It is difficult to hold a school bag with a strap made of a thin and strong string because the thin string has a smaller contact area with the shoulder or hand. Since pressure is defined as force divided by area (Pressure = Force/Area), the same force (weight of the bag) applied over a smaller area results in a larger pressure on the body. This greater pressure causes discomfort or pain, making it harder to hold the bag. In contrast, thicker straps distribute the force over a larger area, reducing the pressure and making it easier to carry the bag comfortably.
Key Points
- Thin strap = smaller contact surface area.
- Pressure on shoulder or hand increases with smaller area for the same force.
- Higher pressure causes discomfort and difficulty in holding the bag.
- Wider straps reduce pressure by increasing contact area.
This explains why school bags typically have broad shoulder straps to ease the burden of carrying and minimize discomfort.
