Ask a Physicist Answers
A friend of mine claims to notice that when he takes a hot frying pan (with a warm, insulating handle), and pours cold water into it, the handle seems to get hotter. He thinks it is because the handle is less insulating than the air, thus the path of least resistance is through the handle.
This would make sense to me when you take the pan off of the heat, but he claims that it isn't until the water hits it that the handle gets significantly hotter. If this is true, what does the water have to do with it? If anything, wouldn't the water become the path of least resistance, and heat would move from the metal to the water, and from the handle to the air?
—Question submitted by Zac Moreland from Montreal
Thanks for your question Zac. We had a fairly lengthy discussion about your question here at the office, and three different theories emerged. Consequently, we have three different answers for what might be going on in your friend's kitchen.
Frying Pan Physics
Although the conditions of this experiment are not described precisely, here’s a guess at how pouring cold water into a hot frying pan could heat up the insulated handle:
When the cold water hits the hot frying pan, some of the water will vaporize, i.e. turn into steam. If the conditions are right (for example, if the frying pan is in a relatively confined area with limited air circulation), some of the steam will condense on the handle of the frying pan. Now condensation is the opposite of evaporation.
We all know that when water evaporates from a surface, the surface cools down. Similarly, when steam condenses on a surface, the surface heats up. So the cycle of vaporization and condensation uses water as a means of transferring heat from the frying pan to the handle.
-Answered by Alan Chodos, PhD
I have a different answer. As Alan noted, the conditions are not precisely described and my answer assumes you are using an electric stove. The biggest factor in heating on an electric stove is contact area. The more of the pan that is touching the heat source, the fast the pan and contents will heat up. When water is poured into the pan it makes the pan heavier and so the pan pushes down on the stove with more force and the contact area increases.
Now the whole pan, including the handle, heats up more quickly. If you want to test this hypothesis you can put the pan on the stove and then put something heavy but not liquid, like a chicken breast, in the pan and see what happens to the handle. If I’m right, the handle will still head up. If Alan’s right the handle will stay cool. You could also see what happens when this is tried on a gas stove.
—Answered by Becky Thompson, PhD
One More Possibility
It may be that Zac was on to something with his guess about the thermal conductivity of the pan and the material inside being behind the change in temperature of the handle when his friend added water to a hot pan.
Frying pans are often made of cast iron because iron conducts heat rather poorly. Imagine that an empty pan is placed on a small, but hot burner. The heat must travel through the bottom of the pan and up the side before it reaches the handle.
It’s the long path that keeps the handle relatively cool. Once you fill the pan with something, it will heat up until it’s essentially at the same temperature as the bottom of the pan. Because hot material (boiling water, for instance) is now very close to the handle, the heat doesn’t have to travel as far through poorly-conducting iron to reach the handle.
In order to check this, I did an experiment this morning with a stainless steel pot. Like iron, stainless steel is a poor heat conductor. In order to make sure the difference in temperature (if any) was as dramatic as possible, I chose a very deep pot.
First, I put a small amount of water in the bottom of the pot and brought it to a boil.
Even after several minutes of boiling, the handles felt cool to the touch, I assume because the handles are far from the heat source
Next, I filled the pot until the water was up to the point where the handles are attached. Once again, I brought the pot to a full boil. That meant that boiling water was essentially in contact with the base of the handles.
This time the handles were quite warm. They were still cool enough to touch, but it wasn’t comfortable.
So, Zac, I think your hypothesis was probably very close to the answer, although Becky and Alan’s hypotheses could contribute to the temperature change as well. Without further experiments, it’s hard to say for sure which is the dominant factor.
—Answered by James Riordon, Head of Media Relations at APS