Example of a stable and an unstable equilibrium, respectively.
Click on image for full size
Have you ever tried to balance a long stick on your hand? Hard, isn't
it? That's because the stick is part of an unstable
system. If the wind pushes the stick a little bit, it will keep going in
that direction. If you hold the stick upside-down it's much easier to
keep straight. That's because when the stick is held from above it's a
system. If a breeze moves the stick, it will
come back to its starting position.
The atmosphere can also be stable or unstable. If it's unstable, then clouds
can form. The
more unstable the atmosphere is, the more severe
the weather can
be. Clouds and storms form when pockets of air rise and cool because
they expand in the lower pressure
of the upper atmosphere. The air
pockets become saturated and the water vapor condenses to form clouds.
These air pockets don't rise because they want to; something needs to give
them a push. This is called the lifting mechanism
there is no lifting mechanism, no storms will form regardless of how
unstable the atmosphere is. The more unstable the atmosphere, the less
of a lift is needed. It's similar to trying to balance a stick with a
smaller and smaller cross-secion. A log is easier to balance on end than
a twig and the twig is easier to tip over--it's more unstable.
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