Why Snatch Blocks are AWESOME (How Pulleys Work) - Smarter Every Day 228

• Hey, it's me, Destin. Welcome back to Smarter Every Day. It's time for the pulley episode. These are like my favorite things in the whole world. I bought this one; it looks like it goes to a boat or something like that. Pulleys are one of these things that everybody knows about. They know that somehow, a pulley will give you mechanical advantage, but people don't really understand it. We all pretend like we do, but the person that really shows up and is really clever, and they arrange it in the perfect way, and they just make things work, that's like the smart person that everybody wants to be.

So today, on Smarter Every Day, we're gonna make a video about pulleys, and we're gonna slowly walk through how they work. And specifically, I wanna introduce you to my favorite type of pulley; it's called the snatch block. They're really fancy; they can do tricks. Okay, let's start by picking up these cinder blocks. My kids are gonna show you how to pick up blocks, right? If you have to pick something up, you have to pick up all of the weight of the thing and, whether you know it or not, all of the weight of you.

How you doing, good? - Good. - You can put it back down. How hard was that? Not that bad? The magic of a pulley is really the magic of a rope, because a rope is always in tension; you can't push a rope. If you pull on this side of the rope, that force transfers all the way through the pulley, so you basically can redirect the force. That is the primary function of a pulley: redirecting force. (child grunts) That's pretty good, how was it? - Hard. - The pulley changes the direction of your body weight, so you can use your own body weight to help you pick something up. Very good, was that hard? Not as hard. - Not as hard. - Not as hard as what? - Just picking it up. - Okay, so it's easier to pick it up with the pulley because you can kind of lean into it, right? - Yes, sir. - Right.

So this is the part that starts to confuse people. If you can change the way the pulleys are arranged, you can make it even easier to pick this up. Do you want the normal pulley or the snatch block? - The snatch block. - Snatch block! There you go. (pulley clacking) Go for it. So you split it apart; don't cut your finger off there; there you go. So this is the magic of a snatch block. We can put a pulley in any place at any time as long as there's a rope and the snatch block is big enough for the rope.

This is the part where, when you see it happen, you're like, "Oh yeah, of course it's easier because of pulleys." But if you don't stop and think, you won't really understand what's happening. So slowly pull; is it really easy this time? - It's a lot more easy. - A lot easier, okay. So, this is what's happening: the tension in the rope right here is being redirected by this pulley because that's what pulleys do—they redirect force. But down here with the snatch block, we're doing the same thing; we're redirecting the force. But you have tension in the rope and tension in the rope. So all you do is you put tension in a rope somewhere, and then you add up as many ropes as possible on the thing, and that's how you get mechanical advantage.

So in this case, how much force is on the cinder blocks, do you know? - Two. - Two times the tension. I don't know about you, but I understand things a lot better if you can work with it with my hands. So I 3D printed a bunch of pulleys and snatch blocks, and we're gonna rig these things up and generate a model of how we were picking up those cinder blocks. When I pull on this rope, that tension transmits itself all the way through the rope to the very end. Wherever the rope is, there's also tension. If I pull here, think about the word pulley; it pulls on the rope on the other side of the pulley right there.

That pulls on the rope there at the bottom, which then pulls on the rope on the other side of that pulley, which ultimately pulls against that hook at the very end. All of the ropes are in tension. Now, if you look down there at the cinder block, you’ll notice that there are two arrows pulling up on that pulley. That's why we get twice the force on the cinder blocks. But what if we wanna pull harder? Can we just add more ropes and tension? Yes, we can using this. It's basically a double pulley. Some people call this a block and tackle. Instead of two ropes pulling down here, we get four.

Just a little bit of force here, even with my pinky finger, that's like 10 pounds of force by just barely pulling at all. This is the same number of ropes and pulleys and everything; it's just flattened out so we can see what's going on. So, I've got a scale. I'm gonna attach a scale to the input of the rope, and remember, if we put input tension, that tension goes all the way through. So as I pull here, I have one, two, three, four ropes connected to the thing we're pulling. So if I put two pounds here, look at that; I get eight pounds on the output. That's awesome! I'm getting four times the force, but I'm only moving it 1/4th as far.

