Friday, August 06, 2004

An ocean in the air


As you can see from the photo, I'm sitting in a cloud, which is not at all unusual here in Kerry.

Outside my window a myriad of water droplets are suspended in the air, many thousands of tons of water altogether.

What keeps them there? After all, water is very much heavier than air. Why doesn't it fall?

It does -- sort of.

When a skydiver jumps out of a plane, she accelerates until the force of gravity pulling her down is equaled by air resistance, which increases with her speed. Then she falls at a constant rate, her so-called "terminal velocity."

A feather reaches its much smaller terminal velocity rather quickly, and then drifts languorously earthward. A tiny droplet of mist falls so slowly that its downward motion is insignificant compared to other forces that stir the air.

So the droplets hang there, in a fine Irish mist, waiting to either grow large enough to fall as rain, or to be dispersed by the wind.