Re: pinhole Hot Water

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From: pauld@exploratorium.edu
Date: Thu Feb 17 2000 - 04:17:25 PST 

Message-Id: <200002171217.EAA02711@isaac.exploratorium.edu>
From: pauld@exploratorium.edu
Subject: Re: pinhole Hot Water
Date: Thu, 17 Feb 2000 12:17:25 GMT

Hi Ellen

Great observation.
You have rediscovered the leidenfrost efect.
When the plate is hot enough a layer of water vaporizes next to the plate. The
layer of gas is an insulator and keeps the heat from flowing into and boiling
the rest of the droplet of water. The vapor also acts as a frictionless surface
and allows the drop to skitter around. When the plate cools off, the vapor layer
goes away, the drop contacts the surface and the water boils away.

Paul D

> Today, waiting for hot plates to cool off, I dropped some water on them
> and watched it bead and roll, like little marbles. The sound when the
> water hit the hot plate was like a solid hitting. Not until 15 minutes
> had passed and the plate had cooled quite a bit did the water react the
> way I expected -- bubbling and hissing and forming a puddle.
>
> Why?
>
> Ellen Koivisto
>
>
>
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