My question is the following: Why does it feel colder (i.e. why does your body transfer more heat to the surroundings) when you are moving through the air at a high velocity, f.ex. when you are driving a motorcycle? Logically, temperature is a measure of the average kinetic energy of air. When you drive faster, the air is moving at a higher velocity relative to you, so the average kinetic energy with respect to your moving frame of reference should increase as well. Why wouldn't the air "feel" hotter in this scenario, and why does the opposite happen?
Thermodynamics – Why Cold Air Feels Colder When Moving Through It Quickly
thermodynamics
Related Solutions
Short answer:
The thermometer measures actual temperature (which is the same for both), while your hand measures the transfer of energy (heat), which is higher for the pot than the air.
Long answer:
Keyword: Thermal Conductivity
The difference is a material-specific parameter called thermal conductivity. If you are in contact with some material (gas, liquid, solid), heat, which is a form of energy, will flow from the medium with higher temperature to the one with low temperature. The rate at which this happens is determined by a parameter called thermal conductivity. Metals are typically good heat conductors, which is why metal appears colder than air, even though the temperature is the same.
Regarding your second question: the thermometer will show the same temperature. The only difference is the time at which thermal equilibrium is achieved, i.e. when the thermometer shows the correct temperature.
Final remark: the rate at which heat (energy) is drained from your body determines whether you perceive a material as cold or not, even if the temperature is the same.
For reference, here is a table which lists thermal conductivities for several materials:
In a Fermi-Dirac distribution, the relationship between temperature and the speed of particles is not intuitive. Even at cold temperatures, fermions can have high speeds simply because of degeneracy - the lower momentum states "fill up", leaving only states with large momentum available, and this is true even at very cold temperatures. However, the heat capacity of the conduction electrons is negligible - heat cannot be extracted precisely because there are no lower energy states available.
The reason that metals feel cold is because they have a high thermal conductivity. This can also be attributed to degeneracy of the conduction electrons, since in a degenerate electron gas there are few available lower momentum slots into which a conduction electron can be scattered. This means that the electrons have a relatively long mean free path between scattering events and are able to transfer heat efficiently from your finger into the metal and then away. Thus the temperature of the metal where you touch it does not rise to match your skin temperature.
I don't think phonons come into this at all. In metals, electron heat conduction dominates phonon transport.
Best Answer
I wrote an answer to a related question on the Gardening site. I will re-use some of the words from that answer here:
First important thing: heat moves from warm to cold; and the greater the temperature difference, the faster heat moves.
Wind chill is used to describe "feels like" temperatures - recognizing that when a wind blows, the air "feels" colder. Here is what is actually going on:
Objects lose heat through a number of mechanisms:
In all these cases, heat moves from a hotter body to a colder body. Now when a body generates heat (like humans and other mammals), the rate at which you generate and lose heat must balance. We can sweat when we are hot (increase evaporation) or shiver when we are cold (increase heat production). How efficient these mechanisms are depends on several things. Convection and evaporation depend strongly on air flow.
When there is no wind, you will (slightly) warm up the air around you which then acts as a "blanket". Wind keeps replacing the warm air with cooler air, meaning you lose heat more quickly (because heat loss is proportional to the temperature difference). Wind chill is used to describe how this "heat stripping" affects warm bodies more strongly when the wind is stronger. It's not that an object will cool below ambient temperature due to the wind - just that it will lose heat more quickly. This is important for mammals who try to stay warm: if you lose heat faster than you can make it, you will eventually succumb to hypothermia.
Engineers use something called the h factor to describe this phenomenon. When you have a surface at temperature $T_1$ in contact with a fluid (which could be air) at temperature $T_2$, the rate of heat exchange across the interface is given by
$$q = h_c A (T_2-T_1)$$
The coefficient $h$ for air is a function of air speed, as given by this graph:
Image from Engineering toolbox article on Convective Heat Transfer
The curve at very low air speeds depends on many factors like surface texture - but the trend clearly shows that "faster air flow leads to faster heat transfer".
For evaporation, the situation is a bit more complex still. Evaporating water actually "draws heat" from the surface. This is because not all molecules move at the same speed - and it's the fastest molecules that have the best chance of escaping. When the smartest person leaves the room, the average IQ in the room goes down a bit; when the hottest molecule in the liquid leaves, the rest of the liquid becomes a little bit colder.
This effect is more significant when the relative humidity in the air is low, because once relative humidity reaches 100%, moving the air around doesn't expose the surface to "drier" air. However, since the saturated vapor pressure of water drops very quickly with temperature, the rate of evaporation (and therefore the rate of heat loss due to evaporation) is much less when temperature is lower.
In summary: warm bodies (significantly warmer than the environment) will lose heat more quickly when there is a wind blowing. A cold (unheated) body will NOT, however, cool down all the way to the "wind chill temperature".