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Thread: Coffee

  1. #1 Coffee 
    Forum Freshman BobTheIgnorant's Avatar
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    So today I got to see something quite interesting, and of course it dealt with coffee. I have taken a little bit of chemistry so I had a understanding of how water works and how inter-molecular forces work and so on. So I was playing with my coffee stirring and then pulling the spoon out. Allowing the drops to fall a very short distance from the surface I saw something really neat. It seemed like for a moment there was a hydrophobic interaction between the new drop and the coffee that it just came out of. What was even weirder was the correlation to temperature it seemed. The colder it was the less time or the less weight/mass it could with held. I refilled my cup about three times looking at the interaction, the hotter it was the larger the drops could be put on the surface for a longer period of time. It was very hydrophobic too, the coffee drops balled up and kind of ran on top of the coffee.
    Sorry if this is not precise enough, but could you please tell me the effects of this? From my understanding shouldn't the hotter the water be the less inter-molecular forces there are so it shouldn't be able to keep shape?


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  3. #2  
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    Quote Originally Posted by BobTheIgnorant View Post
    . It was very hydrophobic too, the coffee drops balled up and kind of ran on top of the coffee.
    Sorry if this is not precise enough, but could you please tell me the effects of this? From my understanding shouldn't the hotter the water be the less inter-molecular forces there are so it shouldn't be able to keep shape?
    Has something to do with rabies? jocular


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    Northern Horse Whisperer Moderator scheherazade's Avatar
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    I'm thinking that it would have something to do with the difference in the surface tension of the liquid in the cup and that of the droplets.

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    Brassica oleracea Strange's Avatar
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    I have seen this effect before but don't know much about the physics of it. I guess that the hotter liquid has a layer of vapour that affects how long the drop can stay on the surface? It may make a difference if you take you coffee black or not.

    I was looking for some more info and came across this: Liquid jets bounce along - physicsworld.com
    I had no idea a stream of liquid could bounce in the same way.
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    Forum Freshman BobTheIgnorant's Avatar
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    Thank you very much PhDemon. What you described gives me a very good idea of what goes on between the liquids in the coffee.
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    Fascinating. At present this is high-speed photography of unpredictable phenomena. If it follows the usual course, we'll be someday building machines entirely of gasses and fluids.
    A pong by any other name is still a pong. -williampinn
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    VERY COOL! Pictures and information!
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