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Prove the Earth Rotates This Way?

  1. Sep 3, 2007 #1
    Many years ago, as a child, I remember reading about an experiment that was supposed to prove that the earth rotates. The experiment involved a dish of water and small pieces of cork. A slit was cut in a piece of paper, and ground-up cork was allowed to fall through the slit onto the water. This resulted in the cork forming a line pattern on the water. Supposedly, as the earth rotated, the cork would remain stationary in the water, causing the line to rotate over time.

    As I recall, I never got this to work. Thinking about this now, it seems the experiment itself may be flawed. If this really worked, floating plants in a calm lake would also rotate with time. I know that some commonly known experiements (for example, the ability to balance an egg on its end during the equinox) are actually bogus. Is that true of this experiment as well?

    Hodges
     
  2. jcsd
  3. Sep 3, 2007 #2

    Danger

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    Welcome to PF, Hodges.
    I believe that your best approach would be to forget anything that you've been told in the past and start over.
    To begin with, what more evidence does anyone need that Earth rotates other than the sun coming up and down every day?
    And the reason that it rotates is the same as for every other planet (now that Pluto has been demoted). Our solar system evolved from a huge cloud of stuff that was rotating due to internal gravitational interactions. Since angular momentum must be conserved, the masses that became planets all spun faster as they contracted.
     
  4. Sep 3, 2007 #3
    a focoult pendulum shows that the earth is rotating. you can tell the earth is rotating by witnessing water go down a drain and hurricances too
     
  5. Sep 3, 2007 #4

    cristo

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    Woah.. watch it-- you're stepping into a common misconception there.
     
  6. Sep 3, 2007 #5

    Hurkyl

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    The effect is incredibly weak; I'm not entirely sure it's possible to perform this experiment without introducing currents or other effects that would completely overwhelm the Coriolis effect.
     
  7. Sep 3, 2007 #6
    I'm inclined to think such an experiment could work in principle, the cork pattern ought to rotate with the plane of a Foucault pendulum (actually slightly slower due to friction and viscosity). I just set one up, with ground pepper in a breakfast bowl, and I'll see how it looks before the washing up thisarvo..

    EDIT:

    I've changed my mind, since it's well known that water in a rotating bucket will come to rest with respect to the bucket. One problem is that I have no way to make the water inertially-stationary (abuse of language) initially. With a pendulum (or vibrating spring) the initial velocity is decoupled from the inertial rotation, since for a sufficiently short pendulum any initial release-velocity will produce negligible perturbation to the absolute motion of the pendulum.

    Instead, for kicks, I think I'll analyse Wheatstone's similar apparatus.
     
    Last edited: Sep 3, 2007
  8. Sep 3, 2007 #7

    DaveC426913

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    This is a variation on the "water goes down the drain in different directions in different hemispheres" story which is also a myth. Snopes.

    Note that water going down a drain happens in seconds, whereas the other phenomena that have been mentioned happen over a much longer period of time.
     
    Last edited: Sep 3, 2007
  9. Sep 3, 2007 #8

    Hurkyl

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    And thus I don't believe that the experiment can be performed without other factors completely overwhelming the Coriolis effect. :tongue:
     
    Last edited: Sep 3, 2007
  10. Sep 3, 2007 #9
    i just saw photos of clockwise water in the southern hemisphere, and my sink went the same way, in california...

    only under ideal conditions i guess
     
    Last edited: Sep 3, 2007
  11. Sep 3, 2007 #10
    That's a silly belief to hold: read this.

    Do you know, people will invest millions in attempting to detect gravitational waves on earth, when those are thought to produce far smaller effects (if they even exist), which are normally far more overwhelmed by many factors (which are far harder to eliminate than currents in a water basin). Difficult does not imply impossible.
     
  12. Sep 3, 2007 #11

    DaveC426913

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    I see an article that describes an experiment so poorly that either the experiment is flawed or the writeup of it is. It does not say that he same experiment under the same circumstances was performed in each hemisphere with demonstrable results.

    Shaprio got a consistent direction from one bowl, big deal. Did he try the same bowl in the Southern hemisphere? There's too many unaccounted-for variables.

    There is a big difference between "detection" and "macroscopic effect". A big difference.

    No one said you couldn't detect the rotation of the Earth on an inches/seconds scale, just that it simply does not cause water in a bowl to flow in a different direction depending on where the bowl is.
     
