CBSE Class 8 Answered

As we know pressure is a measure of the force exerted on a surface per unit area.

It is expressed in units of force per unit area, such as pascals or N/m² as per S.I system.  

i.e.,

The pressure exerted by an object on a surface is calculated by dividing the force applied by the area over which that force is applied.

The size of the surface can affect the pressure, so expressing pressure in terms of force per unit area allows us to compare the relative pressures exerted by different objects or forces on different surfaces, regardless of the size of the surfaces.

Or in simple terms, the reason we express pressure in terms of force per unit area is because the amount of force that is applied to a surface can vary depending on the size of the surface. For example, if we applied a force of 100 N to a surface with an area of 1 m², the pressure would be 100 N/m². If we applied the same force to a surface with an area of 0.1 m², the pressure would be 1000 N/m². By expressing pressure in terms of force per unit area, we can compare the relative pressures exerted by different objects or forces on different surfaces, regardless of the size of the surfaces.