Category Physics

What are Clouds?

Clouds sometimes look like gobs of whipped cream in the sky. Sometimes they look like soft feathers. But what are clouds?

Clouds are billions and billions of tiny drops of water or ice crystals clustered together. Some clouds are all water, some are all ice, and some are a mixture.

You might think the water drops and ice crystals would be so heavy they would fall to the ground. But they are so tiny that the air holds them up, and breezes keep them floating in the air.

The water that makes clouds comes from the earth. Every day, the heat of the sun dries up tonnes of water from everywhere on the earth. All this water is turned into water vapour, which is water in the form of gas. This gas floats up into the air. But as it rises higher and higher, it begins to cool. When it cools enough, it turns back into water or ice. Then, tiny drops form around tiny, tiny bits of dust in the air. These drops make up the clouds.

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Why don’t all clouds look alike?

There are many different kinds of clouds, and each kind has a name. Most clouds are named after their shape.

The clouds that look like great sheets pulled across the sky are called stratus clouds. These are the kinds of clouds that are closest to the ground. They form when a layer of warm air rolls over a layer of cooler air. Together they form a thick sheet-like layer.

The clouds that look like fluffy balls of cotton or scoops of ice cream are called cumulus clouds. Cumulus clouds that rise high into the air and grow dark and heavy with rain are the kinds of clouds that cause thunderstorms.

The highest clouds of all look like thin, wispy streaks or curls. They are so high up in the air, where the air is cold, that they are made of ice droplets. These clouds are called cirrus clouds.

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What are Twisters?

A thick, dark cloud forms in the sky. Warm air from near the earth rises rapidly towards the cloud. At the bottom of the cloud, the air starts spinning. This wind spins and twists and drops down into the shape of a long tube, or funnel. This wind is called a tornado, or twister.

The funnel may touch the earth’s surface. When a tornado touches ground, it can be dangerous. It can pick up heavy machinery and toss it far. The winds of a tornado rip roofs from houses and uproot large trees.

Tornadoes can happen in many parts of the world. But most tornadoes happen over the central U.S.A. People have recorded whirlwinds about 480 kilometres per hour there.

A tornado is a whirling wind that reaches down from the clouds and touches the ground. But dust devils and sand pillars are whirling winds that go from the ground up into the sky. They are much smaller than a tornado.

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What storm has an eye?

A hurricane is a huge, whirling circle of wind and rain. But in the centre of all this wind and rain, the air is calm. This calm hole is called the eye of the hurricane.

A hurricane begins over the ocean, near the equator, where the air is very hot, wet, and still. The heated air begins to rise and whirl around. As the great masses of the air rise up, towering rain clouds form.

The winds swirl faster in a giant circle around the centre of calm, warm air. The storm is called a hurricane when its winds are stronger than 119 kilometres per hour.

Some people in the path of a hurricane experience what seems like two storms. First, the front of the circle hits. The blowing wind and rushing rain sound like steady thunder.

After the front of the circle passes over, the eye of the hurricane arrives. The wind dies down. The rain stops. The air grows hot and still. It may take an hour or more for the eye to pass over. Then the back of the circle arrives. Once more, the wind blows and the rain pours. Finally, the hurricane passes, carrying the wind and rain to another place.

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How hard is the Wind Blowing?

Wind has many different names, depending on how hard it is blowing. In this question, you will find out how to tell how hard the wind is blowing by watching what it does. And you will learn some of the names we give to the different speeds of wind.

  1. In calm air, smoke rises straight up. The wind is blowing less than 1.6 kilometres per hour.
  2. In a moderate breeze, small branches sway, and dust and paper blow about. Wind speed is 21 to 29 kilometres per hour.
  3. In a strong breeze, big branches sway, and umbrellas are difficult to use. Wind speed is 39 to 49 kilometres per hour.
  4. In a moderate gale, whole trees sway, and it is hard to walk against the wind. The wind speed is from 51 to 61 kilometres per hour.
  5. A fresh gale breaks twigs off trees and makes walking very difficult. Wind speed is 63 to 74 kilometres per hour.
  6. A strong gale can blow tiles off roofs and damage buildings. Wind speed is 76 to 87 kilometres per hour.
  7. A whole gale will uproot trees and often do much damage to buildings. Wind speed is 89 to 101 kilometres per hour.

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How do you explain wind?

Wind

When the air seems calm, and you can’t feel a wind, it doesn’t mean that the wind has stopped blowing everywhere. There are always many winds keeping the air around the earth moving. In one place, there may be a soft breeze from the north. In another place, there may be strong gusts from the south.

Two different winds may blow near the same area at once. Near the ground, one wind may be pushing flags in one direction. But higher in the sky, another wind may be making the clouds scurry in another direction.

The fastest winds are high above the clouds, several kilometres up into the sky. These winds are called jet streams. Often, jet streams are connected. They form one huge, rushing river of wind that circles the earth, sometimes at speeds of more than 320 kilometres an hour. When an aeroplane takes off for a long trip, the pilot may fly into the jet stream because it can give the plane a powerful push.

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