Properties of Air: Definitions & Explanation

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  • 0:03 What Is Air?
  • 1:08 Mass and Mixture of Gases
  • 2:03 Pressure and Weight
  • 4:16 Air Can Be Compressed
  • 4:42 Air Is Impacted by Temperature
  • 5:36 Lesson Summary
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Lesson Transcript
Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

Air is all around you, but there's more to this invisible gas than meets the eye. This lesson will delve into all of the unique characteristics of air as well as give some examples that illustrate these characteristics.

What Is Air?

You probably don't think too much about air, but it's all around you. It takes up space and is pushing on you right now. There isn't air in space, and if you were to suddenly find yourself in the middle of space without a spacesuit, you'd be aware of how important air is to your survival. Obviously, you need the oxygen to breathe, but if there isn't any air to push on you, bad things start to happen. For starters, bubbles would form in your bodily fluids, and you would double in size. Yikes. Let's get a spacesuit on you ASAP!

So… what is air? Air is a mixture of gases, water vapor, and other substances, and it has specific properties, or characteristics.

  • Air is made up of gases
  • Air has mass
  • Air exerts pressure and has weight
  • Air can be compressed
  • Air is impacted by temperature

Wow, that's a lot of new terminology! Let's check out each point on that list.

Mass and Mixture of Gases

Mass is defined as how much stuff an object contains - and by stuff, I mean matter, like atoms and molecules. And even though you can't see it, air has a lot of atoms and molecules. Air is a gas (as opposed to a liquid or a solid) and contains about 78% nitrogen, 21% oxygen, and 1% argon. There are other trace gases in air, like helium, carbon dioxide, and neon, just to name a few.

Air also contains water vapor; the amount varies depending upon the location (think tropical, humid Hawaii versus the dry desert of Las Vegas). Finally, air contains other things, like dust, pollen, and bacteria.

What proof is there that air has mass? Well, if you blow up a balloon with air, the balloon expands. It's expanding due to the gases, water vapor and other materials that give air mass.

Pressure and Weight

Let's move on to pressure, or when something exerts a force on something else. All of those atoms and molecules we just mentioned are moving all around you. The pressure you're experiencing right now is due to all of those atoms and molecules bumping into you, as well as the weight of all of the air molecules and atoms above you.

And how do we know those atoms and molecules have weight? If you were to weigh an empty balloon and then fill it with air and reweigh it, you'd notice it gained weight. This is because, as long as there's gravity, everything with mass has weight (including air).

And here's a fun fact: at sea level all of the air above you exerts 14.7 pounds per square inch on your body (as well as everything around you). If you're below sea level, the number is greater (because you have more air pushing down on you) and if you're above sea level, this number is smaller (because you have less air pushing down on you).

If you take your whole body surface into account, that's about the weight of a small car bearing down on you at all times. Whoa. So why aren't you crushed? First off, air is exerting this pressure all over you and it evens out.

Secondly, our bodies are built to endure this pressure. The pressure from the air inside of our organs, like our stomachs and lungs, is pushing outward and this balances the pressure from the air outside of our bodies pushing inward, so we don't collapse.

What happens if you take us out of our normal pressure? Remember, if you were to find yourself in space without a space suit, the internal pressure of your body would be greater than the external pressure (remember: no air means no pressure pushing in on you), so you would double in size. Fortunately, your skin is really stretchy so you probably wouldn't explode. And without the air pressure from Earth, gases that are dissolved in your bodily fluids turn back into a gas, creating bubbles. These bubbles can get lodged in blood vessels, causing all sorts of problems.

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