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Author Topic: What makes a heated metal pan vibrate?  (Read 3891 times)

Offline cheryl j

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What makes a heated metal pan vibrate?
« on: 14/04/2013 03:38:59 »
I've noticed occasionally that if I put a metal pan on the stove and it gets very hot, it will vibrate or shake. I know metal expands, and that heat increases the kinetic energy of molecules. But do the molecules actually start moving back forth in the same direction in a way that actually causes the whole object to shake or is it uneven expansion that causes it?


 

Offline Ethos_

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Re: What makes a heated metal pan vibrate?
« Reply #1 on: 14/04/2013 05:01:33 »
I've noticed occasionally that if I put a metal pan on the stove and it gets very hot, it will vibrate or shake. I know metal expands, and that heat increases the kinetic energy of molecules. But do the molecules actually start moving back forth in the same direction in a way that actually causes the whole object to shake or is it uneven expansion that causes it?
I've seen this occur when the pan had a little moisture let on it's undersurface. This is caused by the moisture turning to steam between the pan and the burner surface. Not sure if this is the same cause in your case but it has happened to me before.
 

Offline damocles

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Re: What makes a heated metal pan vibrate?
« Reply #2 on: 14/04/2013 05:19:17 »
I have also noticed this, it is certainly a legitimate phenomenon.
Metal atoms in the pan material moving backwards and forwards in synch. is the least likely explanation.
Uneven expansion of an irregular metal surface is a possible explanation, and perhaps the simplest.

Any solid surface will have 3 points of contact with another. If there are two points of contact that are almost on a balance line of the pan, and a third and a fourth potential point of contact on opposite sides of the balance line, it may be possible for heating to make the third point of contact in a less dense region of the pan, which will then cause it to tip to the fourth. The fourth point of contact will then be heated, while the third point, no longer in contact with the metal will cool, and the balance will be reversed, and so on.

For any real solid though, there will be an ad-layer which will partially desorb as the result of the heating. This will lead to an expanding gas sample which will break the one contact in favour of the other. As the gases cool they will be re-adsorbed, and the original points of contact re-established.

I think either of these last two might be the explanation, but I really do not know.
 

Offline syhprum

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Re: What makes a heated metal pan vibrate?
« Reply #3 on: 14/04/2013 07:02:02 »
I am sure that moisture is the explanation if you lift the pan, wipe its underside dry and wait while the moisture boils of the hot plate that will cure the problem.
 

Offline chris

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Re: What makes a heated metal pan vibrate?
« Reply #4 on: 14/04/2013 10:56:02 »
I've seen this happen with dry pans; I think it's differential expansion of the metal surface causing the pan to wobble; this, in turn, further exaggerates the differential expansion because the wobble causes different parts of the pan to be heated at different rates; the result is resonance, until the pan surface becomes uniformly hot.
 

Offline lightarrow

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Re: What makes a heated metal pan vibrate?
« Reply #5 on: 14/04/2013 11:57:11 »
Many years ago I read somwhere of a sound effect (it probably had even a precise name) generated by cold metal bodies resting on hot surfaces; I remember the case of a lead bar resting on the surface with two points or two segments: one of the two, casually, heats more than the other expanding it and giving the bar a momentum which lift it that side; then that side cools and goes down while the other is pushed up, and so on, many times per second, generating a distinct sound.
Someone remember the name of this effect?
« Last Edit: 14/04/2013 12:00:16 by lightarrow »
 

Offline JP

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Re: What makes a heated metal pan vibrate?
« Reply #6 on: 14/04/2013 14:08:20 »
Many years ago I read somwhere of a sound effect (it probably had even a precise name) generated by cold metal bodies resting on hot surfaces; I remember the case of a lead bar resting on the surface with two points or two segments: one of the two, casually, heats more than the other expanding it and giving the bar a momentum which lift it that side; then that side cools and goes down while the other is pushed up, and so on, many times per second, generating a distinct sound.
Someone remember the name of this effect?

Good point, lightarrow.  Growing up, my parents had an electric stovetop and I was accustomed to this sound when turning on a burner under a cold pot.  Nowadays, I have a gas stove, so I don't get this sound anymore.  I'm curious if the OP or others who have heard this are using gas or electric?
 

Offline cheryl j

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Re: What makes a heated metal pan vibrate?
« Reply #7 on: 15/04/2013 02:45:55 »


... The fourth point of contact will then be heated, while the third point, no longer in contact with the metal will cool, and the balance will be reversed, and so on...



I like that explantion the best. It makes sense to me. And yest it's on an electric stove with the flat coils.
« Last Edit: 15/04/2013 02:54:54 by cheryl j »
 

Offline evan_au

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Re: What makes a heated metal pan vibrate?
« Reply #8 on: 15/04/2013 16:23:39 »
Perhaps it is slip/stick friction between the pan and the electric element as they heat up?
Since they are made of different materials, they are likely to expand at different rates. Tension will build up for a short time until it overcomes the friction between the surfaces, and it jumps a little, releasing the tension.
Then it heats up a bit more then jumps a bit more, cyclically, until they both reach a stable temperature. This jumping will produce a noise or a vibration.

You could experiment see if it is caused by moisture by trying it with a completely dry pan.
 

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Re: What makes a heated metal pan vibrate?
« Reply #8 on: 15/04/2013 16:23:39 »

 

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