Air is not nothing. Since we can see through air and are mostly desensitized to the weight of its mass constantly pushing down on us and surrounding us, we can easily be lulled into the misperception that air is empty – comprised of nothing. But that’s not true. In fact a cup of air has more atoms than a cup of water. When we pour water into an empty cup it’s not actually empty. It’s filled with air atoms that are then displaced by the heavier water. Water flows in, air gets pushed out.
Air atoms are what make airplane flight possible, by the way. The air atoms traveling over the top of a curved wing move much faster than the air atoms traveling under the near flat wing. This causes a decrease in pressure on top of the wing allowing for lift. Here’s a tip for you aeronautical engineers out there: if you can find a way to slow down the air under the wing then the lift will become greater and easier. Just saying. Why do the “next step” processes in scientific advancement sometimes take decades or centuries? It’s like we are all having collective brain farts. It only stands to reason that if the faster air on top of the wing increases lift then slowing or compressing the air underneath the wing would increase lift also. But I digress.
Air atoms are striated in our atmosphere too, like aged bourbon in an oak barrel. If you open a bourbon barrel after 12 or 15 years you will see that the lighter materials – especially dangerous and very light alcohols like methanol – have settled toward the top. And the heavier materials like darker bourbon and particulate matter settle toward the bottom.
Air does the same thing. Lighter atoms settle toward the top of the atmosphere and heavier atoms settle toward the ground. So air is striated by weight.
The big question, at least in my mind, is why do things striate by their “heaviness?” Scientists and laymen like myself have argued this question ad infinitum, or until the cows come home. The bottom line is simple though: we all agree that there is something pulling on atmospheric atoms from earth in order to keep them in our atmosphere. Some sort of force is keeping the water in our lake beds and ocean beds.
Of course, duh, every sixth grader knows that the force holding things onto the planet is gravity. The problem is that gravity is – as of yet – unexplained. We enjoy a simplified understanding of what gravity does. We just don’t know how it does it. Which is OK for now.
Again, it’s not entirely true that the Earth’s gravity holds atoms in place. We know for example that thousands of metric tons of hydrogen atoms escape from the Earths atmosphere every year and float off to some other gravitational pull. My guess is towards the Sun or Jupiter, the two largest bodies of mass in our solar system.
It doesn’t matter though because it will be replaced eventually. What’s important is why hydrogen floats off. And that’s pretty easy too. Hydrogen is the lightest element at 1.007 atomic weight units. So naturally in a gravity situation it gets “displaced” to the top of the atmosphere. Helium is another story. At 4.002 atomic weight it will be less likely replaced because of it’s weight, among other things. Among them is the fact that helium does not react with other molecules to form molecules, and therefore will not get “weighted down.” The only reason we have helium is that it is trapped under geologic formations. Once released it will float off into space like it’s lighter hydrogen counterparts.
Why can we see water? Because we would drown if we couldn’t see the difference between air and water. It’s a survival thing.
I try to get around making mistakes on environmental math by thinking of air as a liquid, – lite style. And there are different layers of air too, depending on how high it is. For instance, oxygen is hard to find above certain altitudes. So the “oxygenated layer” is pretty much constrained to being down here with us Earth walkers. Above that is another, lighter layer. And above that is another, lighter layer. etc., etc….. It doesn’t take a rocket scientist to figure out that turbulence is just the jagged waves on top of one layer where it meets the next, upper light layer. “Waves? I don’t see no stinkin’ waves!” Well, that’s pretty much my point. We can’t see them.
So why are layers separated by their lightness, or weight? Well, most people explain that with the word gravity. The problem there is that gravity, in fact, is only a word. It’s not a definition.