Lava lamps, also called liquid motion lamps, have been around for decades. The theory behind a liquid motion lamp is that you need to have two liquids which are very close in density and also insoluble in one another. Oil and water are insoluble in one another but oil and water have very different densities so they won't workNext, you apply heat to the bottom of the mixture. In a lava lamp, the heat usually comes from a light bulb. Heating a compound activates the molecules so that they spread apart, making the compound less dense. Cooling the compound down again increases the density. The heavier liquid absorbs the heat, and as it heats up, it expands. As it expands it becomes less dense (the density changes here are very slight, however). Because the liquids have very similar densities, the formerly heavier liquid is suddenly lighter than the other liquid, so it rises. As it rises, it cools, making it less dense and therefore heavier, so it sinks. This represents the principle of heat convection.  Schematic of a lava lamp Sources:1) www.howstuffworks.com2) www.primenet.com3) nene.essortment.com...
