[Captions by Y Translator] A Newton's Cradle is a well-known apparatus
that demonstrates Newton's Third Law of Motion.
That for every action, there's an equal and opposite reaction.
Today, we're going to be building a scaled-up Newton's Cradle
using billiard balls.
You've probably seen and played with those little desktop toys
made of like five silver marbles that just swing back and forth
and they make pleasant clacking noises.
They're used for stress relief or just the background noise.
Today, we're going to be building a larger one of those,
and instead of those small metal balls.
We're going to be using billiard balls.
Here's the building plan.
We'll have two frame pieces attached to the base and to each other.
Near the top, we'll have some hooks that we can run our lines through
along with some pegs that will help us make adjustments.
To start, we're going to build two pieces of frame.
And each one is going to be made of three pieces of our 2 by 2.
Each of those pieces is going to be 18 inches long to start.
So let's get cutting.
One of these beams will be the top piece,
and then we're going to have two legs
coming down on the sides of it.
So it'll basically be like that.
And what angle we have this setup is pretty subjective.
It can be kind of whatever you want.
So I'm just going to take one measurement
and then cut all of the pieces to match.
Beautiful.
I just need to trim the bottoms
so that it will sit flush on the board.
We've got all our pieces cut.
Now, we're going to secure them together.
We'll make 2 of this shape.
Excellent.
Each of our billiard balls is pretty much
exactly 2 and 1/4 inches in diameter.
So what we need to do now is drill
some holes into the top of each support beam.
Five of them, because we're going to have five different billiard balls,
and of course each hole needs to be two and a quarter inches apart.
These four dots and this one cross point, is where we will
drill the holes to attach our hooks.
Let's do the same thing on the other side.
These holes we just drilled
are going to have these eye hooks in them.
However, when you're making a Newton's Cradle,
it's actually quite important that all of the balls
in the Cradle line up perfectly in all three dimensions.
They can't be too far apart from each other,
they can't have the strings leaning toward each other
so that there's too much pressure holding them together
and that can be a really tricky thing to do.
However, the system I have devised
seems to work pretty well for being
able to adjust where they hang.
So we're going to have these five hooks.
But we're also going to have five sort of tuning pegs
that will let us adjust how the billiard balls hang.
We're just going to be using some pieces of dowel
as the little tuning pegs.
We'll have the hook a little bit higher.
The line will come from the billiard ball up through the hook,
and then back down to the peg
which we'll install a little below the pegs.
So that way, all of the pressure should always be on the hook
regardless of where on the swing angle the ball is.
Now we want these to be sturdy
as they sit about eight inches apart.
So what we're going to do is take some of our scrap pieces of 2 by 2,
cut a couple of lengths that are 8 inches long
and attach them on to the four corners.
I think this needs to be black.
We're gonna turn this black.
To attach the billiard balls onto the frame,
we're going to be using these even
smaller little eye hooks and some fishing line.
And to get these little eye hooks attached to the billiard balls,
we're going to use a very small drill bit.
We'll drill two holes into each billiard ball
and then screw the hooks in
and then attach the wires onto those.
We've got all of the hooks installed onto the billiard balls.
And now what we need to do is attach the cords.
And for that, we're using some thin fishing line.
The knot that I'm using is called the palomar knot.
And it's designed for attaching fish hooks to the line.
You start out by just making a loop on one side.
With, I've got plenty of extra here.
If you're actually doing this on a hook,
you wouldn't need nearly that much extra.
But you will on this you'll see why.
So that loop pushes down through to eye.
And we've got these two sides.
That's where the end of the doubled over portion is.
And we're just going to tie this in an overhand knot.
Overhand knot right there.
And what we need to make sure is that the loop on this side
of the overhand knot is big enough they can fit all the way
around the billiard ball.
And then we pull it tight.
And we can cut off all the extra.
It gets a little bit more complicated
when you attach the second one
because you still have to fit it all the way around the billiard ball.
But you don't want to catch the first line in you're knot.
And so you have to sort of feed it through.
So, I'm going to take this loop,
wrap it all the way around the billiard ball.
Then I also have to just pull that out of the way
before I tighten this one down.
This is going to be part of our base.
It's going to go on top of this other piece of plywood.
And that just is going to give us a nice look to it.
Let's go trim this down.
Now we need 10 pegs to fit in these holes.
Each one just about inch and a half.
Maybe two inches long.
Make it an even two.
So that we can attach our fishing line to these sort of tuning pegs,
we're just going to drill a hole through each of them.
Now we've got all of our frame built and it's time to start
attaching the billiard balls.
Not doing anything too fancy here.
Just a knot on one side
and then a square knot on the other side.
Now by twisting that peg,
I can shorten or lengthen the line on that side.
And that moves the ball hanging down below.
Beautiful.
Four more.
It's not going to be perfect but fortunately we have
the ability to adjust and get it closer.
At this point, I think we are ready to test it out.
It seems properly calibrated.
Let's see how well it works.
The Newton's Cradle is wonderful for demonstrating
Newton's third law of motion
which is that for every action,
there's an equal and opposite reaction.
Billiard balls are not very compressible and so all the energy
that enters into one side of them tries to exit out
the other side if it can't move.
If I pull back on the red ball,
the orange yellow and green balls
for the most part stay in place.
And in the energy from the red ball,
is transferred over to the blue.
The blue swings out,
swings back and transfers its energy
back through the middle three
and into the red ball again.
This is not a perfect system.
And in fact, there's no such thing as a perfect system.
So some energy is not transferred just the way we want it.
That's why we start seeing some swinging motion
and why it doesn't continue moving forever.
Some of the motion is transferred through the lines up into the frame,
into the base,
onto the workbench,
and it's lost there.
A little bit of the energy is actually turned into heat
as the billiard balls collide with each other.
In a truly perfect system,
the three billiard balls in the middle would never move
and the two on the outsides
would keep bouncing back and forth forever.
That would also require there was no air resistance.
The little desktop toys usually use a metallic ball
which is even better at transferring energy than these billiard balls.
They're also often slightly magnetic which helps hold them together
if the energy from a swinging ball isn't pushing it out of line.
You can make some really interesting patterns by playing with this thing.
If the line is swinging and then one ball is pulled away and allowed to drop,
the line will keep swinging but the outside balls
will bounce on and off.
Random fact, the name Newton's Cradle was coined in 1967
by the English actor Simon Preble.
By shortening the strings,
we eliminate some of the play
so it should last a little bit better.
But we also have a much shorter period
which is the length of time it takes the ball
to swing from one apogee to the other.
Newton's Cradle, a fun toy to build and use.
I like to try and to figure out interesting new bounce patterns with it.
Overall, I really enjoyed building it.
And it's a good example of Newton's laws of motion and physics.
Are there other things you would like to see us build
demonstrating basic science principles?
Let us know down in the comments as always.
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