Here's why:

* Conduction: Heat is transferred through direct contact between particles. The hotter particles vibrate more rapidly, and this vibration is passed along to the cooler particles, transferring energy. No bulk movement of the material itself is involved.

Let's compare it to other heat transfer methods:

* Convection: Heat is transferred through the movement of fluids (liquids or gases). Warm fluids rise, and cooler fluids sink, creating currents that carry heat with them.

* Radiation: Heat is transferred through electromagnetic waves, which can travel through a vacuum. The sun warming the Earth is an example of radiation.

So, conduction is the only process where heat transfer occurs without the movement of the material itself.