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Hank uses a favorite subject of the YouTube community - the potato gun - to teach us about the principles of pneumatics, which use the potential energy of compressed gas to do work in lots of useful machines every day.

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References and licenses for this episode can be found in the Google document here: http://dft.ba/-4f05
Remember that video of Obama shooting a marshmallow out of an air cannon at the White House? That technology basically works the same way as those tubes at the bank drive-through that shoot money at you. Or nail guns, that shoot nails at you. Not at you. At wood.

Those and other awesome machines are brought to you by the principles of pneumatics, which use the potential energy of compressed gas to do work. Since air is cheap, plentiful and non-toxic, a lot of machines use pneumatics, by simply pressurizing air and then letting it loose to move a bank canister, or a nail, or a marshmallow.

It's also the same technology that lets me fire this whole chunk of apple at you. Ooh! That same thing, of course, it's actually better to do with a potato, but we only had an apple lying around the office, and YouTube is of course full to the top with videos about how to make potato guns, or even potato cannons. But I'm not about to start you off on a path that involves a can of hair spray and a lighter. You can put an eye out.

In order to make this humble potato/apple shooter and demonstrate pneumatics safely in your own home, all you need is a ball point pen and an apple or potato.

You just take the writey part of the pen out of the pen, and remove the cylinder thing, and take the cap off, and then you shove it into your potato. Alright, something like that. Pull it out. Try and get your chunk like a nice seal on one end and then stick it in the other side. You can use this thing as your plunger, and you just shoot it!

It's not the most exciting thing we've ever done in SciShow, but the principles at work in our little shooter are the same as in all pneumatic devices, and in order to understand them, you first have to understand the properties of gases.

Gases, technically, are fluids. Substances that reshape themselves to whatever container they're in, and there are lots of laws that dictate how fluids work here on Earth.

For starters, there's Pascal's Law, which says that when there's any increase in pressure - that is, the amount of force being applied to a particular area - at any point in a contained fluid, an equal increase in pressure is exerted at every other point in the container.

Blaise Pascal, a French mathematician, figured this out in 1646 by pouring water down a pipe into a wooden barrel that was already full. Instead of the water just running up out of the top of the pipe as you might expect, the barrel exploded.

The way that the water being poured in increased the pressure on all sides of the barrel leading to a kablamo!

So on our apple shooter, when I push on the chunk of apple, the gas between the two chunks is exerting the same amount of pressure on both of them, as well as on the walls of the cylinder. Anything within this contained system is experiencing the same amount of pressure.

But why does pushing on it create more pressure in the first place? Well, that's where another important law comes in, the Ideal Gas Law. This states the amount of pressure and volume of a gas have an inverse relationship. As the volume of a gas goes down, the pressure goes up. And vice versa.

This is only true as long as the temperature of the gas remains constant, by the way. Since temperature, volume and pressure of the gas all factor into a gas's state at any given time.

So when I decrease the volume of the air in the cylinder by pushing the plunger in, I'm creating more pressure inside it. Now, if I want, I can push the plunger in only part-way, and then stop. Once the air is compressed, it has potential energy to do work. But as I keep compressing the air, the pressure gets even higher, and at this point, the only thing keeping the other apple chunk in the cylinder is friction.

Once the force of the pressure becomes greater than the friction that chunk starts moving, and the more it moves the more friction drops until it's airborn. So yes, simple. But also pretty awesome. Physics can be like this apple. Easier to digest in small portions.

Thank you for watching this SciShow experiment. If you have an experiment or demonstration that you'd like to see us do, let us know in the comments below. We're also on Facebook and twitter. And if you want to keep getting smarter with us here in SciShow, you can go to http://www.youtube.com/scishow and subscribe.