    Last edited: Sep 3, 2007
  13. Sep 4, 2007 #12
    Ouch. You criticise our public media channel (ABC), a national hero (Dr Karl), and groups of scientists around the globe (MIT in USA, and our USyd). :mad:

    "It does not say" every technical detail because the short article I linked to was written for a public audience. If you think any specific variable was neglected in the actual experiments, don't you think you should review the technical literature first?

    And shouldn't it be accepted practice, when an individual such as yourself disagrees with aspects of published professional science, to address that disagreement to an expert peer reviewed journal before denouncing the work on a popular website like here?

    In this case your objection is technically invalid. Regardless of whether "he [tried] the same bowl in [both hemispheres]" himself, he does not need to, because his results have been verified by independent groups in various locations around the globe. Welcome to the scientific method: If you don't believe it, then you too can also attempt to replicate the experiment, and it happens to be simple enough that you could afford to do it in your own living room (and later in a hotel room of the other hemisphere).

    By the way, you do realise that the whole main focus of the article was indeed to dispel the myth that Coriolis force dominates bathroom drains? It just sought to do so in an accurate and factual manner, rather than by instead blindly perpetuating an opposite claim that is equally unscientific.
     
    Last edited: Sep 4, 2007
  14. Sep 4, 2007 #13

    DaveC426913

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    Let me get this straight. You put forth a piece of evidence. But when I poke holes in it, you tell me I have no business criticizing what you put forth, I have to read something else and my criticism must be in an official capacity.

    Nice bait & switch.


    BTW, I did explicitly point out that it might not be the experiment that was flawed, it might simply be the article written that does not cover the experiment.
     
    Last edited: Sep 4, 2007
  15. Sep 4, 2007 #14
    Apologies if this came off as a "bait and switch" but I did put it forth not only because I think it is a high credibility source, but specifically because it references work that proves that under controlled circumstances Earth's rotation does determine the flow direction of water from a basin (which was relevant to Hurkyl's contrary statement).

    Do you still think there is a flaw in the evidence?
     
    Last edited: Sep 4, 2007
  16. Sep 4, 2007 #15

    nrqed

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    I have to agree with cesiumfrog here.
    Unfortunately I don't have the references handy but I did read articles in American Journal Of Physics whose point was precisely what cesiumfrog's article mentions: that under usual conditions (eg the toilet in your bathroom, say), the effect is negligible but that under very careful conditions the effect had been confirmed. It required working with large, symmetrical basins, letting the water rest for at least a day (with no air flowing on it, and isolated from vibrations as much as possible) and, critical point, having a steup allowing to remove the plugger in a symmetric way. Under those careful conditions, the effect had been confirmed, in both hemispheres.

    It seems to *me* that it has become as much an urban myth for scientists to claim that "it's all an urban legend because it's simply too weak to observe in any actual setup". In the end, experiments should give the answer.
     
  17. Sep 4, 2007 #16

    DaveC426913

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    I criticize merely because I am very eager to have proof - one way or 'tother - of this. If you could point me at a more comprehensive description of the experimental results, I'd once and for all be able to put this to rest in my own sphere of People I Argue With.



    I do think though that, the one factor I would have like them to not have changed is the dimensions of the bowl. This is not really a demonstration of the "water down a toilet bowl" myth because they've changed some fundamental parameters.
     
    Last edited: Sep 4, 2007
  18. Sep 4, 2007 #17

    DaveC426913

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    No, I just think the article is a bit sketchy on some points. I have no reason to doubt the experiment is flawed, I simply listed it as one of the possibilities.
     
  19. Sep 4, 2007 #18
    Will the Coriolis force affect currents in Lake Vostok? Will it affect flow in a drained sink basin? The answer to both is "no"; because the maximum width of the lake (and thus, clearly any bathroom sink) is less than its Rossby Radius.

     
  20. Sep 4, 2007 #19

    DaveC426913

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    Well, no. Not unless the drained sink basin is placed in a suitably hot blast furnace... :grin:
     
  21. Sep 4, 2007 #20

    AlephZero

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    The half of the article about weather systems so not so much "a bit shetchy" as just plain wrong. He never even mentions the fact that in each hemisphere cyclones always rotate one way, but anticyclones rotate the other way! Living in the UK we get plenty of experience of both of them - and very few of them start from anywhere near the equator either.

    I don't dispute the experiments described were done, and were reputable. In fact I have some memory of hearing about them when I was learning school physics (which was about the same time that they were they were done).

    But since the first part of the article is completely garbled, there's little objective reason to take the end of it any more seriously than the rest.

    But a more interesting thing to do would be calculate the expected rotational speed of the cork from the details given, and see if 0.25 rev/sec is a believable number to get from the Coriolis effect or whether something else must have been involved.
     
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