Watermelon vs Potato in Slow Motion - Smarter Every Day 155

Hey, it's me, Destin. Welcome back to Smarter Every Day. I have built a potato gun out of clear pipe, which is amazing because you can see what's going on on the inside of the potato gun. Today's experiment is going to be pretty fun. Please excuse my scratchy voice, but this is my only day off of work.

This is my buddy. What are you going to do to help me? Uhmm, I'm going to trigger the high-speed camera. Destin: Trigger the high-speed camera. That's right. This is the high-speed camera we are going to use to film at about 3000 fps. This is going to be a pretty big explosion, so you are going to need that. We've got our potato ammunition, isobutane propellant (hairspray), watermelon, and large squash.

We're going to put a squash up here, and we are going to hit it with a potato and see how much force we can transfer to that thing. You ready? Should be fun, let's give it a shot. Okay, so the important thing when putting a potato in a potato gun is you want a seal all the way around the potato. There is a fancy word for that. It is called obturation. If you can get a complete obturation seal on the obturator, you can get more compression and more velocity.

So let's see how many Mississippi's we are going to put in here... 3, 2, 1 Alright, let's see. Let's see if it worked. Broke just a little bit, but we can do better than that, can't we? Alright, let's do it again! Okay, that white part all the way around that's touching the barrel on the potato, that's called the what? Obturator. And what does the obturator do? It makes the air not go past the bullet. Destin: That's right. It makes the explosion not go past the bullet.

Ohhh, that was a weak one, wasn't it? We broke the squash. Destin: Did we? I think gravity did that more than the potato, don't you? Let's go look at the high speed, but I think the potato is breaking when it hits the squash, so we might have to make a stronger potato on the front. Okay, the potato is just shattering on impact. So clearly we need to fortify our potato.

So I'm going to drill a hole in it here and put some metal on the front and see what that does. 3, 2, 1 I think that worked... Okay, so the potato kept breaking, right? So we are going to use this. But it is made in a plastic case, so why can we use this in the barrel? Because it has the obturator. That's right. Good for you! That's a big word for a little boy, I'm proud of you.

Okay, let's go get it set up. You hear that seal? It's really good. It's really hard to do it because it's a really good seal. 3, 2, 1 Are you ready? 3, 2, 1, Go! Okay, one quick thing I wanted to point out about the potato gun, it has to do with pressure, volume, and velocity. As the propellant ignites and pressure causes the potato to move down the barrel, when it does this, the volume behind the potato expands.

As the volume increases, if the burn rate doesn't keep up, sometimes the pressure can start to decrease. Different types of potato gun propellant burn at different rates. Depending on the length of the barrel, if the volume expands too much, the pressure inside the chamber can actually dip below atmospheric pressure. The pressure can dip so low, in fact, that it can condense water vapor out of the air.

I'm not 100% sure that's what is happening in this next clip, but it's still awesome. Check it out. That is what you call backyard ballistics. I hope you enjoy this episode of Smarter Every Day. It was brought to you by Audible.com. Before I tell you about the book I've been listening to, I'm going to tell you about the next episode, which is ridiculous.

It's the same combustion chamber, transparent, at night, in slow motion, but I propagate that flame by initiating it at different points inside the combustion chamber. When I saw the slow-mo, I just giggled like a lot. It's really a blast. That was bad, I'm so sorry. Anyway, if you want to see that episode, go click that potato right over there. I think you will really enjoy it.

Back to the sponsor. Audible.com sponsors Smarter Every Day, and this is really easy to sell for me. This is not a challenge because Audible is my happy place. When I get on an airplane, my favorite thing to do is to play a game on my phone and listen to an audiobook. Recently, I'm listening to "A Hitchhiker's Guide to the Galaxy: The Restaurant at the End of the Universe." I really enjoy it.

I've done this for years. I've listened to audiobooks on Audible.com well before they decided to start sponsoring Smarter Every Day. I listen to a bunch of books; these are the ones I have physical copies of, whatever. It's you getting smarter. This is what you call a soft sell. I don't have to convince you; you're smart people; you know why going to audible.com/smarter would help Smarter Every Day.

You also know that listening to audiobooks is smart. Anyway, that's it. There is plenty of stuff to click if you are interested in doing that. If you want to go click that potato and go giggle with me, feel free to do that. I'm Destin, and you're getting smarter every day. Have a good one.

What happens if I start the ignition of the potato gun from the back? What happens if I start from the middle? (laughing)