Air doesn't seem to be made of any thing. It has no color, taste, or smell. And you can see right through it. But it is made something. It is made up of many kinds of gases. And these gases are made up of tiny, tiny, things called molecules.
Actually, everything is made up of molecules - rocks, plants, animals, water, and gases. The molecules in a rock are packed close together and hardly move. The molecules in a liquid, such as water, are farther apart and move rather fast. But the molecules of a gas are quite far apart and zip about rapidly. That's why gases are so "thin" and invisible.
For us, the most important of all the gases in the air is the one called oxygen. The only reason we breathe is to get oxygen into our bodies. We couldn't live without it. Almost every kind of animal and plant in the world must have oxygen or it will die.
Only about one-fifth of the air is made up of oxygen. Most of the air - nearly four-fifths of it - is a gas called nitrogen. The rest of the air is made up of many different gases.
There is also a great deal of water vapor and bits of dust floating in the air. But these things are not really part of the air itself.
If air is just thin, floating gases, why doesn't it drift away into outer space ? What keeps the gases from just floating away until they are gone ?
The answer to that is gravity. Earth's gravity pulls at all the molecules of air, just as it pulls at you. The air can no more float off into space than you can !
Actually, everything is made up of molecules - rocks, plants, animals, water, and gases. The molecules in a rock are packed close together and hardly move. The molecules in a liquid, such as water, are farther apart and move rather fast. But the molecules of a gas are quite far apart and zip about rapidly. That's why gases are so "thin" and invisible.
For us, the most important of all the gases in the air is the one called oxygen. The only reason we breathe is to get oxygen into our bodies. We couldn't live without it. Almost every kind of animal and plant in the world must have oxygen or it will die.
Only about one-fifth of the air is made up of oxygen. Most of the air - nearly four-fifths of it - is a gas called nitrogen. The rest of the air is made up of many different gases.
There is also a great deal of water vapor and bits of dust floating in the air. But these things are not really part of the air itself.
If air is just thin, floating gases, why doesn't it drift away into outer space ? What keeps the gases from just floating away until they are gone ?
The answer to that is gravity. Earth's gravity pulls at all the molecules of air, just as it pulls at you. The air can no more float off into space than you can !
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