1. Hi,

There is a physical paradox that has been told and retold enough times to almost be an urban legend.

When you boil water in a metal pan with a metal handle, the handle gets warm, but, with luck, you might still be able to hold it as you take your pan off the fire. The moment you pour the water out, the handle becomes so much hotter you drop it with a gasp.

The explanation that's been making the rounds is that the water was taking heat away from the metal, so when the water is gone, the metal becomes hotter because nothing is taking the heat away anymore.

I find this explanation illogical - you could just as well put the plug back in the drain of your bath and expect the half-emptied tub to magically top up again (without any fresh water coming from the faucet), "because nothing is taking the water away anymore". Or hope to get your money back as soon as you have stopped drinking.

I think I once met a more plausible explanation, and it involved some particular properties of aluminium, from the solid-state physics department. It also said the paradoxical behaviour can only be found in aluminium pans, not steel or copper ones. But I cannot remember the details.

Any clues, opinions, remarks?

Looking forward,
L.

2.

3. There are a lot of urban legends. I never heard that one, nor felt a pan get hot after pouring out the water. The first thing I would ask is whether it actually does happen.

4. A psychological thing perhaps. Your mind would rather drop an empty pan than a pan full of hot water so temporarily blocks the pain of the heat out.

5. Is there a possibility that what causes the pain is actually a type of "ice burn" if you like, but at hotter temperatures........that is to say a rapid cooling of the handle.....you pour the hot water out, in rushes cool air, thermodynamics does the rest?

6. I haven't heard this one either, and have not experienced it. The residual heat in the pan, which is hotter than the handle, the water and the air, has to go somewhere. I'd say it's possible, depending on the size, material and thickness of the pan.

7. It seems plausible if you assume that the bottom of the pan (that was in contact with the burner) is a lot hotter than the handle. Once that heat starts to distribute throughout the pan and there isn't any water to act as a heat sink, the handle might get hotter.

That being said, it seems very unlikely to me that a pan could actually have that big of a temperature gradient...

8. Originally Posted by Leszek Luchowski
Hi,

There is a physical paradox that has been told and retold enough times to almost be an urban legend.

When you boil water in a metal pan with a metal handle, the handle gets warm, but, with luck, you might still be able to hold it as you take your pan off the fire. The moment you pour the water out, the handle becomes so much hotter you drop it with a gasp.

The explanation that's been making the rounds is that the water was taking heat away from the metal, so when the water is gone, the metal becomes hotter because nothing is taking the heat away anymore.

I find this explanation illogical - you could just as well put the plug back in the drain of your bath and expect the half-emptied tub to magically top up again (without any fresh water coming from the faucet), "because nothing is taking the water away anymore". Or hope to get your money back as soon as you have stopped drinking.

I think I once met a more plausible explanation, and it involved some particular properties of aluminium, from the solid-state physics department. It also said the paradoxical behaviour can only be found in aluminium pans, not steel or copper ones. But I cannot remember the details.

Any clues, opinions, remarks?

Looking forward,
L.
I don't believe this one, unless there are some additional conditions -- see below. (Edit -- the scenario below is essentially that suggested by Scifor Refugee)

You might be able to get something like that to happen if you were heating the pot extremely rapidly so that there was a huge temperature gradient between the bottom of the pot and the handle, with the water relatively cool (relative to the bottom of the pan and the source).

In that situation the heat in the bottom of the pot would tend to flow towards the low temperature/high heat capacity sink formed by the water and the sides of the pot would remain fairly cool. If you then dump out the water the heat would equilibrate in the metal of the pan, heating the sides and the handle.

This would be strictly a transient effect, and fairly difficult to reproduce. To do it you would need a very high temperature heat source to create the large temperature gradient in the pan.

To do this I would think that a thick bottom and thin sides on the pan would accentuate the effect. You would also need good thermal contact between the handle and the pan.

9. Your doubts sould be inmediately solved using a thermographic camera ;-D

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