How far do you think we can go with this? You think we can double it again? So now we have two blocks with four pulleys each, which if you count all those up—one, two, three, four, five, six, seven, eight—we have eight ropes in tension on that block. So as I pull here, look at this; that's nuts. That is a little bit of force, and a lot of output. That is some serious mechanical advantage. Look at this though; the ropes over close to me are moving a lot, but the ones over near you aren't moving as much.

Let's break this thing apart again and see if we can understand what's happening. This is so awesome! (board clunks) Oh man, that's a great shot! Okay, so here's what we got: we've got one input pulley; let's count up the tension again; one, two, three, four, five, six, seven, eight. I put two pounds here on the input. Oh, that is a lot of force on the output. Do you remember on the block and tackle, the ropes we're moving at different rates? Well, think about this. On this side over here, that rope is tied up there. It's not going to move. On this side, I'm pulling the rope. It has to move as much as I pull it, and the same is true for this one because it's just redirecting that string.

But after that, everything is affected by how much this moves. So, just playing around with it here, you can see that these ropes move a whole lot more than that one over there that doesn't move at all. There's a lot going on here. Not this is the sort of thing that, yes, you can probably explain it with words, but if you have a fundamental understanding of how this stuff works, and you just know how to use it to your advantage, you can get yourself out of some really interesting situations.

For example, the other day, the driveshaft broke on my buddy, Jeremy's truck, and we had to figure out how to get his truck up onto a flatbed trailer without a winch. Snatch block! We rigged up a pulley system so that we could pull his entire truck up onto the trailer using only ratchet straps. We figured it out, but because we were trading force for distance, it was taking forever. That's when a nice guy named Jeff showed up. He drove up, offered to help, and instantly understood our pulley system and knew what to do with this truck.

We disconnected one of the ratchets, put Jeff's truck in its place, and pulled this truck up until the rope hit the trailer. One thing I love about Alabama is nice people like Jeff just stop and help you, and they instantly know what's going on. For example, watch how quickly Jeff figures out all the mechanics once I tell him we have an extra snatch block. (engine idling) Oh, I'm so excited; we're gonna do a double snatch block! Oh, this is great! I'm gonna put that one— - It's locking on the block? - Yeah, yeah. - Okay. - If you'll point that direction. - Yeah, I'll do it.

I'm gonna level with you; Jeff is the kind of guy I wanna be when I grow up. Watch how he just picks up a snatch block and starts working. He just knows what to do. Also, his hands are just amazing. Watch this man work. (engine idling) Snatch block engaged. (Jeff chuckles) How many snatch blocks you got? - [Jeff] About five. - Dude, I'm an amateur; I only got two. (Jeff laughs) - [Jeff] I got a triple. - You got a triple? Like a— - A wooden triple block. - A block and tackle? - Yeah, that'll work. (chains clang)

Oh, dude, that's a thing of beauty, my friend! Any day you can use a snatch block is a good day. So yeah, snatch blocks can get you out of a hairy situation; knowing how to use them can help you make friends, thank you so much dude, and they can also be a ton of fun. Zip lines are basically just snatch blocks. You have the ability to break apart the pulley, and you can insert a cable into it without having to disconnect the cable from either end. That's essentially the definition of a snatch block: a pulley where you can insert a line without having to take apart your line from whatever it's hooked to.

Snatch blocks are amazing, and where else can you get amazing views of the rainforest canopy like this without having a snatch block? (fast forward zip lining) (pulley clanging) Muy bien. - Amigo. (metal clanging) Can you hold this, then? - Si. That's awesome! (girl chuckles) (Jeep engine roars) (grasses rustling) Okay, so you can do a video about snatch blocks without getting a Jeep stuck; so let's go do that.

