Convection. Animation of molecules in a gas or liquid undergoing convection. An energy source (coil at centre) is heating the molecules at centre, causing them to rise (orange). At the rising plume reaches the top of the container, the molecules move outwards to either side. They then cool and fall downwards (blue). Molecules either side of the energy source move inwards to replace the rising column of hot gas or liquid. This cyclic process results in circulating streams of molecules known as convection currents.