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How can water do this?

  1. Jul 20, 2012 #1
    Since I was a little kid I've noticed that when water is splashed on a flat surface, there are usually some 'special' bubbles that I called 'reverse bubbles'. Reverse bubbles differed from the regular kind by their appearance (very bright and shiny) and their motion, (rapid, indicating substantial mass). Oddly, whenever I mentioned this, no one ever claimed to see them! The phenom was especially obvious in stainless-steel sinks and on cars being washed. it was obvious to me that these were bubbles of water instead of air; the mystery was how this was possible. Anyway I recently got a digital camera with a high-speed mode video and decided to capture some of my reverse bubbles to show to an oblivious world. Upon examining my recording I found something amazing (to me). The 'bubbles' were in fact not bubbles but little spheres of water rolling along like glass marbles! So now I'm even more bewildered. The balls of water skitter along very quickly and usually last less than a second, but they are definitely little spheres of water rolling along across a layer of water (?) To eliminate the idea of surface tension holding them together I spread a thin layer of soap (dishwashing liquid) across the surface; if anything the effect is enhanced! I'm posting this here, risking scorn and derision for treating a well-known thing as a new discovery because I want answers and haven't been able to find any! I put the video on YouTube and can provide a link if anyone's interested.


    Many thanks
     
    Last edited: Jul 20, 2012
  2. jcsd
  3. Jul 20, 2012 #2

    Danger

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    Welcome to PF, Amigajoe.
    I've never noticed such a thing in a regular spill, but water always "balls up" and skitters around when dropped onto a hot surface such as a frying pan. The surface instantly evaporates, and the resultant steam layer insulates the rest of the ball.
    The spherical shape of those, and yours, must come from surface tension so the reaction to an added surfactant puzzles me greatly.
     
  4. Jul 20, 2012 #3

    OmCheeto

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    I noticed this type of behavior with a fluid after I'd heard about the Leidenfrost effect. Only the surface was colder than both the boiling point of the fluid, and colder than the liquid. So I have a supplementary theory.

    But I'll let others chime in before I discuss my amateurish discovery. :wink:
     
  5. Jul 20, 2012 #4
    Yes, I've heard of (and seen)the hot skillet effect and that's the most common response I've gotten when asking about this. Not it.
    Here, look at the video I shot and you tell me.
    This clip stars at 120fps, then changes to normal speed (30fps) to show how fast they move.

    This clip is recorded at 240 FPS and the spherical nature of the water droplets is more obvious as they clearly roll along.

    Unfortunately, as the frame rate increases the resolution drops, so it's not as sharp as I'd like, but the phenomenon is quite clear.
     
    Last edited by a moderator: Sep 25, 2014
  6. Jul 20, 2012 #5

    OmCheeto

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    Ok. I'll give you hint as to what is going on: Thunder!
     
    Last edited by a moderator: Sep 25, 2014
  7. Jul 20, 2012 #6
    Can't be Leidenfrost. You can see the sufrace is covered in the liquid when one of the bubbles breaks. I think you're looking at water-walled bubbles full of air floating on a thin film of water.
     
  8. Jul 20, 2012 #7
    I don't think so. These 'bubbles' are clearly filled with water. Ordinary bubbles can be seen there also; they barely move, while the reverse bubbles shoot out like ball bearings. A bubble of air simply doesn't have the mass to move so quickly. Also the reverse bubbles have a distinctly different appearance, they look like glass and are highly reflective/refractive. They're water.
     
  9. Jul 20, 2012 #8

    OmCheeto

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    Thunder water!
     
  10. Jul 20, 2012 #9

    D H

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    They're called antibubbles. Bubbles on the surface of a liquid are globules of gas surrounded by a thin film of liquid. Antibubbles are globules of liquid separated from the main body of water by a thin film of gas. Antibubbles are weird. They skitter and bounce around rapidly across the surface. Because they are mostly liquid, antibubbles are only slightly less dense than the surrounding liquid. Make the inner liquid of a slightly different substance and the antibubble can even sink.

    Here's an out of this world experiment with antibubbles performed on the International Space Station by astronaut Don Pettit.

     
    Last edited by a moderator: Sep 25, 2014
  11. Jul 20, 2012 #10
    Well...