Let's say you got the Jeep stuck. You might be tempted to find the nearest tree, pull the winch out, and pull the cable directly to that tree. What do you think, Jeremy, winch is the way to go? - Winch is the way; well, a snatch block is the way to go. (men laugh heartily) - Good answer, good answer! If we pull that winch out directly to that tree, we would only be able to pull the Jeep with the force that that winch is able to apply. Snatch block! We're gonna snatch block this bad boy out of here! What you actually wanna do is put the snatch block on the tree side, then take that hook, and you hook it back to the Jeep, and so you have twice the pulling force with your snatch block.

Alright, you got the winch, right? (engine idling) - I got the winch. - Okay, here we go. Cut the engine off and put it in gear, and just see if it'll pull the Jeep. - [Jeremy] And like drag it, okay? - Yeah, see if it'll just pull it. - Ready? - Yeah. (cable motor running) Oh, that's scary. That's a lot of force, dude. - [Jeremy] Yeah, man. (cable motor running) - That's good. Dude, that's a lot of force, man. - [Jeremy] Yeah, man! - Thoughts? - Alright, man. Snatch blocks are awesome, man. (men laugh)

There's a type of pulley system we haven't talked about yet; it's a compound pulley system. You remember the block and tackle? We had an eight-to-one mechanical advantage? Well, this has the same mechanical advantage, but it does it a different way. You remember we add up the tension on these ropes, and we have one plus one is equal to two? But if we have two plus two, it's equal to four, and four plus four is equal to eight; we can come up with an eight-to-one mechanical advantage just like that with fewer pulleys. This is fascinating, and one of the first people to come up with this concept is a guy named Archimedes.

To learn more about Archimedes, I went to my local library and got a book by a man named Plutarch, who mentions an interaction between Archimedes and King Hiero of Syracuse. It's a really interesting story, but it's gonna be even better if I tell it to you with this flannel board. So it goes like this: Archimedes writes a letter to King Hiero of Syracuse, and he's like, "Yo, King Hiero, I'm really good with pulleys and stuff." And Hiero's like, "Why don't you prove it?" And Archimedes is like, "Well, I will if you give me a warship." And King Hiero's like, "Yo, dog, here's your warship."

And Archimedes is like, "Yo, dog, I hear that you like pulleys. I got pulleys on pulleys on pulleys." And Archimedes does something amazing. Under his own physical strength, he pulls an entire warship out of the dock, which totally impresses the king because that's what happens when you know how to use pulleys; you impress people. So people have been using pulleys and snatch blocks for thousands of years, and they've been impressed all the way back in the day with Archimedes. But they're gonna be used for thousands more. That's why you need to know how to use a snatch block.

Don't take my word for it though; I'll let Veteran Astronaut Commander Chris Hadfield explain it from his point of view. - The biggest difference between being on Earth and being in space is that you're weightless, and when you're floating around weightless, like on the Space Shuttle, it's really hard to get leverage. You can't dig your feet in; you can't use the weight of things to hold 'em in place. So having a way to hook on one end and hook on the other end and apply a steadily increasing force is really important. And that's why on board the Space Shuttle, we have snatch blocks. They're part of normal equipment. In fact, there's a special stowage block for them that contains a couple, and they get used pretty regularly, both inside the ship and even outside on a spacewalk.

You're in a problem; you have a load; you have to pick it up; what do you do? Snatch block! (metal clanging) (Destin laughs) (girl laughs) It's kind of funnier when it doesn't work, isn't it? Snatch block! (metal clanging) Snatch block! That is exactly what you want. You wanna be the person that knows how to use the snatch block, understands mechanical advantage, and gets your team out of the situation. (speeding traffic) There's a road crew on the side of the road repairing the guardrail with a snatch block. (speeding traffic) Thanks, man. - Yeah, man. - Have a good one. - [Crew Man] You, too. - (chuckles) It was kind of weird; I pulled over and said, "Hey, can I check out your snatch block?" (laughs) And they were like, "What are you talking about?" (laughs) Pretty cool, though. (speeding traffic) I should get back in my truck.