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  • 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? 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?

  • Make it horizontal - hold it, hold it, hold it.

  • Come on. Just try to - I want you to hold it out horizontal. See if you can. Hold it,

  • hold it! Ahh, come on!

  • No. 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. Five, four, three, two, one. Boom.

  • 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.

  • agggh I mean it's just kind of awkward with the

  • hand. Careful!

  • Ah, che Careful!

  • Ha Oooohhh

  • 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, nine, eight, seven, six, five, four,

  • three, two, one.

  • Pull! Go.

  • 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.

  • Ready? Here we go: three, two, one.

  • Beautiful!

  • Let's go again in three, two, one.

  • Nice! Smooth.

  • Three, two, one.

  • It feels incredibly, incredibly light as I do that.

  • When you said it felt incredibly light, yeah

  • you mean when you're lifting it feels light? Yeah.

  • It shouldn't! I know.

  • Hahahaha Honestly, I have lifted it up with one hand

  • when it's not spinning. Yeah.

  • And it feels really hard to lift it up, like it's a big effort.

  • Yeah. But with this, when it's spinning it honestly

  • felt like it was just... wanting to go up by itself.

  • Yes. 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 72 kilograms. 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's about 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, four, three, two, one.

I am here at the University of Sydney where the mechanical engineering shop has built

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A2 初級

反重力輪? (Anti-Gravity Wheel?)

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    蒼蒼 發佈於 2021 年 01 月 14 日
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