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 pulley 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 an 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 flat bed 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 it's 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 the 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!

Is 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.

- [Destin] 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.

- [Destin] Dude, I'm a amateur, I only got two.

(Jeff laughs)

- [Jeff] I got a triple.

- [Destin] You got a triple?

Like a-- - A wooden triple block.

- [Destin] 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?