Foucault pendulum string medium

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Discussion Overview

The discussion revolves around the mechanics of a Foucault pendulum, specifically addressing how the string or rope used in the pendulum does not twist with the Earth's rotation. Participants explore this concept through various scenarios, including pendulums at different latitudes and the implications of the pendulum's motion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants express confusion about why the string does not twist despite being attached to a base that is fixed to the ground, suggesting that the entire setup should rotate with the Earth.
  • Others propose that the pendulum bob co-rotates with the Earth, which prevents the string from twisting, as both the bob and the string are rotating around their own axes.
  • A participant suggests starting with a simplified model of a pendulum at the South Pole to illustrate that the string remains untwisted because the bob is co-rotating with the Earth.
  • There is mention of a rigid Foucault pendulum requiring a bearing at the attachment point to allow for free vertical motion, raising questions about what prevents the string from untwisting.
  • Some participants argue that adding swing to the pendulum does not affect the twisting of the wire, maintaining that the mechanics remain consistent across different configurations.

Areas of Agreement / Disagreement

Participants generally express confusion and uncertainty about the mechanics involved, with multiple competing views on how the string behaves under the influence of Earth's rotation. No consensus is reached regarding the explanation of the phenomenon.

Contextual Notes

Participants highlight the need for a clear understanding of the mechanics involved, but there are limitations in the explanations provided, particularly regarding the assumptions about the pendulum's motion and the effects of rotation at different latitudes.

adam.kumayl
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This question is literally driving me crazy. How does the String or rope or whatever is used in a Foucault pendulum not twist with the rotation of the Earth (because the rope is attached to bases that are attached to the ground).

Actually if the bases are attached to the ground, that should be the ENTIRE thing is rotating so how are we able to see the effect?

please if you're going to explain it dumb it down to the most reduced form of an explanation visually because this problem is on my nerves. Thank you in advance!
 
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adam.kumayl said:
This question is literally driving me crazy. How does the String or rope or whatever is used in a Foucault pendulum not twist with the rotation of the Earth (because the rope is attached to bases that are attached to the ground).
What should prevent it from untwisting? With rigid Foucault pendulums you obviously need a bearing in the attachment, that gives the vertical axis free.
 
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I'm sorry I'm not quite clear on the things you described. If it twists it should mess up the motion of the swing, we know that it DOESNt twist..Why doesn't the rope twist?
 
adam.kumayl said:
This question is literally driving me crazy. How does the String or rope or whatever is used in a Foucault pendulum not twist with the rotation of the Earth
To think about that case start with a simplified setup, then add features back to it.

In this case start with a pendulum at one of the Earth's poles, say, the South pole. Also consider first a non-swinging pendulum.

So you have that pendulum bob, suspended above the south pole. That pendulum bob is co-rotating with the Earth. The wire of the non-swinging pendulum will not twist/untwist because the bob is rotating around its own axis, co-rotating with the Earth.

Next step: such a pendulum on any latitude. Let's call that a 'latitudinal pendulum'. Such a pendulum is circumnavigating the Earth. The thing is: just as the polar pendulum bob is rotating on it's own axis, the latitudinal pendulum is rotating on it's own axis. So just as the polar pendulum bob will not twist the wire the latitudinal pendulum will not twist the wire.

Adding swing makes no difference either, not to the polar pendulum and not to the latitudinal pendulum.
(As many have pointed out in earlier threads: on a scientific station located right at the south pole, in the winter of 2001, three guys have actually rigged a foucault setup, in a high staircase. Allan Baker recounts it was tough going; that staircase was unheated.)
 
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