Heat transfer in solids, liquids and gases. Conduction. Convection
There are three kinds of heat transfer: conduction, convection and radiation. In conduction heat passes from the hot part of a body to the cold part through collisions of particles, with no movement of the substance. It occurs mainly in solids: the handle of a spoon in hot tea warms up. Metals conduct heat well (roughly, in W/(m·K): silver 418, copper 395, aluminium 209, iron 73), water (0.6) and wood (about 0.2) poorly, glass wool (0.04) and air (0.026) very poorly. Because they hold layers of air, fur, wool, snow and double-glazed windows keep heat well. Convection is the transfer of heat in liquids and gases by warm (less dense) layers rising and cold (denser) layers sinking. That is why heating radiators are placed low in a room and a cooling unit high; winds and sea breezes are also a result of convection. In a vacuum neither conduction nor convection can occur.
Experiment: place equal-length iron, wooden and plastic sticks in a glass of warm (not boiling) water and feel which warms fastest. Convection: with an adult watch a paper spiral turn above a warm radiator. Safety: do not experiment with boiling water, open flame, a gas hob or hot metal.