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Uploaded:2012-11-20
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Watch Punkin Chunkin this Thanksgiving, November 22nd, at 8 pm on Science Channel.
More pumpkin carnage online at ScienceChannel.com/chunk

"Punkin Chunkin" is the United State's annual contest to see whose homemade machine can hurl a pumpkin the farthest (without explosives!). Every November, thousands of amateur engineers converge on a farm in Delaware to put their contraptions to the test. The machines at the Punkin Chunkin festival rely on physics to get the pumpkin airborne & Hank is here to give you all the fascinating details of how it works. Happy Thanksgiving!

Thanks to Science Channel for helping with this episode and giving us some money and footage to produce it.

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References for this episode can be found in the Google document here:http://dft.ba/-2Mx4
All footage used with permission from Science Channel.
[Opening theme music]

Are you like me? Do you like watching fruit explode and also enjoy physics?  Well if so, there's probably only one place in the world where those two great tastes come together: Punkin' Chunkin! America's annual contest to see whose homemade machine can hurl a pumpkin the farthest.

Every November, thousands of amateur engineers equal parts da Vinci and Gallagher converge on a farm in Delaware to put their contraptions to the test. They compete in divisions based on what kind of machine they've built and whoever's device hurls their squash the farthest wins. The only rule, no explosives. Yeah I know, a little bit disappointing there. But never underestimate physics; when it's awesome powers are unleashed it can make even a seemingly simple machine cause a lot of squash damage, and look good doing it.

The machines at the Punkin' Chunkin' festival rely on the release of stored energy to get the pumpkin airborne. This energy comes from some external force that's exerted on a part of the machine where it's been pent up as potential energy. For example there are the air cannons which release all at once the potential energy of gas that's been slowly pressurized inside a container, and then there's what the contest calls centrifugal machines where a motor spins the pumpkin around a tether which is pretty cool, even though centrifugal force is not a thing.

From where I stand, the most delightful Punkin' Chunkin' physics are found in the class of machines that you probably know as catapults. Yes, they're not just for smashing castles or "apulting" cats, (meowww) there are actually many different kinds of catapults including the mangonels, trebuchets, and torsion machines, each using a slightly different sort of force to create the potential energy.

When you're thinking of a catapult, what you're probably seeing in your head is a mangonel. It's main feature is a long beam with a bucket on one end and the other fastened to an axle. The bucket end of the beam is usually attached to a sling by the machine's main frame, then it's pulled down to apply the force of tension, this tension is what stores up the machine's potential energy until it's released. For Punkin' Chunkers though, catapults can use springs, cords, rubber, or dead weights to apply tension, but they've added an extra touch of genius to the traditional mangonel. Instead of just a bucket on the end, what it has is a sling. What's the genius in that? Well it gives the machine a second fulcrum, or pivot point, the first fulcrum being where the machine meets the axle. But when that's released it throws up the sling, which amplifies the power of the first fulcrum.

This is all very similar to how trebuchets work, but they're a little more sophisticated, you know, as far as catapults go. Rather than holding all the potential energy at the tip of the beam, where the pumpkin is, trebuchets rely on a counterweight at the other end. Again, the beam is pulled down to set the device but instead of tension being the force at work here, it's simply gravity. The heavier your counterweight is and the higher you lift it, the more force you get out when it falls. As a result, trebuchets are much more efficient, they tend to shoot a lot farther, and are more accurate giving you more chunk for your buck.

Finally you have what the hardcore chunkers call torsion machines. Most of these kinds of catapults are hybrids of the first two. They have a sling at the pumpkin end, just like a trebuchet, but instead of gravity they use the force of tension like a mangonel. Unlike with a mangonel though, this tension is applied to this machine by twisting a length of rope around the bottom of the beam. It's the same idea as twisting a rubber band on a propeller toy airplane. The twisting, or torsion, is just tension applied in a rotating direction instead of just straight up and down. And we all know what happens from there.

But please don't try this at home, unless you have a scale model or something, just watch from the safety of your sofa, don't miss Punkin' Chunkin' this Thanksgiving November 22nd at 8pm, only on Science Channel. And for more pumpkin carnage, check out sciencechannel.com/chunk for videos from this year's Punkin' Chunkin', and high-speed footage of various foodstuffs getting the crap blown out of them. And of course, Happy Thanksgiving. 

[End theme music]