Pressure:

You are familiar with the concepts of force and pressure from your school physics. To appreciate the difference between these two quantities, think about the following situations.

Why is it that camels walk easily in deserts on sand but for us it is quite difficult? Similarly, when we press a balloon filled with air, it does not burst easily. However, if we prick the balloon with a pin, the balloon bursts easily. The clue to explain these observations is that besides force, we must also consider the area over which the force acts. And, therein lies the concept of pressure which is defined as the ratio of the force to the area on which it acts; that is,

Pressure (P) =  Force (F )/ Area (A)                                                                      . . . (1.4)

The unit of pressure is Nm^-2  or kg m^{- 1}s^-2. This unit is also known as Pascal denoted by Pa.