Why doesn't the oil float on top of the alcohol?
Since oil floats on top of water, you might have thought that oil would
float on top of alcohol, too. But the oil sinks to the bottom and the alcohol
floats on top of the oil. Even though water and alcohol are both clear liquids,
they have different densities. Alcohol floats on top of oil because a drop
of alcohol is lighter than a drop of oil the same size.
Why don't oil and alcohol mix? For that matter, why don't oil and
The answers to these questions have to do with the molecules that make
up oil, water, and alcohol. Molecules are made up of atoms, and atoms are
made up of positively charged protons, negatively charged electrons, and
atoms that make up water molecules and alcohol molecules are arranged so
that there is more positive charge in one part of the molecule and more
negative charge in another part of the molecule. Molecules like this are
called polar molecules.
The charged particles in an oil molecule are distributed more or less
evenly throughout the molecule. Molecules like this are called nonpolar
Polar molecules like to stick together. That's because positive charges
attract negative charges. So the positive part of a polar molecule attracts
the negative part of another polar molecule, and the two molecules tend
to stay together. When you try to mix water and oil or alcohol and oil,
the polar molecules stick together, keeping the oil molecules from getting
between them-and the two don't mix. When you try to mix water and alcohol,
they mix fine, since both are made of polar molecules.
What's this pretty toy doing in a set of science experiments? It seems
more like an art project to me.
When you make a Glitter Globe, you're experimenting with two liquids
that won't mix with each other--alcohol and oil. Playing with the Glitter
Globe gives you a chance to watch how liquids flow. And in the process,
you make something that's pretty.
Some people think that science and art have very little in common. At
the Exploratorium, we disagree. Both artists and scientists start their
work by noticing something interesting or unusual in the world around them.
Both artists and scientists experiment with the things they have noticed.
Art and science begin in the same place-with noticing and experimenting.