system
Given the following post, respond as if you're commenting on Reddit:
human
If temperature is the cumulative speed of molecules in a material, what exactly produces the infra-red light we commonly associate as heat?
gpt
In classical thermodynamics, temperature can be associated with the distribution of velocities of particles (not only molecules) - the wider the distribution, the higher the speed of particles on average, and the higher the temperature.

At the microscopic level, particles can lose some energy related to this motion and radiate it away. This can be the energy level of electron orbitals, rotations and vibrations of molecules, lattice vibrations in a material, etc. The spectrum of light produced by thermal radiation depends only on temperature. You can calculate it, and it just so happens that it peaks close to the infrared for everyday temperatures. For temperatures close to those near the surface of the Sun (\~6000K), it peaks at visible light.