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From the past 3-4 days I have been continuously thinking how tension actually works on atomic level. I have even Googled it many times but I was not satisfied with the answers. Can anyone please help me to understand how does tension actually work when we apply a force on a taut rope.

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Imagine a rope which is one molecule thick and it is fixed at one end to a wall.

With no external forces acting on the rope the molecules which make up the rope are at an equilibrium separation and connected to one another with bonds which can be likened to springs.

Applying an external tensile force at one end of the rope has the effect of increasing the separation between the molecules which make up the rope and hence stretching the bonds (springs) between the molecules until an equilibrium situation is reached such that each molecule has no net force on it.

If the molecule to which the external force is applied is labelled $A$, its neighbouring molecule $B$, the next molecule $C$ etc then, the force on molecule $A$ due to the external force is equal in magnitude and opposite in direction to the force on molecule $A$ due to molecule $B$.
In turn the force on molecule $B$ due to molecule $A$ is equal in magnitude and opposite in direction to the force on molecule $B$ due to molecule $C$.
This sequence continues all the way along the rope until the last molecule in the rope is reached where the force on the last molecule due to the penultimate molecule is equal in magnitude and opposite in direction to the force on last molecule due to the wall.

If the externally applied force is made larger then the bonds between molecules become longer with the net force on each of the molecules which make up the rope being zero.
Those forces between molecules constitute the tension force.

With a normal rope the same argument apples except now the external forces is shared amongst many molecular bonds.

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  • $\begingroup$ Thankyou for replying😊. But, I still have one doubt that when we apply force to pull moleculeA then by Newton 3rd law it will also pull us. So isn't the force that we apply cancels out to be zero ? $\endgroup$ – Just going to love physics Aug 13 '19 at 1:43
  • $\begingroup$ Then there must be a force on “us” due to the ground which is equal in magnitude and opposite in direction to the force on “us” due to molecule $A$ resulting in the net force on “us” being zero. $\endgroup$ – Farcher Aug 13 '19 at 11:03
  • $\begingroup$ Thankyou sir for replying again 😊. But then how the force that we apply is transferred to the other end. Also what is the difference between tension and the force we apply (externally).Sorry for asking so many😔(since I have no option other than to ask to you).hope you reply soon. $\endgroup$ – Just going to love physics Aug 14 '19 at 9:23

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