Why can I touch hot things longer with water on hands?

Question

So I have done a couple of personal experiments with water on my hands. One day I was taking bread (rolls to be exact) out of the oven with my bare hands and burned my hands when my hands were dry. Then a couple days later my hands were wet and took them out and did not feel pain and did not feel like I had to let go of the rolls for about 3 to 4 seconds.

Another "Experiment" that I had was I had was I wet my hand with saliva and put it above the flame of a candle and I lasted about 3.6 seconds and my friend lasted less than a second. My question is why can I touch things longer when my hand are wet?

Answer 1

There are three things that can come int play when water is involved. Which one is the main contributing depends on temperature and contact pressure.

1. The water film needs to heat up, look up heat capacity of water, first. I.e. the heat must travel through the film first.
2. The water evaporates slowly, therefore cooling the finger/hand
3. If a complete vapor layer is created the reduced heat conductivity of gas protects the hand. Look here

Answer 2

The Leidenfrost effect may be at work:

The Leidenfrost effect is a physical phenomenon in which a liquid, in near contact with a mass significantly hotter than the liquid's boiling point, produces an insulating vapor layer keeping that liquid from boiling rapidly. Due to this 'repulsive force', a droplet hovers over the surface rather than making physical contact with it. This is most commonly seen when cooking: one sprinkles drops of water in a pan to gauge its temperature: if the pan's temperature is at or above the Leidenfrost point, the water skitters across the pan and takes longer to evaporate than in a pan below the temperature of the Leidenfrost point (but still above boiling temperature).

It will depend on on how wet the hand is, how absorbent the cookies and such.

Answer 3

Like all experiments, yours needs to have interfering variables accounted for and under control. For example, how did you wet your hands, and what was the temperature of the water? If you ran water from a faucet over your hands, the main factor would be that you cooled the skin of your fingers. Your fingers would take thermal energy from the surface of the rolls without reaching an uncomfortable temperature for your fingers. The roll material would be a poor conductor of heat (but that's another variable), so the thermal energy deeper in the roll wouldn't get to your skin very quickly.

The wet finger above the flame would be different. If you licked your finger, you didn't cool it down. The temperature at the level where you held your finger is an important variable we don't know. I would guess that the temperature was much greater than the temperature of the rolls. The protection of your finger most likely came from vaporizing the water. Vaporizing an amount of water takes much more thermal energy than just heating it up.

Answer 4

The specific heat capacity of water is high. With a watery layer (wet) hand, the water will absorb the heat from the hot object but the temperature of the water will rise just a little (Q=mc delta T) Therefore, your hand is in fact contacting the cooler water but not the hot object.