Why do metal pots wobble on the stove?
james_gifford
I was just cooking dinner and noticed the pot rocking on the element.
It was probably wobbling at about 5-10Hz. I remember seeing this
before and wondering why it did it. The water was well below boiling
temperature and their were no bubbles forming on the surface of the
pan. The vibrations seemed to happen while the pot was heating up, and
settled down once the pot got hot. Weird!
Any guesses?
James Gifford
<James....@anu.edu.au>
Katie Schwarz
I think I've seen this too. Maybe the slight movements of thermal
expansion in the heating element jostle the pot and start it wobbling.
(What exactly causes the "ticks" heard as a stove heats or cools? Is it
expanding in irregular jumps rather than continuously?) Any suggestions
on how to test this hypothesis?
Katie Schwarz
ka...@physics.berkeley.edu
Patrick P. E. Esch
: Katie Schwarz
: ka...@physics.berkeley.edu
Just a wild guess, but can it not be that this is a
relaxation (oscillator) phenomenon where stress builds
up to a point where the "holding force" (friction, ...)
is overcome and you get a sudden release of all the
stored energy just to start a new cycle of building up
stress ? Something like an earthquake ?
Just my $0.02...
cheers,
Patrick.
--
---
Patrick Van Esch
http://www.iihe.ac.be/hep/pp/vanesch
mail: van...@dice2.desy.de
for PGP public key: finger van...@dice2.desy.de
Sander Lam
My guess is that the wobbling occurs when both pot and element have a flat
surface, and a little bit of water is locked in between them. Because it's
such a thin layer, and it's so close to the heating source, the water
starts boiling very rapidly. Tiny bubbles of steam search their way out and
cause the wobbling. By the time the pot is hot al the water has evaporated
and the wobbling stops. You should be able to turn the wobbling on or off
by wetting or drying the surfaces.
Best wishes,
Sander Lam
========
Sander Lam
sand...@knoware.nl
This message printed on 100% recycled electrons.
Oz
Obsevation:
Two types:
1) A cracking sound with only a little (fast) vibration. My guess is
that the water (thin layer) immediately over the heat source gets
>100C but immediately above it the water is <100C (<80 ish perhaps). A
lens shape bubble of steam suddenly nucleates and this expands into the
colder water and immediately collapses. If you look carefully you can
sometimes just see them. Similar to the chemists 'bumping'.
2) A pronounced wobble of a kettle (usually finely balanced). This
produces substantial wobbling which can be minimised by re-positioning
the kettle. Often when it is not far from boiling. My guess is that the
bubbles of steam (which do not reach the surface) make the kettle
lighter on one side enough to move the CofG over. This moves the kettle
away from the heat source on that side and/or the bubble collapses. If
the rocking is in (rough) resonance with the bubble creation speed ....
Of course the tap on the bottom when the kettle strikes back home could
be enough to nucleate the next bubble, which would give you a strange,
steam powered oscillator.
Probably total rubbish, but thats my 2P worth.
--
-------------------------------
'Bye, Oz
"Is this all there is to life? No No NO!"
enzoal...@gmail.com
> I was just cooking dinner and noticed the pot rocking on the element.
> It was probably wobbling at about 5-10Hz. I remember seeing this
> before and wondering why it did it. The water was well below boiling
> temperature and their were no bubbles forming on the surface of the
> pan. The vibrations seemed to happen while the pot was heating up, and
> settled down once the pot got hot. Weird!
>
> Any guesses?
>
> <James....@anu.edu.au>
In lamen turms the particles inside the pot are getting soo hot and vibrating soo much the pot is moving from the kenetic energy build up
benj
explanation! Because the spelling is so bad this guy can't even be a
journalist doing journo-science.
First let me say that it's good to be observant and curious. That is the
essence of science. But getting your science explanations from PBS,
journalists, Wikipedia or Usenet losers is the exact opposite from science.
First off a pan wobble is no surprise since that just means the
pan-burner are not quite flat and a teeter-totter or "balance" is set up.
However just normal sloshing of water while common is usually a much
lower frequency because of the mass of the water moving. The higher
frequency implies something else additional going on. And because you
observed no bubbles or boiling creating displacement of the water, there
must be something else going on. And that something else is
"convection". A burner often produces a considerable amount of heat
rapidly heating the water and that heated water tends to rise and
circulate in the pan even when there are no bubbles or boiling yet. This
motion actually creates optical effects where this convection can be
seen by closely observing water being heated.
So yes there is kinetic energy in the water, but a particle description
is in no way needed or useful.
Ned Latham
on the heat.
benj
not specify the type of burner) I have heard pans making a loud "tone"
as the steam escapes from under the pan. Now that note I observed was
higher frequency than 5-10Hz, but amount of water and other parameters
could lower the frequency.
Sergio
which are simply outgassing lead oxide.