The kinetic theory of matter states that all phases of matter have free-moving particles. Heat is transferred when high-energy, free-moving particles collide with slower particles. A chain reaction of collisions causes heat to transfer from one part of the solid to the other.
The temperature of an object is based on the kinetic energy of the particles inside it. When an object is heated, the free-moving particles near the heat source are excited and create heat in object. These excited particles move faster and eventually collide with slower particles. The slower particles become excited and absorb energy from the other particle, which transfers heat. As the excited particles continue to collide with the slower particles, the heat created is transferred to each slower particle, moving across the surface of the object.
Heat transfer in gases is weak because of the distance between particles. Solids have less distance between the particles, but the structure of the solid constricts the movement, which is why wood does not have good heat transfer. The process of heat transfer from higher temperature or higher energy particles to cooler temperature or lower energy particles is called conduction. Heat transfers caused by radiation and convection are governed differently.