is the passing of kinetic energy through the collision of particles or ions. This happens best when particles are close together as they are in solids. Or when there are free electrons that can diffuse through the material, as in metals.
is the mass movement of particles with kinetic energy. This requires the particles to be able to move past each other as they can in a fluid. The currents are normally due to warm, less dense fluid rising. A fan oven uses forced to equalise the temperature throughout it. Stirring is another example of forced .
is electromagnetic waves that do not require a medium to travel through. Dark objects are the best emitters and absorbers of infra-red .
