Do not confuse units and dimensions. We can use dissimilar units to measure the same physical quantity.

So, for example, you can calculate the mass in units of kilograms, pounds, or even in sair and chatak! In this course we shall always use the MKS or Metre-Kilogram-Second system. When you want to convert from one system to another, be methodical as in the example below:

When you write it out in this manner, note that a variety of quantities cancel out cleanly in the numerator and denominator. So you never make a mistake!