smooth balls

Discussion in 'Mind Games' started by machinist, May 4, 2010.

  1. machinist

    machinist Banned Lifetime Supporter

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    OK, check this out..you have two balls


    one is the size of a marble.

    one is the size of the moon.

    each ball is perfectly spherical and smooth.

    each ball is set upon a perfectly flat plane.

    quite naturally each sphere contacts the plane at one point, but is the surface area of contact greater on the larger sphere and less on the smaller sphere, or are they the same?
     
  2. The Earth

    The Earth Om Tare Tutare Ture Svaha

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    at the point of contact its probably the same.. weird
     
  3. The Imaginary Being

    The Imaginary Being PAIN IN ASS Lifetime Supporter

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    A circle has infinite sides, so I am supposing they are both resting on one of these sides (to stop movement). I mean, if the surface area was different, you're talking an astrologically small number I guess.
     
  4. NoxNoctum

    NoxNoctum Member

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    When I read the title the first thing that came to mind was this:

    https://www.youtube.com/watch?v=7sn1RUjbL1g"]YouTube- Dave Chappelle - Balls

    :D
     
  5. thedope

    thedope glad attention Lifetime Supporter

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    A key concept is the center of gravity of a body at rest: it represents an imaginary point at which all the mass of a body resides. The position of the point relative to the foundations on which a body lies determines its stability towards small movements. If the center of gravity exists outside the foundations, then the body is unstable because there is a torque acting: any small disturbance will cause the body to fall or topple. If the center of gravity exists within the foundations, the body is stable since no net torque acts on the body. If the center of gravity coincides with the foundations, then the body is said to be metastable.
     
  6. machinist

    machinist Banned Lifetime Supporter

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    i am still pondering this one
     
  7. eman

    eman Member

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    The moon would touch more of the plane.


    It's simple physics. The plane ceases to be "perfectly flat" as soon as any weight is applied. The larger mass will deform the shape of the plane more than the smaller mass, therefore allowing more surface area to come in contact. If you perform this in space, the mass of the moon will create enough gravity to deform the plane touching it.

    I recall my physics professor emphasizing that if a wire has a weight hanging from it, no amount of force can stretch the wire enough to make it flat.
     
  8. Death

    Death Grim Reaper Lifetime Supporter

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    I was under the assumption that two objects could never really come into contact because of the repulsion of electrons.
     
  9. machinist

    machinist Banned Lifetime Supporter

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    From a geometric point of view this is a simple case of tangency. The spheres rest on a plane just as a line is tangent to a circle. Thus no matter the diameter of the sphere the point of contact is the same.
     
  10. Death

    Death Grim Reaper Lifetime Supporter

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    That;s what i figured. they would warp however in a real life application. but theoretically you are correct sir.
     
  11. machinist

    machinist Banned Lifetime Supporter

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    yeah for comparison purposes I usually take examples to extremes ;)
     
  12. Sir-.-'nOOBalloT

    Sir-.-'nOOBalloT Member

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    I dunno man if we would ignore the force of gravity I think the size of the sphere will very much effects the surface area it will occupancy on the plane thingy. I mean take the needles sharp point and cut it off round it up and put it on a plane, count the atoms that touch the surface or give the charge and repel … Now take a sphere the size of earth and count the atoms that are in effect with the plane? U cant tell me that it will be the same number.


    We are living on a big ass marble and the corner of it that I occupancy is pretty much flat. FFs there was some misconception that the world is flat... take a bigger planet(sphere) and the effect is only magnified.
     
  13. SpacemanSpiff

    SpacemanSpiff Visitor

    Id say the bigger one has a larger contact patch due to its size and its bigger so even though its a sphere its flatter than the marble
     
  14. Death

    Death Grim Reaper Lifetime Supporter

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    I think that if we are talking about tangent points it is either contacted completely flat, like the entire plane is touching, or there is an infinitesimal contact point which is completely immeasurably small. this value wouldnt change with the size of the sphere. does this make sense?
     
  15. Sir-.-'nOOBalloT

    Sir-.-'nOOBalloT Member

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    [​IMG][​IMG]

    This is what i see
     
  16. Sir-.-'nOOBalloT

    Sir-.-'nOOBalloT Member

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    Damit my picture is not showing
     
  17. machinist

    machinist Banned Lifetime Supporter

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    yes this is what makes the question interesting. it's a case of resolution. the larger circle appears to make more contact because it arcs closer to the line over a longer distance, but in fact it is still contacting the same amount as the smaller circle.
     
  18. Death

    Death Grim Reaper Lifetime Supporter

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    that's what I picture too.
     
  19. Winkel

    Winkel Guest

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    This is an interesting question. All material is somehow elastic, and there isn't any material that is completely smooth. Therefore, according to such phenomenon, the contact surface area of the larger ball is greater, since there is more mass to pull down. Everything is elastic.

    But, lets say we have an object that is not elastic. An ultimate, absolutely perfect sphere in any way. Does it have a contact surface at all? Where does the border go? My logic says it should be only one molecule, or even atom. But in metaphysical world of no-atoms, the area of contact should shrink infinitly. Therefore, does it even have an area of contact? Does it float?

    :confused:
     
  20. machinist

    machinist Banned Lifetime Supporter

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    the amount of contact is infinite
     

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