    Your description sounds kind of like what I'm talking about, but of course it isn't different liquids.
    OK, looking at the Wiki page I see this is correct. So much my new discovery;-(. I see it all the time, why are so few people familiar with this phenomenon?!? 'AntiBubbles', now I finally know what to call them! Thanks! The Wiki page has some good pics and matches my description exactly. Of course it gives no explanation for how it works, which is what I'm really interested in. What keeps the two water surfaces separate, especially with soapy water?
     
    Last edited: Jul 20, 2012
  12. Jul 20, 2012 #11

    OmCheeto

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    I knew I should have waited.... At the microscopic level, we are dealing with planes of liquid, gliding across a surface plane, lubricated like an air based kingsbury thrust bearing, kind of like the air hockey games of old.

    But I still think electrostatics plays a role. :grumpy:

    I'll do more experimenting.......
     
    Last edited by a moderator: Sep 25, 2014
  13. Jul 20, 2012 #12
    I just witnessed this 2 days ago while kayaking and got caught in a rainstorm. The bay was like glass and the rain came and I just watched the little balls of water slip and slide over the surface of the bay. It was so cool. I did not notice the variety shown in the OP video in the sink. And the balls of water were definitely smaller in my experience.

    I just assumed they were balls of water that somehow due to surface tension did not immediately fuse with the bigger body of water. What interested me more is they appeared to be very much the same size. I thought this was due to my inability to possibly see all of them, but there was a definite upper limit to the volume.

    Very happy to see this brought up and discussed. My friend also saw them, we just watched with fascination because they were so easy to see under the light conditions. I knew I had seen them before, but being out in the middle of a bay it was very obvious.

    The electrostatic reasoning of one poster reminds me of the Kelvin water dropper. This device absolutely freaked me out when I first saw it work and the explanation.

    Great timing on this post for me. Great post anyhow.
     
    Last edited: Jul 20, 2012
  14. Jul 20, 2012 #13

    OmCheeto

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    Ah ha! I knew someone should have figured this mystery out long ago:

    Without the electrostatic repulsion forces, there can be no balance. And with no balance, there can be no antibubbles......

    ---------------------------------
    and I guess I can just go to bed then...... :zzz:
     
  15. Jul 21, 2012 #14

    NascentOxygen

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    You see these drops (or bubbles of water) when water drips from the tap into water already in the sink. Now and then there will be a drop (or droplet) that scoots around above the water surface, seemingly unwilling to merge into the anonymity of the greater body of water below.

    Similar phenomenon when you throw a bucket of water over the car to rinse it after a wash.

    Anthropomorphic? Who, me??
     
  16. Feb 19, 2013 #15
    im looking for ways to produce these spheres in diameters of 10 feet to 30 feet in diameter..any suggestions or hurdles to look for?
     
  17. Feb 20, 2013 #16

    sophiecentaur

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    Things like this tend not to 'scale'.
    Which do you think would 'win' at that size - electric or gravitational forces?
     
  18. Feb 20, 2013 #17
    we are looking for a balance between the two
     
  19. Feb 20, 2013 #18
    I think what you are observing is this:

    This video has more but please ignore everything they say, it is wildly misleading:


    They claim it is an air film separating the drop from the water (Probably due to the laminar flow Prandl layer which prevents mixing and slows down air movement)
     
    Last edited by a moderator: Sep 25, 2014
  20. Feb 20, 2013 #19
    I have noticed these 'antibubbles' too. I noticed these antibubbles when I was washing dishes. Thinking they might be due to the soap, I tried to reproduce them using normal water. They could be reproduced both using normal water and with a thin film of water on top of a stainless steel surface (the sink).

    A few interesting properties of these antibubbles: Their refraction index is much larger than normal bubbles, indicating that the bubbles are completely water. The bubbles move fast over the surface over the water and deflect off each other, which is characteristic of spinning tops.

    So it looks to me like these are tiny balls of water which are spinning very fast, fast enough to have friction greatly reduced and for the water to float easily on top of the other water.

    So my question is this:

    If you can have this sort of effect with tiny balls of water, whats to stop a solid which has a great amount of spin from doing the same thing. Furthermore, if this kind of effect is possible with fluids, couldn't we use the same idea to make something float in air?
     
  21. Feb 21, 2013 #20

    NascentOxygen

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    I notice lots of these balls of water running everywhere when I'm hosing the car when washing it.
     
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