Why do clouds float

Upward vertical motions, or updrafts, in the atmosphere also contribute to the floating appearance of clouds by offsetting the small fall velocities of their constituent particles. Clouds generally form, survive and grow in air that is moving upward. Rising air expands as the pressure on it decreases, and that expansion into thinner, high-altitude air causes cooling.

Enough cooling eventually makes water vapor condense, which contributes to the survival and growth of the clouds. In both cases, though, the atmospheric ascent is sufficient to negate the small fall velocities of cloud particles.

Another way to illustrate the relative lightness of clouds is to compare the total mass of a cloud to the mass of the air in which it resides. Consider a hypothetical but typical small cloud at an altitude of 10, feet, comprising one cubic kilometer and having a liquid water content of 1.

The total mass of the cloud particles is about 1 million kilograms, which is roughly equivalent to the weight of automobiles. But the total mass of the air in that same cubic kilometer is about 1 billion kilograms, times heavier than the liquid!

So, even though typical clouds do contain a lot of water, this water is spread out for miles in the form of tiny water droplets or crystals, which are so small that the effect of gravity on them is negligible. Thus, from our vantage on the ground, clouds seem to float in the sky.

Sign up for our email newsletter. An object in a fluid floats when the object is less dense than the fluid. For two objects with the same volume, the denser one weighs more. Clouds are made of air and small water droplets or ice particles, as well as some water in its gas phase, called water vapor.

The water droplets scatter all the colors of light from the sun the same amount and give the cloud its white appearance. There seems to be some disagreement about whether a cloud is less dense than the surrounding air at the same temperature and pressure — it depends on the type of cloud and the ratio of liquid water to water vapor in the cloud. So, I am not sure whether the cloud floats in that sense.

NASA says that a typical cloud is about one cubic kilometer in volume and has about one gram of water per cubic meter. Forgetting about wind for a minute, a water droplet feels a downward force from gravity and a resistance or drag force due to the air that the droplet has to push out of the way in order to fall. Cosmos » Climate » Why do clouds float?

Clouds must have weight, because water has weight. The liquid droplets are about 0. Some of these tiny droplets are so small that it would take a billion of them to make a single raindrop.

Different clouds carry different amounts of water. After all, cloud shapes and sizes can range from thin, wispy cirrus, right up to monstrous cumulonimbus thunderclouds.

A typical cumulus cloud carries about 0. But the whole cloud might be one kilometre by one kilometre by one kilometre. So it could carry up to about tonnes of water. There are three main reasons. First, the heat of the Sun warms the ground, which then creates rising currents of air.