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I did an experiment in my home and I was surprised by the results. I heated a pan without anything in it. After some time it became very hot and I took some water (2 drops) and put it into the pan. It started behaving very strangely. The water is forming droplets, and the droplets are jumping here and there and fizzing and rapidly moving across the pan. When I put more water, then it forms big drops. And the drops are floating here and there like mercury drops. You can see the video here.

What is happening here? Why is the water behaving like this?

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  • $\begingroup$ You'd better describe in words what is happening. The video is quite hard to view. $\endgroup$ – Ruslan Nov 23 '13 at 10:48
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    $\begingroup$ In short, the answer to your question is Leidenfrost effect. $\endgroup$ – Ruslan Nov 23 '13 at 10:50
  • $\begingroup$ @Ruslan The water is forming droplets, and the droplets are jumping here and there. When I put more water, then it forms big drops. And the drops are floaing here and there like mercury drops. $\endgroup$ – Kartik Nov 23 '13 at 10:50
  • $\begingroup$ @Kartik: Yes, that is Leidenfrost. $\endgroup$ – DumpsterDoofus Nov 23 '13 at 15:54
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If the metal pan was cool then you would expect to see water droplets staying in the same place once any original movement had dissipated. You would have a combination of cohesive forces within each water droplet and adhesive forces between the water and metal surfaces.

With the metal having a temperature well above the boiling point of water, the water molecules touching the metal will boil. This has two effects:

  • the gas under the liquid breaks the adhesive forces between the metal and liquid forming a cushion rather like a hovercraft, so the droplets can now move horizontally much more easily than they could without the cushion; this requires the droplets to be small enough for the cushion to be able to hold up the remaining liquid but big enough for the cohesive forces to maintain the remaining liquid as a the droplet

  • the water gas molecules will try to escape round the side of the droplet and (combining with others) will push the droplet. As they escape, the liquid comes back in contact with the metal, producing more gas and maintaining the cushion

The combination of these two effects produce the rapid movement of the fizzing droplets across the pan which you show in your clip

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