 |
 |
Squeaking sand
Name: Jim Keenan
Status: N/a
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993
Question:
When walking across wet sand it will sometimes squeak. Why?
Replies:
This case might be similar to chalk squeaking on a blackboard.
In that case, the chalk is vibrating against the blackboard. In any case,
something must be vibrating in order to create sound. Since there are only
the sand and your feet involved here, the sand would have to be the object
vibrating.
John Hawley
I did not have access to some wet sand to walk on, so instead I
got a bowl of sand from the parking lot to experiment with. And the sound of
"walking" one's fingers on dry sand is qualitatively very different from that
using wet sand. The dry sand produces a kind of a dull, crunchy sound; the
wet sand makes a crisper, louder) sound. One is tempted to guess that the
spectrum of the wet sand sound has more high frequency component than that of
the dry sand sound. The behavior of the sand in the two cases is also
distinctly different: dry sand moves laterally "out of the way" much more
readily than the wet. Water and sand have a great affinity for each other; it
is amazing how well wet sand "sticks together". I speculate that the water
holds the sand grains so tightly together that, under shear (from being
stepped on) they rub hard enough against each other to produce more high
frequency sound, resulting in the squeak. Or perhaps dry sand also squeaks,
but the air in between the grains dampens the sound, whereas water transmits
it. It is also clear that the effect depends on the fineness of the sand;
this will not happen with, say, wet gravel, and I doubt it would happen with
wet powdered sand.
R.C. Winther
Click here to return to the Physics Archives
| |
Update: June 2012
|
|
