WEBVTT - How Contrails Work

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<v Speaker 1>Welcome to brain Stuff from how Stuff Works dot com

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<v Speaker 1>where smart Happens. Hi, I'm Marshall Brain with today's question,

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<v Speaker 1>why do those long white clouds formed behind jets flying

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<v Speaker 1>high overhead? The clouds that jets form on certain days

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<v Speaker 1>are called condensation trails, or contrails. Some days the contrails

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<v Speaker 1>will form thin lines that cross the entire sky, other

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<v Speaker 1>days they will be much shorter, and on some days

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<v Speaker 1>there won't be any at all. A contrail forms because

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<v Speaker 1>one of the components of jet engine exhaust is water.

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<v Speaker 1>Jet fuel is made of carbon and hydrogen. When jet

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<v Speaker 1>fuel burns with oxygen, most of the exhaust consists of

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<v Speaker 1>CO two or carbon dioxide, and H two O or water.

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<v Speaker 1>A big jet burns hundreds of gallons of fuel per hour,

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<v Speaker 1>meaning it produces hundreds of gallons of water. The water

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<v Speaker 1>is generally an invisible vapor. When you exhale, your breath

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<v Speaker 1>contains a great deal of invisible water vapor as well.

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<v Speaker 1>You may have noticed that on certain days in the winter,

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<v Speaker 1>your breath will form a cloud of condensation when you exhale.

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<v Speaker 1>In the summer, however, you don't see your breath. You

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<v Speaker 1>see the condensation in winter because cold air can hold

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<v Speaker 1>a lot less moisture than warm air, so in the winter,

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<v Speaker 1>when the moisture in your breath hits the cold air,

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<v Speaker 1>the moisture condenses into a visible cloud. The same thing

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<v Speaker 1>happens when a jet engine exhales. If the temperature, winds,

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<v Speaker 1>and humidity in the upper atmosphere are right, long white

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<v Speaker 1>trails form when the moisture in the exhaust condenses. For

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<v Speaker 1>more on this and thousands of other topics, does that

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