system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do hot objects produce infrared radiation?
gpt
The energy we call heat is expressed through the movement of the atoms.  It's not something the atoms have, the energy they possess is the movement itself.  When you feel something hot, you're literally feeling the atoms of that material moving very quickly, and when they touch your slow moving atoms, they basically beat them up.

Why do hot objects produce infrared radiation?  Obviously you don't need to touch a hot object to know that it is hot, you can put your hand near it and feel.  When you put your hand against something hot, you put a lot of atoms in contact with each other.  Remember that the air is also full of atoms, just not as many.  The air is getting beat up by the energy in the hot object, so when you feel near it, you're feeling the air that is excited, which in turn pushes against you.

How is the heat emitted over a distance (radiated)?  First, know that all waves will heat an object when they strike it.  The wave/photon hits an atom and causes it to move, thus we get heat.  An object radiates energy due to the interactions within the nucleus.  If an electron is excited, or jumps an orbital level, the atom carries a bit of extra energy, which is the energy that was used to originally excite it.  This state can only be maintained for so long, eventually the electron goes back to it's normal state and the energy which previously excited it is emitted from the electron.

When you see something that is hot, you will notice that it begins to change color.  As you continue to heat it you will see the colors move from red to blue.  A blue flame is hotter than a red flame.  We can tell this because the wavelength which corresponds to blue has more energy than the wavelength for red, because it's wavelength is smaller.

As we've established, a hot object will radiate electromagnetic waves which fall in the range of visible light.  This is the same process, electrons get energy, hold it for a bit, then spit it back out.  The amount of energy that particular atom received relates to the wave it produces.  Infrared and the visible spectrum are right next to each other, so the hot object is radiating electromagnetic energy across a wide spectrum.  It just so happens that a part of that spectrum we use to see, and another we only sense as heat, or the transformation of kinetic energy to electromagnetic energy.

If you're curious, you can heat an object as much as you want and it won't begin to emit ultraviolet light.  The solution for this problem marked the beginning of quantum physics.