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Why does water or balls spill out ?

  1. Dec 30, 2015 #1
    I know, this is a very stupid question, but it troubles me the whole day and i can't figure it out.
    Why can't water remains its shape if the cup is being removed and the water will spill all over the table ?
    And if you fill your car with full of small balls and when you open the door of your car, the balls spill out too ?
    Is it Gravity or ? But isn't gravity a downward force ?
    Forgive me stupidity
  2. jcsd
  3. Dec 30, 2015 #2


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    There is a "tendency" for net reduction of potential energy (height above ground level).
  4. Dec 30, 2015 #3


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    What's the matter with gravity being a downward force? Do the balls spill out of your car in an upward direction when you open the door?
  5. Dec 30, 2015 #4
    Nope. That's why I'm asking if it's Gravity.
  6. Dec 30, 2015 #5


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  7. Dec 30, 2015 #6


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    You might be interested in reading about angle of repose.


    Every material has its distinct angle of repose - as any sand castle builder knows.
    I encountered this yesterday, while trying to dig down into the blown cellulose insulation in my attic.

    Water has an AR of 0. :)
    Round balls would have a variable AR, depending on how orderly-stacked they might be.
  8. Dec 30, 2015 #7
    Woah ! Thanks !
  9. Dec 30, 2015 #8


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    Or you could just say Entropy - the universe tends towards equilibrium in all things.
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