Wind and Air: A Mixture Around Us

Read a model of dry air without treating air as pure oxygen.

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Air is a mixture. In a rounded model of 100 parts of dry air, about 78 are nitrogen, 21 oxygen and 1 other gases. Water vapor varies, so this count is for dry air. The symbols are not actual-size particles.

Worked example

In the picture, nitrogen has the largest group. Oxygen is important even though it is not the largest group. The three rounded amounts add to 100.

One hundred model symbols show rounded dry-air proportions: 78 nitrogen, 21 oxygen and 1 other gases. Water vapor is variable and excluded from the dry-air count.

Would you believe it?

Most dry air is nitrogen, not oxygen. A rounded picture of 100 parts has about 78 nitrogen, 21 oxygen, and one part other gases. Water vapor adds a variable amount.

NASA: what air contains

Question 1 Which gas has the largest share in the model? Nitrogen Oxygen All gases have equal shares

Question 2 About how many parts out of 100 are oxygen? 78 100 21

Question 3 Is air the same as pure oxygen? Only if it is moving No, it is a mixture Yes, always

Question 4 Why does the caption say dry air? Water vapor varies and is left out of this count Air never contains water vapor Dry air has no gases

Question 5 What is the total of the three rounded groups? 99 121 100

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