Most normal people have, at some time in their lives, laid on their back in the grass and looked up at the summer sky as clouds drift slowly over. Often we play games of finding familiar shapes in those clouds. But have you ever wondered how much a cloud weighs?
At first thought, that would seem to be a nonsensical question: obviously, it doesn’t weigh anything because it’s floating in the air. But if you think that through a bit more, you’ll see that this claim doesn’t hold water.
What are clouds made of? They’re mostly air and water in some form or another. Generally this would be water vapor. Think of it as cold steam. The droplets are so tiny, they can ride eddies and currents of air that constantly swirl about in our atmosphere. Dry air is also denser than water vapor, so it will buoy the clouds up until the vapor turns to larger droplets (rain) or freeze into snow or hail.
It is a common sight here in the Great Smoky Mountains to see fog banks that form overnight along creeks and rivers be lifted up the slopes of the mountains as the morning sun warms the trees, which warm the air, which rises. As the warmer air rise, it drags these fog banks with it, up the slopes, to the mountain crest, then they launch; changing from fog to cloud (which is essentially the same thing except for location).
Water has weight: 8.34 pounds per gallon at room temperature. So if clouds are made of water, clouds must have weight. Can we calculate the weight of a cloud?
