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Thread: Moon vs Earth

  1. #1
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    Moon vs Earth

    So I was wondering a couple of things

    1- I have often heard that people weigh less on the moon why is that.

    2 - Is it true the moon was once part of earth? If yes how are the shapes so perfectly round.

  2. #2
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    The answer to both the questions has to do with gravity. Massive things have stronger gravity, so since the earth is much more massive than the moon, it has stronger gravity and hence we weigh more.

    About the moon and earth being spheres, planets and stars and even large enough asteroids become spheres because their gravity pulls them into that shape.


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  3. #3
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    For bodies of the same density the surface gravity is proportional to the radius. Since the Earth is more dense than the Moon, its surface gravity is about 6 times as strong while its radius is less than 4 times that of the Moon.

  4. #4
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    Quote Originally Posted by Jens View Post
    About the moon and earth being spheres, planets and stars and even large enough asteroids become spheres because their gravity pulls them into that shape.
    ...greatly helped by the fact that the collision in which the Moon formed from the Earth
    - turned Earth's surface molten, allowing it to flow freely until it assumed its round shape
    - threw a large portion of the mass into an orbiting ring of rocks pebbles and dust, which naturally formed a sphere as it coalesced into the Moon.

  5. #5
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    Quote Originally Posted by Sinbad View Post
    So I was wondering a couple of things

    1- I have often heard that people weigh less on the moon why is that.

    2 - Is it true the moon was once part of earth? If yes how are the shapes so perfectly round.

    Just further to the previous responses, regarding your first question - to make this easier to understand, it's worth understanding what we mean by "weigh less", because sometimes people think this must mean that somehow there is "less of me".

    There is a gravitational attractive force between any two objects that have "mass". So, if we take the two objects of the Earth and me (each with mass), there is an attractive force between me and the Earth. If I step on a scale, that force acts on the springs in the scale and shows a number of (cough, cough), say, 80 kilograms. We call this measure my "weight" but it is really a measure of that attractive force between me and the Earth.

    Now, if I go to the moon, my mass does not change. That is, the amount of "stuff" in me is no different. However, the moon has much less mass than the Earth, so the attractive force between me and the moon is less. If I step on a scale, there is less force acting on the scale and so it shows a lower number. I "weigh" less even though my mass is no different.

    (It's slightly more complex than that, but this is basically the reason).

  6. #6
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    Thank you that makes total sense now. And atleast I know the next time my wife complains about my beer gut I will just tell her Inmay be overweight here but on the moon I am below average in weight. Lol

  7. #7
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    Quote Originally Posted by Sinbad View Post
    Thank you that makes total sense now. And atleast I know the next time my wife complains about my beer gut I will just tell her Inmay be overweight here but on the moon I am below average in weight. Lol
    Yes, I think you’re getting to understand the gravity of the situation.


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