What do we feel when we say something is "hot"?

examorph

So recently I had learnt that temperature is just the average kinetic energy in the system, the more KE in the system particles the higher the temperature, KE is mv^2/2 meaning that temperature is just really the average of how much the particles in the system are vibrating, now this makes me wonder, what exactly do we feel when we say something is hot, is it just the vibrations of the particles that we feel and when these vibrations get larger we say something is geting hotter?

russ_watters

Yes.

haruspex

Yes, but...

The temperature relates to the average energy per state, rather than the average energy per particle. A monatomic gas only has three states for holding energy, its movements in the three dimensions. A diatomic gas has those three plus two rotational states, so each particle can hold more total energy at the same temperature.

How hot something feels to the hand also has a lot to do with conductivity. If you touch a metal bar at 50C that will feel pretty hot; touching a block of wood at 60C will be a lot more comfortable. This is because you only have to absorb a small amount of heat from the surface of the wood for that surface to become a lot cooler. The conductivity of the metal keeps replenishing the surface heat from deeper in the bar as fast as your hand can conduct it away.

D H

Yes and no.

You have two kinds of thermoreceptors in your skin. One set responds to warm temperatures, those above 77°F or so. These warmth sensors are quiet for temperatures below this threshold. Another set responds to cooler temperatures, those below 70°F or so. Both kinds of thermoreceptors saturate. The warmth sensors don't detect burning hot as any warmer that just plain hot. They saturate well below temperatures that do damage.

The heat you detect as painfully hot results from a dual firing of your warmth thermoreceptors firing at max and a different set of somatic sensors. Extremely high temperatures cause cell damage. These damaged cells leak chemicals, and this leakage does (at least) two things. It kicks your immune system into overdrive so as to repair the damage, and it triggers a sensory response in yet a different kind of somatic sensors, the nociceptors (colloquially, pain sensors).