Ng -
To understand the answer to your question, you first have to
understand a little bit about the states of matter: solids, liquids,
and gases. Regular water is a liquid, but if you cool it down it will
turn into a solid (ice), and if you heat it up it will turn into a gas
(steam).
Solids like ice are very stiff because all of the molecules inside
of them (the little tiny bits of stuff that they're made of) are stuck
together very tightly. And gases like steam take up a lot of space
because the molecules inside aren't stuck together at all - they just
fly off in every different direction.
But liquids like water are right in the middle. The molecules of
water are stuck together, but not very tightly. So a single water
molecule might be stuck to another molecule at one instant but let go
quickly and stick to another in the next instant. You can think of it
as if all the water molecules are sliding around across and over each
other all the time.
Just like anything else, when gravity pulls the water molecules
downwards, they will fall. But if they're in a container, the container
will keep them from spreading out completely. This is what's called
'taking the shape of the container'. People say that liquids take the
shape of their containers because they are stuck together enough to not
go flying off like gases but not so tightly that they stay in a stiff
shape like solids do.
One other thing that's pretty cool about how liquids work is
something called a 'meniscus'. If you look at some water in a glass or
plastic cup, you may notice that the water sort of curls up at the
edges. This is because it's very easy for water to stick to plastic or
glass, pulling the water up a little bit along the edges of the
container.
-Tamara
(published on 10/22/2007)
