Why Do Clouds Look like They’re Floating? The Science Behind the Illusion

SPACE — Look up at the sky and clouds can look like canyons of feathers or giant ice cream castles in the air. They look like they are floating and staying suspended in the sky.

So, what makes clouds look like they’re not falling?

According to Alex Lamers, a meteorologist with the National Weather Service, clouds are not actually like pillows or something that magically floats in the air. “(what we see) is a kind of illusion,” he told Live Science.

Clouds are collections of water droplets and ice crystals. The droplets form around cloud condensation nuclei, which can be specks of dust or salt. When clouds contain too much water, water falls in the form of rain, snow, or hail.

Also read: Looks light and fluffy, how much do clouds actually weigh?

However, Lamers said, even before the rain falls, the droplets are moving towards Earth, albeit at a slow speed. “They fell very, very slowly,” he said.

Everything that falls to Earth reaches what is called terminal velocity, or the fastest speed possible during free fall. Terminal velocity occurs when the pulling force of the air completely opposes gravity.

However, the water droplets are so light that their terminal velocity is very slow, namely between 18 and 36 meters per hour for droplets with a radius of 5 to 10 microns. Because clouds are usually thousands of meters high in the atmosphere, that small downward shift is invisible to our eyes.

Lamers gave the example of water droplets falling from clouds (not when it rains) as similar to dust grains swirling in the sun. However, the water droplets are still smaller. According to Mark Miller, professor of atmospheric sciences at Rutgers University, the average size of a water droplet in a cloud is smaller than the radius of a human hair.

The slow descent of the cloud water droplets is still further hindered by the upward flow of air, which makes the illusion then appear. That airflow keeps the fused droplets suspended, even as they slowly fall.

“They appear to be floating because essentially, they are falling at a speed that is slower or equal to the speed of the updraft in the cloud,” Miller said.

Miller said the particles fell and rose simultaneously. Therefore, water droplets can act as tracers of air movement. This means that the rising air pushes millions of droplets into its path, thus forming the clouds we see.

Also Read: Neptune’s Clouds Disappear, Allegedly Due to Solar Activity

But what plays a role is not just falling and rising simultaneously. Although clouds appear at a relatively fixed height, they fluctuate as rising air mixes with water droplets that condense and evaporate.

2023-10-28 20:11:00
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