When two people pull on a string in opposite directions with equal forces of 10 N, the string remains stationary. The tension in the string is equal to the force applied by either person. In this case, the tension is 10 N.
Why the Answer is Not 20 N?
It’s easy to think the tension should be the sum of the forces (10 N + 10 N = 20 N), but that’s not correct. Tension in a string doesn’t add up like in this case. Instead, tension is the force felt inside the string as it opposes from being stretched.
The string balances the forces on both ends, and the tension is equal to the pulling force from one side, which is 10 N.
What happens when one end of the string is fixed with the wall?
If one end of the string is fixed with the wall and a person pulls it from the other end with a force of 10 N. In this case
- The person pulls with 10 N.
- The wall resists (opposes the string from moving) with 10 N,
Here, the tension in the string is still 10 N, not 20 N or more. Now think that if the second end of the string holds the second person instead of the wall, he is acting like the wall. I.e., he opposes the string from moving.
What happens if one person lets the string go?
If one person pulls the string and the other lets it go. In this case, there will be no opposing force on the second end of the string. So, here the tension in the string in the string will be 0 N.
Real-Life Example
Think about a tug-of-war game:
- If both teams pull equally hard, the rope doesn’t move. The tension in the rope equals the force exerted by one team.
- If one team lets go, the rope flies toward the other team, and the tension becomes 0 N.
This is similar to how tension works in a string when one end is fixed to a wall or when one person stops pulling.
Conclusion
- When a string is pulled by equal and opposite forces of 10 N, the tension is 10 N, not 20 N.
- If one person acts like a wall or the string is attached to a wall, the tension is still equal to the pulling force, 10 N.
Understanding tension helps us see how forces balance in ropes, strings, and even real-world situations like bridges or tug-of-war
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Newton’s third law (The Law of Action and Reaction)
