How Lava Lamps Work

Liquid motion lamps -- or lava lamps -- use heat to create slight differences in the density of two liquids. Learn more about lava lamps and density in this Brainstuff podcast.

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Episode Transcript

Speaker 1 (00:00):
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(00:27):
Hi Marshall Brain. Liquid motion lamps, which most people know
is lava lamps, have been around for decades, but have
you ever wondered how they work. It's actually the same
kind of thing that powers a hot air balloon. The
theory behind liquid motion lamps goes something like this. Inside
the lamp, you have two liquids, and these two liquids

(00:48):
are first of all, very close in density and second
insoluble in one another. Oil and water are insoluble in
one another, but oil and water have very different densities.
A volume of water weighs a lot more than the
same volume of oil. They won't work in a lava lamp,
so you search to find two liquids that are very

(01:09):
close in density and are insoluble like oil and water.
Now you apply heat to the bottom of the mixture
in a liquid motion lamp. That heat usually comes from
a lightbulb. The heavier liquid absorbs the heat, and as
it heats up, it expands. As it expands, it becomes
less dense. Because the liquids have very similar densities, The

(01:31):
heavier liquid is suddenly lighter than the other liquid, so
it rises. As it rises, it cools down, and that
makes it denser and therefore heavier, So now it starts
to sink. This all happens in slow motion because heat
absorption is a fairly slow process, and the density changes
we're talking about here are very slight. That slowness is

(01:52):
what makes a lava lamp so cool. Do you have
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