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How can you prove the earth is round?

  1. Jun 15, 2008 #1
    How can you prove the earth is round and not flat using physics


    if anyone can help, thanks!
     
  2. jcsd
  3. Jun 15, 2008 #2

    arildno

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    1. You can't "prove" anything in physics.

    2. The negation of "being flat" is not "being round"; rather, the negation is "being curved".

    First off, the facts that, aside from bumps, valleys, mountains, etc. we generally have the impression that the Earth is "flat", we would have exactly the same impression as long as the curvature of the Earth was sufficiently small, but, crucially, non-zero.

    Thus, we have no evidence whatsoever in favour of the hypothesis that the Earth is "flat".

    Furthermore, we DO have lots of evidence that is far easier to read as evidence for the "curved" proposition, the one already known in antiquity is that of the horizon, how ships appear/disappear there.

    On a flat Earth, the image of the ship would gradually decrease in size as its distance grows, but NOT that the lower parts of it disappeared from view.

    How ships actually disappear or appear at the horizon is, however, fully consonant with the "curved"
    hypothesis.
     
  4. Jun 15, 2008 #3

    russ_watters

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    Is taking a photograph of it physics?
     
  5. Jun 15, 2008 #4

    This could be a combination of perspective effect and atmospheric refraction causing objects to appear or disappear from the bottom up at the vanishing point.

    I have been told this is purely perceptual. a good telescope with sufficient zoom will change the observer's perspective and restore the ship's hull back in full view. This would not be possible if the shop was beind a "hill of water". The fact that a telescope can restore a half-sunken ship demonstrates that the ship is not traveling behind a convex sea.


    - Oh and photos are not sufficent evidence. anyone can manipulate a photo.
     
  6. Jun 15, 2008 #5

    arildno

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    That wasn't an available option prior to the 20th century, so I chose to post the option that has been available since ancient times.

    Not that I disagree with photographic evidence..:smile:
     
  7. Jun 15, 2008 #6

    Vanadium 50

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    But nobody can manipulate what they tell you?

    You have a pretty unusual idea of what constitutes good evidence and what does not.
     
  8. Jun 15, 2008 #7

    arildno

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    And you might just be deluded and brainwashed into thinking you are speaking English, whereas in reality, you are speaking Fulfulde.
     
  9. Jun 15, 2008 #8
    Measuring shadows at different locations?

    I seem to remember that this was one of the first experiments for answering the question.
     
  10. Jun 15, 2008 #9
    hmmm...nope, im pretty sure i'm speaking english. sorry...:uhh:
     
  11. Jun 15, 2008 #10

    siddharth

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    The math, please?

    Knowing the distance to the ship, and the temperature of the air at different heights, one can calculate how refraction occurs. Similarly, if you know the height of the mast, and the velocity of the ship, and observe the rate at which the mast drops, you can verify the radius of the earth.

    Right, there's an international conspiracy among different goverments which have launched satellites or sent astronauts into space :uhh:

    Look at the moon during a lunar eclipse, when there are no clouds. Or, take a jet to a different latitude and look at the night sky. Then, there's also Newton's law of gravity, looking at other planets through telescopes, foucalt's pendulum, etc.

    Absolutely. That was Eratosthenes's brilliant experiment.
    www.youtube.com/watch?v=0JHEqBLG650
     
    Last edited: Jun 15, 2008
  12. Jun 15, 2008 #11

    arildno

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    That doesn't count, your confidence might just be the result of an EFFECTIVE brainwashing.
    :smile:
     
  13. Jun 15, 2008 #12

    russ_watters

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    That's just plain wrong.
    Fair enough. If this is just plain a matter of belief, then there is no scientific content here and nothing to discuss.

    I find it odd that you would post on a physics site that you want a question answered without physics. You should see that that doesn't fit with the purpose of this site.
     
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