the greater its velocity, the greater its momentum.

The unit of momentum in the S.I. system is $\mathit{kgm}{s}^{-1}$, and in the C.G.S. system, its unit is $\mathit{gcm}{s}^{-1}$.

For example, a \(1\ kg\) model aeroplane, travelling due south at \(1\ m/s\) in straight and level flight, will have a momentum of \(1\) $\mathit{kgm}{s}^{-1}$ due south measured with concerning the ground.