In this chapter, we will study mass and weight, and their differences.
Mass
Each body is made up of matter. The total amount of matter contained in a body is called mass. In classical physics, we assume the mass of an object remains constant.
Mass is a fundamental physical quantity and a scalar quantity. Its SI unit of measurement is kilogram (kg) and its CGS unit is gram (g). Their relation is
\begin{equation} \rm 1 kg = 1000 g \end{equation}
It is better to define mass as the measure of inertia of a body. Let us imagine a pen and a heavy tank. When we apply the same magnitude of force on both bodies, it is relatively easier to move the pen but difficult to move the heavy tank. Thus, the pen possesses less inertia and the heavy tank possesses more. Hence, we conclude that the mass of the heavy tank is more than that of the pen.
Weight
Weight is the force with which a body is attracted towards the centre of the Earth.
Weight is a derived physical quantity. Its SI unit of measurement is Newton (N) and its CGS unit is dyne (d). Their relation is
\begin{equation} \rm 1 N = 10^{5} dyne \end{equation}
Mathematically,
\begin{equation} \rm W = m \cdot g \end{equation}
It is a vector quantity. Because it is a vector, the weight of a body may be positive, negative, or zero. For a body whose mass is greater than zero, its weight depends upon the magnitude of g (acceleration due to gravity) at the site of measurement.