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Effects of gravity on different elements

  1. Feb 6, 2014 #1

    Hopefully this is the right place for this question.

    I'm wondering whether a 100lb ball of lead would roll down a ramp (assuming a 35 degree slope) at the same speed as 100lb ball of copper.

    Would there be a difference in force while they are rolling down?

  2. jcsd
  3. Feb 6, 2014 #2


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    Might be interesting to watch...

    Last edited by a moderator: Sep 25, 2014
  4. Feb 6, 2014 #3
    Thanks CWatters..

    I do understand that with no 'interference' the two would fall at the same speed.

    But would the larger contact area of the copper ball on the ramp surface be enough to affect results (here on earth)?
    Last edited: Feb 6, 2014
  5. Feb 6, 2014 #4


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    This kind of experiment has been done many times in many different ways, going back to Galileo. The "effect of gravity" (acceleration due to gravity) depends only on the mass of the object, not the material it is made of.
  6. Feb 6, 2014 #5


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    Any difference could potentially change the results but it might be a small. If the balls are different sizes (which they would be as they have different densities) then rolling resistance or air drag might be different and that would change the results.

    If you eliminate every possible difference (same mass, size and rolling resistance and EDIT: Moment of inertia) so that they are the same except for the element that are made from then no, they would both roll down at the same speed.

    How small a difference counts as different? Both lead and copper are electrical conductors and they have different conductivities. On earth they would be moving through the earths magnetic field and that might affect the results - but it would be an exceptionally small effect that is hard to detect.
    Last edited: Feb 6, 2014
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