Tugging on a Chain: Earth-Moon Connection Explored

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Discussion Overview

The discussion explores the hypothetical scenario of tugging on a chain extending from the Earth to the Moon, examining the implications of rigidity, shock wave propagation, and material properties in two distinct scenarios: one where the chain is attached to the Moon's surface and one where it is unattached. The conversation touches on concepts related to physics and material science.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant proposes that tugging on the chain would result in a shock wave traveling up the chain at approximately 5 km/s, suggesting that detection of this wave would take a significant amount of time.
  • Another participant states that no material is completely rigid, indicating that both chains would initially stretch when tugged, and that the far end would remain stationary until the shock wave reaches it.
  • It is noted that the time it takes for the shock wave to travel is at least 1.5 seconds, but could be longer due to the speed of sound in the material being less than the speed of light.
  • A participant mentions the challenges of finding a material that would not stretch or break under its own weight, referencing concepts related to space elevators.
  • Another participant comments on the speed of sound in metal, agreeing with the previous claim but not verifying the specific number.

Areas of Agreement / Disagreement

Participants generally agree on the non-rigidity of materials and the behavior of the chain under tension, but there are varying interpretations regarding the implications of shock wave propagation and the specifics of material properties.

Contextual Notes

The discussion does not resolve the complexities of material behavior under extreme conditions or the exact nature of shock wave propagation in this hypothetical scenario.

OSalcido
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Imagine a solid chain from the Earth to the moon's surface (which I believe is 1.5 light seconds away).

Now Imagine two scenarios.
First scenario is that the chain is attached directly to the moon's surface.
Second scenario is the chain is unattached.

What happens if I tug on the chain in both scenarios? If information travels at the speed of light, how does the universe know whether I should be able or unable to pull the chain at that moment?
 
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What happens if I tug on the chain in both scenarios?
A shock wave creeps up the chain with a speed of ~5km/s. A highly sophisticated interferometer at the moon might have a chance (well, not really) to detect it one day later.
 
The answer is that no material is completely rigid and both the chains will initially stretch (by the same amount) when tugged. For the time it takes the shock wave to get to the other end of the chain (A minimum of 1.5 seconds but in practice a lot longer because shock waves in a material travel at the speed of sound in that material) the chains will both behave the same, with the end you are tugging moving while the far end is stationary.

In practice it would be difficult to find a material that will not stretch and break under its own weight even before tugging. Google for "space lift" or "space elevator" to see a related subject.
 
ah so that's what they mean when they talk about rigid bodies

thank you both :)
 
Btw, that 5km/s that Ich was talking about is the speed of sound in metal (didn't check the number, but it sounds reasonable).
 

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