The Physics of Slingshots, with Jörg - Smarter Every Day 31

Hey, it's me, Destin. Welcome to Smarter Every Day. Today we—
(Jörg) Nope. [Chuckles] Welcome to the Slingshot Channel. [Laughs]
(Destin) As you can see, today I've been taken over by Germans. We're going to look at slingshots today. The physics of slingshots. So why do they call your channel the Slingshot Channel? I don't understand.
(Jörg) You know, I don't understand either. You know, you would think that we'd call it the Nice Guys Channel or something like that, so... No, they called it the Slingshot Channel. - I think it makes sense. [Both laugh]

We're going to talk about the energy use in bands. Do you want to say anything about it?

• Yes. Well, this is of course the lightest slingshot that I've ever built. [Both laugh] Not exactly. It's actually the most powerful one. The energy of a rifle shot, and it has the momentum of a sledgehammer.
• Alright, so we'll do the math and see if Jörg is right. So let's look at the physics of slingshots. Kinetic energy is 1/2 mass times velocity squared. For a .22 it's about 153 joules, but for a Springfield .30-06 it's 3841 joules. I calculated the momentum of a sledgehammer by smashing bricks in the backyard and analyzing the high-speed. It worked out to about 46 newton seconds.

There is an angle between the band and the point of anchoring. This angle... I'm not going to get my hand in there, 'cause I don't want to die. But this angle... if you take the cosine of that angle, that is the amount of force going into accelerating the projectile. So the closer the bands, the more efficient the slingshot. Is that correct, Jörg?

• Yes, exactly.
• Yeah, this is as awesome as it looks. [Click, wooden clang]

(Jörg) So because it's rather cold now, and also we kept the bands in drawn-out condition for quite a while, the shot went low a little bit because the rubber was a little tired already, and in cold weather rubber doesn't work as well as in hot temperatures.

• Ah. Makes sense. It was almost a complete momentum transfer between that ball and the wood. The mass-times-velocity of the ball went all into the wood. So the mass-times-velocity of the wood after the shot would be equal to the ball. [Music]

[Man speaks German] [Click, splat]
(Destin) Yes! [Laughs] [Music] So I'm Destin, and you are getting smarter every day. And if you want to, go check out Jörg's channel - the Slingshot Channel. Yeah?

• Yes. Make sure. So I'll put a link for you to click, so go to his channel and if you like it, subscribe. That's it. Bye.

(Jörg) This is the only slingshot that I've ever built that makes grown men giggle like they're small girls. [Both laugh] - Okay, slingshots are all about turning potential energy into kinetic energy. So the first thing we have to do is we have to build up the potential energy, so Jörg is doing that now... with his sissy device.
[Destin giggles] That translates, right? [Giggles]
(Jörg) Pretty much. And I will soon be done here, so...

• So I'll have to start running. So this is a very, very large steel ball, clasped here between the dowels, and we're going to try to destroy this pumpkin. The pumpkin really has no chance. It's just a question of if we can hit it.

Captioning in different languages welcome. Please contact Destin if you can help.