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Movement of glass of water

  1. Aug 5, 2012 #1
    Hello!

    I'm sorry if I'm posting this in the wrong section. I didn't know where else to put this.

    So here's the problem: Sometimes when I put a glass of water after drinking from it on my table (which also has a glass surface), the glass slides a little bit on its own. Sometimes it happens right after I have put it on there, and sometimes it stands still where I left it and slides after some time has elapsed, comes to a stop and slides a relatively smaller distance again later! I've also observed that this only happens when the glass is wet and while, this doesn't happen every time, it has happened enough times to convince me that I'm not hallucinating.

    So, it's just been bothering me what the real cause of the movement is. I'm sure as hell it's not magic.
     
  2. jcsd
  3. Aug 5, 2012 #2
    I've noticed this too - but only for some glasses. I was wondering if it was something to do with the shape of the base of the glass? For example it has never happened to me with a wine glass, or a mug, but a tumbler does do it. I had previously thought there had been trapped air underneath the glass which had managed to escape, moving the glass, but I don't think this is right. Could it be a surface tension thing?

    OK, going to go and experiment...
     
  4. Aug 5, 2012 #3

    Drakkith

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    I've had this happen many times at a local diner. The glasses have a flat bottom and water from condensation builds up on the glass. Eventually enough has fallen down into a small puddle that when you set your glass down you are putting in on a layer of water that allows it to slide with virtually no friction. Combine that with a very slightly tilted table and you have a glass that moves on it's own.
     
  5. Aug 5, 2012 #4
    Is that all it is? I've not been able to replicate it at home today, but I have a feeling the glass moves in a non-consistent direction. Could the movement come from the fluid under the glass readjusting to a uniform thickness?

    Time to go the the pub and try more experiments there.
     
  6. Aug 5, 2012 #5

    Drakkith

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    I'm not sure. My glass always slides towards the edge of the table at the diner.
     
  7. Aug 6, 2012 #6
    Yeah! My glass always slides toward the edge of the table too. I never thought that the table could be tilted, because... it doesn't appear to be, heh. :p

    Thanks Drakkith.

    @Rooted: Let me know if you find something cool with your experiments.
     
  8. Aug 6, 2012 #7

    Drakkith

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    The table doesn't really even need to be tilted. It could be bending very slightly under elbows and such as well. And it doesn't take very much tilt or bending to produce movement when you are floating on a liquid.
     
  9. Aug 7, 2012 #8
    Yes, very reasonable.

    Thanks Drakkith! :)
     
  10. Aug 11, 2012 #9
    My guess is that you have an air bubble trapped under the bottom of the glass, maybe it expands slightly causing the glass to move?
     
  11. Aug 11, 2012 #10

    Drakkith

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    Why would the air suddenly expand? Do you think this is a better explanation than the one I gave already?
     
  12. Aug 11, 2012 #11
    He doesn't mention if its a cold drink or a hot coffee in a glass mug, I've seen plenty of bubble come out from underneath a cup on a wet surface.

    I think both answers are plausible but why do you ask?
     
  13. Aug 11, 2012 #12

    Drakkith

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    I think he was talking about cold drinks since he was saying talking about condensation on the glass.

    I have a hard time believing that gas expansion from a hot drink that is on liquid would cause much. The difference in temperature simply isn't that much. However, I can't say for sure.
     
  14. Aug 11, 2012 #13
    He doesn't use the word "condensation" anywhere in this post!

    He was asking a question and I just threw in possible answer, I don't see the problem with that.
     
  15. Aug 12, 2012 #14

    Drakkith

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    True, but he did say "when the glass is wet", which I took to mean condensation.



    There is no problem. This is a forum and things are open to discussion. I just don't think that a hot beverage is going to cause gas to expand and slide anywhere. But, as I said, I am not sure, as I am only one person and have been wrong plenty of times in the past. If you think differently you could try and convince me otherwise.
     
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