6.4 Pressure
If a wooden rod has a flat end, it will be very difficult to push it into the ground. On the other hand, if it has a pointed end, it can be easily pushed into the ground. In the first case, the applied force is spread over a large area, whereas in the second case, the force is concentrated on a small area. The force applied on the rod will exert greater pressure in the second case than in the first one.
lightbulbPressure is defined as the force exerted normally on unit area of an object.
If F is the force acting normally on a surface of area A, then pressure P on the surface is given by:
P = F / A ......... (6.3)
The area A on which the force acts is usually referred to as the contact area. Equation (6.3) shows that for a certain force, the pressure can be very large if the contact area A is small.
In SI, the unit of pressure is N m⁻², which is called the pascal (Pa).