How does thermal energy travel through a solid?

Thermal conduction is energy transfer through matter that stays in place on a large scale. A solid rod can transfer energy from a hotter region to a colder one without the whole solid flowing from one end to the other. A temperature difference drives the net transfer.

Particles in a solid still have microscopic motion. They interact with neighboring particles and can pass energy onward while remaining near their structural positions. This makes the movement of energy different from a stream of solid material. In metals, mobile electrons can contribute to energy transport as well.

The initial illustration holds the left end at 60°C and the right at 20°C. Its energy arrow points rightward, toward the colder end. Reversing those maintained temperatures reverses the net direction. With equal temperatures in the ideal steady comparison, there is no preferred net transfer, although microscopic motion continues.

Conduction is different from convection, in which a fluid moves in bulk and carries energy with it. The rod picture supplies direction but not an exact rate. Material, cross-sectional area, length and contact conditions would matter for a quantitative calculation. The drawn particles and arrow are a teaching representation, not a measured microscopic movie.