2.7 Momentum

2.7 Momentum

We are aware of the fact that moving object possesses a quality by virtue of which it exerts a force on anything that tries to stop it. The faster the object is travelling, the harder it is to stop it. Similarly, if two objects move with the same velocity, then it is more difficult to stop the massive of the two. Newton referred to this property as "momentum", a vector quantity defined as the product of an object's mass and velocity. This term is now called linear momentum of the body and is defined by the relation:

In this expression, $\mathbf{v}$ is the velocity of the mass $m$. Linear momentum is, therefore, a vector quantity and has the direction of velocity. The SI unit of momentum is kilogram metre per second ($\mathrm{kg\,m\,s^{-1}}$). It can also be expressed as newton second ($\mathrm{N\,s}$).