Question

why school bags are provided with broad straps and not with thin straps?

Answer 1

As we know that pressure is inversely proportional to area,
so if the area is increased, keeping the force same, then pressure decreases.
School bags are provided with broad straps as to increase the surface area in contact with the shoulders to decrease the pressure on shoulders.

Answer 2

school bags are provided with broad straps and not with thin straps so that the mass is distributed over a larger area and the child wont feel the pain as it feels when it wears the bag made up of thin straps

if the straps are small the pressure will be exerted in the small region so the child will experience more pain whereas in case of broader straps pressure will act on large area therefore not much pain is experienced