If heat is the measure of atomic kinetic energy and cold is technically the lack of heat then how can we feel radiated cold? Like if you put your hand near some ice you can feel the cold? How can the lack of something radiate?
In: Physics
A couple of ways:
For starters, you’re always radiating heat due to “black body” radiation (the hotter something is, the more it radiates). So is everything else around you that has a temperature. But if the things around you are colder than you, you’ll probably radiate more to them then they’ll radiate back, making you colder over time. But this effect is pretty small in a lot of cases and can sometimes be ignored.
Another way is through conduction: the air around you, even while completely still, still exchanges heat with you. It also allows some heat to trickle through it. Again, you’re trading more heat to it than it’s trading back, so you feel cold.
Finally, there’s “free” convection: this is where the air, which changes density based on temperature, can tend to move around on its own to move heat even faster through it “mixing” hot air with cold. This can be slower than would be noticeable or pretty extreme depending on the context, but either way, this can transfer heat from something like a cold window to the air around it relatively rapidly. Barriers like curtains can actually slow this down quite dramatically by trapping air between a window and the rest of a space, slowing the rate that heat escapes, which is why they’ve historically been quite popular. Alternately, If your hand is very close to ice, there’s a pretty massive temperature gradient in the air between your hand and the thing, which can accelerate this effect dramatically, and transfer the heat in your hand to the ice very quickly which feels like “radiating cold”
Latest Answers