It is difficult to hold a school bag having a thin strap because the pressure on the shoulders is quite large. This is because the pressure is inversely proportional to the surface area on which the force acts. The smaller is the surface area; the larger will be the pressure on the surface. In the case of a thin strap, the contact surface area is very small. Hence, the pressure exerted on the shoulder is very large.
Pressure
Pressure is the force applied by one object to another. Force applied on the object is perpendicular to the surface of the object per unit area. It is represented by P.
The pressure is explained as force per unit area articulated as
P=F/A