How do forces propagate through the chain?

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    Chain Forces
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Discussion Overview

The discussion centers on the propagation of forces through a suspended chain under the influence of gravity, exploring scenarios where the gravitational source or the hook is suddenly removed. Participants are interested in the mechanics of how reactions and changes in tension propagate through the chain in these situations.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions how gravitational force propagates through the chain, suggesting it acts on the entire chain simultaneously.
  • Another participant proposes that if gravity were to disappear, the bottom of the chain would be the first to notice, leading to a loss of tension as a wave propagates upward through the chain.
  • There is a suggestion that two types of waves might propagate through the chain: one related to gravity and another related to tension.
  • Concerns are raised about the effects of the hook's sudden disappearance, with a focus on how the information regarding this change propagates downward through the chain and the potential delay in the bottom of the chain beginning to fall.
  • A participant argues that the chain would experience some deformation, which could affect the propagation of tension, and clarifies that the concept of a gravitational wave in this context is not accurate.
  • References are made to slinky demonstrations to illustrate the propagation of tension in a more elastic medium compared to a chain.

Areas of Agreement / Disagreement

Participants express differing views on how forces propagate through the chain, particularly regarding the nature of gravitational effects and the mechanics of tension. There is no consensus on the exact behavior of the chain under the discussed scenarios.

Contextual Notes

Participants acknowledge that real chains may exhibit deformation under tension, which complicates the analysis. The discussion includes assumptions about the nature of waves and the propagation of information, which remain unresolved.

Fiziqs
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If I have a chain suspended from a hook, such that gravity is pulling it downward, how does that gravitational force propagate through the chain?

What would happen if the gravitational source suddenly disappeared?

What would happen if the hook suddenly disappeared?

What I'm interested in, is how the reaction propagates through the chain.
 
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Fiziqs said:
how does that gravitational force propagate through the chain?
It doesn't. It acts on the entire chain all the time.

Fiziqs said:
What I'm interested in, is how the reaction propagates through the chain.

This might give you an idea:

 
A.T. said:
It doesn't. It acts on the entire chain all the time.
But even if the gravity acts upon the entire chain all the time, it's still a wave propagating through the chain, such that if the gravitational source should suddenly disappear, the bottom of the chain would be the first to be aware of the disappearance, correct? I would assume therefore that there would be no discernible change in the chain other than a loss of tension, as the wave propagated through it. Neither end of the chain should move because there's no force acting upon it. It's simply a matter of the gravitational wave propagating upward through the chain, and tension disappearing. Or would there be two waves propagating upward through the chain, one for gravity and one for tension?

On the other hand, if the hook should suddenly disappear, it's the information about the loss of the hook that has to propagate downward through the chain, this time only in the form of a loss of tension. But in this case the information should propagate at something significantly less than the speed of light. But I'm not sure when the information reaches the bottom of the chain, and when it begins to fall. There should be a delay between when the top of the chain begins to fall and when the bottom of the chain begins to fall. But is this only due to tension, or will the information reach the bottom of the chain before that?
 
Fiziqs said:
I would assume therefore that there would be no discernible change in the chain other than a loss of tension, as the wave propagated through it. Neither end of the chain should move because there's no force acting upon it.
Only if the chain is not stretched at all under gravity.. A real chain would have some deformation, and the relaxation would accelerate the bottom slightly.

Fiziqs said:
It's simply a matter of the gravitational wave propagating upward through the chain, and tension disappearing.
That isn't a gravitational wave

Fiziqs said:
Or would there be two waves propagating upward through the chain, one for gravity and one for tension?
No.

Fiziqs said:
On the other hand, if the hook should suddenly disappear,
That is basically what the slinky videos show in an exaggerated way (slinky is much more stretchable than a chain).
 

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