Kevin Wampler wrote:
> If you've been on the beach, you've probably noticed that the sand dries 
> out around you foot when you step on it, why is this?  Wouldn't you 
> expect a small puddle of water to form around your foot instead?

Here's the solution as I recall it:





The sand on the beach is actually in a more or less maximally compressed 
state before you step on it.  When you step on the sand, you compress it 
downward slightly, and to allow for this the sand under your foot 
expands outward somewhat.  Since the sand was about as dense as it could 
get at the beginning the end result of this downward compression and 
lateral expansion is that small gaps open up between the grains and the 
sand underneath your foot and its density actually *decreases*.  The 
water that was in that sand thus doesn't fill the whole empty volume 
anymore and drops to below the surface of the sand, causing the top of 
the sand to dry.

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