Why is it that if we wet our fingers before putting out a candle, we don’t get burned, but if we grab a hot pan out of the oven with a wet oven mitt, we get burned?

Question

Why is it that if we wet our fingers before putting out a candle, we don’t get burned, but if we grab a hot pan out of the oven with a wet oven mitt, we get burned?

In: Physics

Answer 1

The water isn’t especially important in this question, it’s only acting as a heat battery. The water absorbs some heat, but too much and it evaporates. The important thing here is how you frame the sources of heat in your heat. When you dip your finger in wax, you remove a portion of wax from the candle, and with it comes an equal portion of the heat energy in the ENTIRE CANDLE(this is important).

Think of it like this. You have a burning candle with a pool of wax in the center. You dip your finger into the wax, and when you pull it out, let’s say 1% of the wax came with it. Now, for a moment, that 1% of wax also holds 1% of the heat stored collectively in the rest of that wax pool. So you’re getting 1% of the heat of the entire candle. The layer of water can pretty easily absorb most of that heat, bringing it down to safe temperatures before it reaches your nerves.

Now lets move on to the pan. So you have a wet oven mitt, and a VERY hot pan. Much larger layer of water, but not that much hotter heat source. What’s the difference? Well first off, the metal pan can store a lot more heat than the wax, but that’s not the really important bit. When you touch the metal pan, you’re not removing 1% of the pan and taking that heat. You’re taking the heat of the ENTIRE pan. No 1% stuff here. This is equivalent to dipping your entire hand into a pool of 400 degree candle wax AND LEAVING IT.

In one case, the heat source is liquid, and when you dip into it and pull out, you’re only dealing with a portion of the total heat in the system.

In the second case the heat source is solid, and you are forced to deal with the entirety of the heat stored in the heat source.

In both cases, the water serves as both a store of energy and a conductor of energy. In the first, the energy is sufficiently low that the water can take it. In the second, there is too much energy, and the water is thermally massive enough to take it without evaporating, but also not massive enough to avoid heating up to scalding temperatures.