I can hang out buck naked in 70 degree F outside all day but not touching 70 degree F water.
In: Earth Science
The feeling of cold is the result of the environment removing heat energy from your body, not the temperature difference between your body and the environment. In general, the difference in temperature (98.6F and 70F) is the driving force for this heat transfer so we associate the feeling of cold with the temperature difference, but there is another factor involved.
The “film coefficient” between your skin and the environment affects the amount of heat that leaves your body over time, for any given temperature difference. As it has been previously stated, the film coefficient between skin and water is much higher than skin and air, resulting in more heat transferred from your body to the environment.
While it is not quite the same, you can see a similar difference in the heat transfer coefficient numbers for a heat exchanger (an industrial device). These numbers are for the overall heat transfer coefficient, which includes the film coefficient, but also includes some other factors. Still, they illustrate the difference between air and water.
Air -> Cast Iron -> Air = 1.0
Water -> Cast Iron -> Water = 40 – 50
So for the heat exchanger, wetted surfaces transfer heat at approximately 50 times the rate.
Your skin probably does not have this exact multiple of 50, but it will be a significant difference that increases heat energy transferring out of your body to the environment, resulting in you feeling cold.
[https://www.engineeringtoolbox.com/overall-heat-transfer-coefficients-d_284.html](https://www.engineeringtoolbox.com/overall-heat-transfer-coefficients-d_284.html)
It’s the rate of heat transfer.
Liquids are much denser than gases. Picture liquids as a plastic ball pit, and gases as a mostly empty room with a few pingpong balls being tossed around inside.
**70F air**: You are standing in a room where 2 or 3 people are tossing 70F pingpong balls at you. Your own temp doesn’t change much because there aren’t many impacts.
**70F water**: You are submerged in a ball pit of 70F balls. Hundreds are contacting your skin all the time. You cool off much more quickly.
Also the way you *feel* the temp of things is actually related to the *rate* of heat transfer in/out of you, not the thing’s actual temp! Imagine a wooden toilet seat vs a cold plastic one. Both are the same temp but the wood one transfers your heat away slower, so it feels warmer. Go outside in the winter and compare touching a tree and grabbing a metal railing. Both are the same temp but the metal feels WAY colder, same reason.
It’s because of the efficiency of heat transfer–when thermal energy moves from something warm to something cooler. In this case, from your 98.7 degree (F) body to the 70 degree air or water. Water is a better conductor than air, so when you get into the water heat escapes/is transferred out of your body at a much faster rate, leaving you feeling colder, faster than you would if you were just standing in 70 degree air.
The way you feel the temperature is through the heat going in or out of your skin. Water is much better at pulling heat out of your body then air is, so it feels colder. Also, water will pull more heat out of your body then air will, so it will feel colder still.
You lose heat to water like 25 times faster than you would from air. 70° air is more or less equilibrium, you won’t overheat, underheat, it’s litty.
Up the rate of heat loss 25x with water of the same temp and now you get cold. You lose heat faster than you make it.
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