I am here at the University
of Sydney where the mechanical engineering shop has built
this incredible piece of apparatus for me.
It is a forty pound,
that is nineteen kilogram flywheel on the end of a meter long shaft.
Can you imagine trying to hold this out horizontally
with just one hand at this end?
事实上 …几乎是不可能的 对吧？
It is virtually… it is impossible, ok?
No I’m going to let go.
You going to be able to hold this at all?
I hope so.
Can you lift it out?
放平了——抓住 抓住 抓住
Make it horizontal – hold it, hold it, holdit.
Just try to – I want you to hold it out horizontal.
See if you can.
Hold it, hold it! Ahh,
What I’m going to do is I am going
to spin this up to a few thousand RPM and then I’m
going to attempt just that,
to hold it from one end and have it out horizontally.
5 4 3 2 1
five, four, three, two, one.
I’m going to let go with my left hand.
What you’ll see is that the shaft remains horizontal,
see it going around there.
It almost looks as though the wheel is weightless.
How does this work?
Well instead of pulling the wheel down to the ground
as you’d expect, the weight of
the wheel creates a torque which pushes it around in a circle.
You may recognise this as gyroscopic precession.
For a more detailed explanation, click the annotation,
or the link in the description
to see my video on the topic.
Here I want to try something more extreme.
I’m going to try to lift it
over my head with one hand while it’s spinning.
Wish me luck.
But before I make the attempt,
Rod wisely suggests that I first check if I can lift
the wheel above my head without it spinning. OK,
let’s prove that I could lift it,
just this end, without it spinning.
Here we go.
aggghI mean it’s just kind of awkward with the hand.
HaOooohhh Just barely.
Oh goodness, do you even lift?
Clearly I do not.
Undaunted by my lack of strength, I’m going for it,
but I want to make sure the wheel
is spinning as fast as possible to give me the best chance of success.
Give it ten more seconds. Ten,
10 9 8 7 6 5 4 3 2 1
nine, eight, seven, six, five, four,three, two, one.
That was perfect.
Now I’m going to release my left
hand and holding only with my right hand at the end
of the shaft, I’ll try to lift it up over my head.
This is a forty pound, nineteen kilogram flywheel.
开始：3 2 1
Here we go: three, two, one.
再来一次3 2 1
Let’s go again in three, two, one.
很流畅 3 2 1
Smooth. Three, two, one.
It feels incredibly, incredibly light as Ido that.
When you said it felt incredibly light,yeah
you mean when you’re lifting it feels light?
– It shouldn’t! – I know. [Hahahaha]
Honestly, I have lifted it up
with one hand when it’s not spinning.
And it feels really hard to lift it up,
like it’s a big effort.
But with this, when it’s spinning it honestly felt
like it was just…
wanting to go up by itself.
It felt like I was not struggling
like I was not putting in the amount of force that you’d
think to lift that kind of weight.
I bet if you let it go,
it’d crash down to the ground.
It’s not weightless!
We can’t do that though.
We can’t do that part of the experiment.
What we could maybe do is I could stand
on a scale and we could see what the weight of
me plus that apparatus does,
while I’m lifting it up over my head, see if I get lighter in essence.
You can see that just my weight is about 72kilograms.
Now when I pick up the flywheel it goes up to
about 91 kilograms, which makes sense because
the flywheel itself is about 19 kilos, that’sabout 42 pounds.
Now we’re going to spin it
up and I want you to make a prediction.
As I’m lifting it over my head,
do you think the scale reading will be more, less than,
or equal to 91 kilograms.
What do you think?
You can make your prediction by clicking on one of the on-screen annotations or if you’re
on mobile you can click a link in the description. Five,
5 4 3 2 1
four, three, two, one.