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Dave, You are without doubt a modern-day Aristotle. >> How about initial condensation on the bottom of the pan when you fill it with cold water, or else a tiny pin-hole somewhere, to give little water droplets and tiny gas explosions (steam) as the driving force? This would levitate the pan slightly so it would be mounted briefly on a virtually frictionless bearing, and then would be able rotate a bit to try to neutralize its undoubted out-of-balance state (not possible to exactly balance a lumpy old pot). Next droplet, next explosion, 10 per second. Or, with steam still the driving force, the frequency might be some natural vibration of the pot and contents, or of the pot and its handle (try over- or under-filling it to change the frequency, and gluing up the handle). >> Try filling it the night before with water and allowing this to equilibrate to room temperature (control against external condensation), and then putting it on a layer of paper towel presoaked in copper sulphate solution and thoroughly re-dried (a check for minute leaks -- would turn locally blue -> pink)? -- just a thought. >> Sounds like very inefficient heat -> vapour conversion-- acquire a new pan with a flat bottom? Looking forward to your step-by-step repudiation of these ideas, as usual. Steve, Halifax On 22-Jan-07, at 9:54 PM, David & Alison Webster wrote: > 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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