By radiation, heat propagates without leading to a movement of matter, only the mechanical energy waves or electromagnetic energy waves move. Heat radiation propagates through gases, often by air. Through convection, takes place a movement of substance, fluids, liquids or gas from bottom up and vice-versa. Hot particles become lighter and rise, their place being taken immediately by the cold particles. The hot particles now are far from the heating source, they release the heat and become cold and heavy again, going down to the heating source level. In this way the cycle continues.