system
Given the following post, respond as if you're commenting on Reddit:
human
Why does 100°C water feel so much hotter, more painful, and cause more damage than 177°C air?

For example, submerging your hand in boiling water will cause severe burns, but you can easily put your hand inside a hot oven for much longer than you could in the boiling water. 

Also, why does a soft rug at 0°C feel warmer to your bare feet than a concrete floor at the same temperature?
gpt
This is a common question.  There are two reasons water feels hotter (or colder) at the same temperature than air:

1) Thermal conductivity.  Water has a thermal conductivity about 25 times that of air.  That means that, given the same temperature difference between water and something else (for example, your skin) compared to air, the water will transfer about 25 times as much heat per second.

2) Heat capacity/thermal mass.  Water is also much more massive than air per unit volume - it's a little over 800 times as dense. Heat is stored in mass, so water being 800 times as dense as air means that it can hold about 800 times as much heat just on that basis.  In addition to the amount of mass, water also has a higher heat capacity (how much heat it takes to raise a specified amount of mass a specified number of degrees) than air - about 4 times as much. So because there's 800 times as much mass per unit volume, and that mass can hold 4 times as much heat per degree, water can hold over 3200 times as much heat per unit volume as air does. 

In combination, (1) means water can heat you up a lot faster than air, and (2) means there is a *lot* of heat to dump into you - the water cools down a lot more slowly than air would.


A rug feels warmer than concrete basically for the same reasons - it's less thermally conductive than concrete and it has less thermal mass.  So you don't lose nearly as much heat when you're touching a rug as you would when touching concrete.