We have all observed what happens when water drops fall on a hot skillet. Rather than simply boiling off, they skitter around for awhile before disappearing in a puff.
This phenomenon is due to something called the Leidenfrost effect. If you place a drop of water on a surface, it gets flattened and just stays there due to gravity. But when placed on a surface whose temperature is higher than the boiling point of water, a thin layer of water vapor forms almost immediately that partially insulates the drop from the hot surface and also raises it off the surface, making it almost spherical again as well as reducing the frictional forces on it, enabling the drop to move around freely in response to the turbulent air currents that surround it. [Read more...]