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Dear All, Jan 22, 2007
I put a saucepan of water onto a piping hot wood stove tonight and a
few minutes later wondered why someone had left the bathroom fan on. The
'fan' turned out to be sound produced by up and down oscillation of the
saucepan about 10 times a second and with an amplitude, at the end of
the handle, of about 3 mm.
The pan has a slightly rounded bottom from having run out of water
several times and, presumably because the rounding is a bit lop-sided,
the pan when oscillating also graduallly turns clockwise as viewed from
above. To start this oscillation, one must set the pan onto the stove
with the handle up ~one cm from level and with no sideways slop of
water. Once the oscillation is started then it continues until the pot
handle rotates around enough to touch the back of the stove or until the
water starts to ping.
Some 12 years ago I saw oscillation of this type involving a larger
pot, which of course also had a rounded bottom, a 7' long steam box that
was balanced on the pot, a period that (I think) gradually increased to
about 4 sec and amplitude that gradually increased to about one foot [at
which point I steadied the box & put a prop under one end].
Having something barely balanced (handle & pot or box much longer
than pot diameter along with rounded pot bottoms) is probably a
necessary condition as is a relatively hot surface but I have yet to
fathom how heat drives the oscillation. Any ideas ?
It does not appear to be related to surface tension effects
because adding a drop of detergent to an oscillating pot had no effect.
It can be difficult to duplicate and may be dependent upon some subtle
configuration of the rounding that changes with recent heating and/or
something related to rate of heat transfer (e.g. a cold pot and a brisk
fire). After starting it 10-15 times without a hitch, after I first
noticed it, I can not now get a sustained oscillation.
Yours truly, Dave Webster, Kentville
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