- This is a chaotic pendulum.
Its motion is unpredictable.
The arms of the pendulum have been arranged in such a way
that it's motion is what we call chaotic,
so it's very close to my face.
Chaotic means that there is no equation
that you can come up with
where you can plug in some time in the future,
and it will spit out the position
of the arms of the pendulum in a reliable way.
Another way of saying that is that this pendulum system
is sensitive to initial conditions.
What that means is if I try
and recreate the same pattern of motion twice
by setting the pendulum in the same position at the start,
I won't be able to do it
because, well, I can't get the position exactly the same.
So if I set it off like that,
there you go.
I will try and recreate that now, but I won't be able to.
And, in fact, you know,
even if I could get it in exactly the same position,
all the molecules in exactly the right state,
the air around it, I have no control over, so.
So I've overlaid the previous experiment on top of that,
and you can see the motion is completely different
the second time 'round.
So to illustrate how chaotic this system is,
I want to see if we can conduct
an experiment in the comments,
and this experiment is to do with flipping,
what I call flipping.
Flipping is when the lower arm of the pendulum
passes through the upper arm of the pendulum like that,
so it can either go in that direction,
or it can go in that direction.
And you'll have seen it does that quite a bit,
but eventually it slows down and stops.
So there is a point at which you have the last flip,
and I want you to predict when that last flip happens.
So, I'll set the pendulum off again,
and when you think the last flip has definitely happened,
there will be no more flips,
pause the video and leave a comment with the time code
of when that last flip happened,
when you think the last flip has happened.
Now there will be a tendency to cheat, please don't do that.
If you pause the video, leave a comment.
Don't kind of pause the video and think,
actually I won't leave a comment just yet.
I'll just play the video and make sure that I'm right
because then what will happen is it'll flip again,
and you'll think, oh no,
I didn't mean to pause it there anyway,
I'll just do a new one.
If you pause the video, you must leave a comment.
No exceptions, okay.
And also, you know, the video is like finite in length,
so if you pause the video one second before the end,
you'll definitely have paused it after the final flip,
but that's nothing to be proud of.
What you're trying to achieve is,
you're trying to get as close to the final flip as possible
without it being before the final flip.
So after the final flip, but as close to it as possible,
I hope that makes sense.
Okay, here we go.
Okay, the final flip has definitely happened at that point.
So there you go, the chaos pendulum.