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Hourglass on the Moon

  1. Jan 26, 2009 #1
    Will a sand-filled hourglass flow faster, slower, or the same on the moon as it does here on earth?
  2. jcsd
  3. Jan 26, 2009 #2


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    welcome to PF.
    What do you think, are things heavier on the moon, do they fall faster or slower?
  4. Jan 26, 2009 #3
    Thank you for the reply, and the well wishes. I was thinking that the hourglass is timed by grains of sand passing through a narrow orifice, and only the grain passing through the orifice is in free fall. I thought that perhaps granular flow, and whether the reduced gravity might reduce the compaction of the sand which would allow a faster flow toward the orifice. We may just have to go up there and find out. Thanks.
  5. Jan 26, 2009 #4


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    I think you can consider an hourglass as just objects in free fall.
  6. Jan 26, 2009 #5
    Doesn't it also depend on how fine grained the sand is, and also the radius of the middle portion of the hour glass too?
    I think the slower-hour-glass-in-moon is true only if the sand is freely falling. Here it's controlled. It would be slower - but how slow would depend on the physical properties of the sand and the hour glass.

    When do you completely measure one hour? - when the top portion is empty, or when the bottom portion is full?

  7. Jan 27, 2009 #6


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    It shouldn't, given that these properties remain constant. Since the OP said "an hourglass," we can assume the same hourglass on both the Earth and Moon. Since the change in gravity does not effect the size of the grains or the radius of the chokepoint, only the change in rate of fall should matter.
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