The movement of hot and cold air is very
important for moving heat and energy around our
planet Earth. Hot air is less ‘dense’ than
cold air. In case you do not know the word ‘dense’
yet, I essentially mean that hot air is lighter
and cold air is heavier. Therefore, hot air rises
and cold air sinks. Now, what happens?
Perhaps you know that when you go up mountains or
up in an air balloon or air plane it gets cold
outside. For every 1000 meters in elevation, the
temperature typically falls by 6.5°C. So, as
warm air rises, it gets colder and colder.
Therefore, the warm air cools. Similarly, when
cold air falls it gets warmer. Of course,
wherever air moves away, there has to be some
‘other’ air that moves into place where the air
was before. Otherwise, we would have places
So, air moves around in a BIIIIG
circle: Hot air rises, and is replaced by cold
air. The warm air gets cold, and moves, and
eventually falls again when it gets cold enough.
This is what makes wind on the earth.
Big things happen when the air holds
water. Yes, air can ‘hold’ water. For example,
sometimes before a thunderstorm you feel that the
air is really “sticky” or “humid”, that is
because there is a lot of water in the air. Or,
when you boil water, there is steam (very small
water drops) that come out from the water and that
disappear in the air. The water is not gone.
It is just ‘in’ the air. Now, the important thing
is that warm air can hold more water than cold
air. Therefore, when warm air rises, the air
may not be able anymore to hold all the water that
it has. Then the water will come “out of the air”
and form very tiny drops– this is a cloud. If
there is a lot of water, the drops can get bigger
and bigger until they are heavy enough that
they fall from the sky – it rains. So,
the movement of cold and hot air brings all
weather to the planet. It makes wind, and rain,
Click Here to return to the search form.