Eli5- Why does water feel so much colder than air?

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When I’m at the beach and the water is around 23-25°C, it feels like touching ice but when air temperature ist around there, sometimes even topless it’s hot, even in the shadow. Or even if it’s cool, it doesn’t feel that cold

In: 6

Density. Water has a lot more molecules in contact with your skin to carry away heat. Air has very few. As a result, the heat transfer is much slower in air than water.

This is why you can reach into an oven at 212/100 degrees and think it’s just very warm while putting your hand in boiling water would be, well, putting your hand in boiling water.

Heat is transferred much more efficiently in water that air. I think something close to 40 times more efficiently.

I think it has something to do with heat transfer. Whether something feels cold or warm depends on how well it transfers heat. So air is pretty good at transferring heat. A cup of coffee will quickly get cold if you put i outside, as the air is much cooler that the coffee, and so will take the heat away.

Water is even better at taking heat away than air, so if you go into the water, it will suck out your body heat even faster than the air, even if it is the same temperature as the air. That is what feels cold. This also the reason why e.g., iron feels colder than wood, because it transfers heat much better.

Fun fact: Evaporation transfers heat even better than water. That is why it can feel even colder when you leave the water and are wet, than it felt down in the water, because the water evaporates from your body.

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Feel free to correct me if i am wrong, im a philosopher, not a phycisist 🙂

As others have stated, it’s about the rate of heat transfer. To understand how that impacts our comfort, understand that our bodies are constantly rejecting heat. We produce heat through various metabolic processes as well as through physical movement.

Our internal temperature is around 37C. We are most comfortable in still air around 25C because that 17C difference happens to be enough to keep the rate of heat transfer via conduction through our bodies to our skin (which is somewhere between 37C and 25C) and via convection from our skin to the cooler air, about equal to the rate that we produce heat.

Since water is a better conductor of heat, 25C water removes more heat than still 25C air, so we perceive it as being “colder.”

Similarly, moving air will remove more heat than still air at the same temperature, due to forced convection. As a result we feel “colder” on a windy 25C day than a still one.

Generally speaking we don’t sense temperature, we sense the rate of heat transfer.