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Science Around Us – Clouds 1 – Why Are Clouds White

A group of small clouds passing by

Clouds are made up from millions of tiny water droplets that float in the air. The sunlight that shines onto them is a mixture of the rainbow colours which makes the light white. This white light shines onto the droplets and they behave like millions of tiny mirrors reflecting the white light in all directions. The reflection of the light makes the clouds appear white.

Pippa gathered some equipment and materials to make a model cloud.

Pippa in her kitchen lab

She poured some olive oil into the water. In this model the water represents the air and the oil represents the material (the water droplets) in the cloud.

The oil and water ready to be mixed

Pippa stirred up the oil and water. As oil and water do not mix, the oil began to form tiny droplets in the water.

Pippa stirred up the oil and wate

As Pippa stirred the droplets became smaller and smaller until they behaved like the water droplets in a cloud and reflected the white light in the kitchen in all directions.

Pippa’s model cloud

How do clouds stay up in the air?

The billions of water droplets that make up a cloud are smaller in diameter than a hair on your arm. If you could scoop up part of the cloud shown in the first picture and put it in a box measuring one metre square (or about the size of a kitchen fridge) and measure the weight of all the water droplets in it you would find they weighed about as much as one baked bean. This means they weigh very, very little and any upward movement in the air (such as wind or rising air from the warm ground) will keep them in the air.

Next topic – Clouds 2 – How are clouds made?

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