26/02/2013
CHEMISTRY
CLOUDS… HOW DO THEY STAY UP THERE?
Solids, Liquids and Gasses are three very different forms of
matter. Yet all three states of matter of the same substance can exist in the
same environment.
In the photo you can see H2O as a solid, liquid and a gas existing naturally in the same location |
This happens because of the forces that occur between individual
atoms and molecules.
Say in the arctic, with an iceberg at sea, the H2O
molecules are fused together in a crystalline mesh. The water around the
iceberg however, keeps them in a semi interacting liquid state thanks to the
movement of the molecules. While water vapour in the air, is the result of
escaping molecules with high kinetic energy.
(Interestingly enough the Polar Regions have a high relative
humidity. As humidity is a measurement of the % total amount of humidity the
air can take. As it is so cold, there is almost no water vapour in the air, yet
humidity rates can still be high)
This is basic chemistry that we are all reasonably familiar with
from high school.
But an interesting question was asked by the lecturer as to
why do clouds stay in the air?
Clouds are not made up of water vapour.
They are made up of tiny water droplets and crystals of ice suspended
in the air… How do they stay up there?
The answer is just as the tiny bits of dust you see dancing
in a beam of light coming into your room in the morning are kept airborne, so
too are the tiny droplets and crystals of water.
These droplets and crystals are so tiny that their density (and therefore gravitational pull)
is not enough to overcome the rising heat from the planet below. This rising hot air pushes with pressure upwards. As the temperature
of the air cools and this pressure decreases, the droplets will hang lower and lower in the sky. Also, as the temperature of the cloud itself cools, the molecules will clump together in larger and larger droplets until gravity overcomes the upwards pressure and they fall as rain.
It also explains why clouds that are very high and very cool
are wispy cirrus formations and clouds hanging low to the earth near the
heat source are your large dark cumulus clouds.
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