It’s difficult to hold a school bag with a thin strap because the pressure on the shoulder is significantly increased due to the small contact area. Pressure is force per unit area, so a thin strap concentrates the weight of the bag onto a smaller surface, resulting in higher pressure and discomfort.
Here’s a more detailed explanation:
Pressure and Area:
Pressure is directly related to force and inversely related to area. Pressure = Force / Area.
Thin Strap, Small Area:
A thin strap offers a very small surface area where the weight of the bag (the force) is applied to the shoulder.
Increased Pressure:
When the weight of the bag is concentrated on a small area (the thin strap), the pressure on the shoulder is significantly higher, making it uncomfortable and potentially painful to carry the bag.
Why Wide Straps are Preferred:
Wide straps, on the other hand, distribute the weight of the bag over a larger area, reducing the pressure on the shoulder and making it easier to carry.