A few months ago, my boss brought in this air cannon as a method of showing his class that air has weight or that air takes up space. I just couldn't let this prime opportunity pass up, so I used this thing to make a quick video of me running through the training room, knocking down cups, and it was honestly the most fun I've ever had at work. But in doing that, I missed a key lesson that my boss was trying to pass on to the other texts that lesson being air is stuff and that's what we're gon na be talking about today. So when we think of air, we don't normally think of it.

As a substance or something it's just kind of this invisible thing floating around us, but something that needs to be recognized is that air is in fact stuff. It takes up space and it has mass, and it's actual matter now why this matters, understanding that air is something is a key part of understanding air pressure, because a big part of air pressure is when the earth gives air weight due to its gravity. But the earth can only give air weight if it's something so there's a direct link between air pressure and knowing that air is something I conducted an experiment to help see pressures work together. What I did was I took some fire.

I said I took some fire there we go and I took a bottle. It was a really simple experiment. All I used was a balloon, a bottle and some fire. I guess you could say it was a little time so so I blew up the balloon.

Took some tissue paper set, the tissue paper on fire then put the fire inside of the bottle. Then I put the balloon on top of the mouth of the bottle and and after a few moments, the top of the balloon started to slide its way in through the bottle. Now, why is this happening? It wouldn't fit until the fire came into the equation, so in order to understand what's happening, we're gon na need to go to the whiteboard. You know I said we need to so what we're tempted to think is happening here is dalton's law of partial pressure.

Now Jeff my buddy over here is writing the equation on the board. For us say: hi Jeff, hey guys, I'm Jeff and hit the lost states that within each element in air there's a partial pressure and the sum of those partial pressures equals the total pressure of air. Now Jeff is taking an enormous ly long amount of time. So I'm just gon na send them off and I'll put the equation right here.

So all you can see it now, you're tempted to think that when the oxygen is leaving the system because of the fire you're lowering your total air pressure, just like a math equation. That is wrong, and this is why? Because the laws of thermodynamics tell us that energy can't be created or destroyed, it can only change form so that oxygen is going somewhere. Oxidation tells us it's going into carbon dioxide, which cancels out the loss of oxygen. Thus, the air pressure stays the same so wrong.

That is not what's happening. The air pressure, however, is still decreasing, and let me tell you how Jeff, if you want to come, help write this equation. What's actually happening is due to something called the ideal gas law. What the ideal gas law states is that there's a correlation between something's temperature pressure and volume, the exact equation as Jeff's writing.

It is PV, equals n R T. The PE of course stands for pressure. The V is volume and as moles and R is a constant and then there's T which is temperature. So, as you can see once again, it's a basic math equation.

If you were to increase something on one side, the thing on the other side would increase as well. So, for example, as in the bottle, if you are going to decrease the temperature, because that's what happened - that's what's happening. The pressure as a result would also be decreasing because they're equal to each other, once the fire and the bottle goes out. The temperature inside the bottle starts to decrease and, as the equation tells us, that means that the air pressure is also going to decrease high pressure.

Air is drawn toward a low pressure air, which is why the high pressure entering the balloon is drawn toward the low pressure air in the bottle in the bottle. So I want to take a second to explain how all this stuff we've been talking about today applies to the world of HVAC. Now what we've talked about today is that air is, of course stuff and that better helps us understand air pressure. What we know is that high air pressure is always drawn to low air pressure, and this concept can be seen a lot when we're talking about AC.

For example, we have this blower wheel here, and it creates a pressure differential that causes the air in the room. To force its way in on the low pressure side and then force its way out on the high pressure side, so it'll go up through here and come out of this vent. When it's coming out, it's coming out as high air pressure forcing its way into the room which is full of low pressure, air there is stuff there. You go, it's good enough.