It is difficult because a thin strap puts a large pressure on a very small area of your shoulder, so it feels like it is “cutting” into you and becomes painful to hold.

Why is it difficult to hold a school bag having a strap made of a thin and

strong string?

Quick Scoop

When a bag has a thin, strong string as a strap, all the weight of the bag is concentrated on a very small area of your shoulder or hand.

Since pressure equals force divided by area, the same weight (force) on a smaller area creates much higher pressure, which feels painful and hard to carry.

The Core Physics Idea

  • Pressure formula :
    Pressure is given by Pressure=ForceArea\text{Pressure}=\frac{\text{Force}}{\text{Area}}Pressure=AreaForce​.
  • In this situation:
    • Force = weight of the school bag (same whether the strap is thin or broad).
* Area = area of contact of the strap with your shoulder.
  • A thin string has very small area , so even a normal-weight bag exerts large pressure on your shoulder.

Result: more pressure → more pain → difficult to hold.

What You Actually Feel

Students often describe it like this:

“When I carry my bag with a thin string, it feels like the strap is digging into my skin.”

That happens because:

  • The weight is concentrated on a narrow line instead of being spread out.
  • This causes:
    • Red marks or dents on the shoulder.
* Soreness or pain after a short time.

* A “cutting” sensation if the bag is heavy and the string very thin.

Thin vs Broad Strap (Easy Comparison)

Here’s a simple comparison in HTML table format, as requested:

html

<table>
  <tr>
    <th>Type of strap</th>
    <th>Contact area on shoulder</th>
    <th>Pressure for same bag weight</th>
    <th>Comfort level</th>
  </tr>
  <tr>
    <td>Thin, strong string</td>
    <td>Very small area[web:1][web:3][web:5][web:7][web:9]</td>
    <td>High pressure (force ÷ small area)[web:1][web:3][web:5][web:7][web:8][web:9][web:10]</td>
    <td>Painful, feels like cutting into skin[web:1][web:3][web:5][web:7][web:8]</td>
  </tr>
  <tr>
    <td>Broad, padded strap</td>
    <td>Large area on shoulder[web:1][web:3][web:5][web:7][web:9][web:10]</td>
    <td>Low pressure (force ÷ large area)[web:1][web:3][web:5][web:7][web:8][web:9][web:10]</td>
    <td>More comfortable, easier to carry[web:1][web:3][web:5][web:7][web:8][web:9][web:10]</td>
  </tr>
</table>

Short NCERT‑style Answer (For Exams)

  • It is difficult to hold a school bag having a strap made of a thin and strong string because the area of contact with the shoulder is very small.
  • Since pressure is inversely proportional to area, a small area produces large pressure on the shoulder, causing pain and discomfort.

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