Anti-gravity... Well Sort Of...

[Fearless]

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Fun stuff huh.

[napoleon_in_rags]

1. Wow. I dunno much physics, but I bet it has something to do with this:

http://en.wikipedia.org/wiki/Precession

[muriel_volestrangler]

4. Yes, I think you might call it precession

I'd explain it as a consideration of the angular momentum of the object. Angular momentum is a vector quantity, with the direction being the axis round which the object spins (and a convention that when looking in the direction of the vector, the object is spinning clockwise - the same as a normal screw, which goes in the positive direction when you turn it clockwise), on which you can use vector addition to work out what's going on. As he starts with the object level, pointing to the right of the stage as we see it, it has a large angular momentum in that direction - horizontal, pointing across the stage. As he turns a bit to one side, he is adding a small amount of angular momentum with a vertical direction (his axis is vertical). Add those vectors together, and you get a new angular momentum vector that is slightly above horizontal. Since he has supported only the end of the pole away from the spinning weight, this will raise the weight. And as he rotates more, the weight will rise further. As the object nears vertical, the effect goes away, and he has to let it down again.

Note that if he had turned the other way, the weight would have moved down (or if the drill had spun the weight in the opposite direction).

[napoleon_in_rags]

6. Okay, so...hypothesis.

Based on my limited physics from Kahn academy.

So the spinning wheel wants to move around like a gyroscope/top via precession, it wants to go around in a circle and he's holding it back. The energy required to move it up is lessened at an instant if its going up a "ramp"...It requires a force vector pushing it "forward" and "up" over a longer distance, not just up. The spinning top like behavior basically has it already moving in a circular direction of its own accord, so by lifting it up he gets a "ramp" like effect. The weight at an instant is only equivalent to the "up" part of the vector, the forward part of the vector is taken care of already. So he experiences the 40 lb. weight as if it weighs like 10 lbs. The rest of the energy comes from the momentum in the spinning wheel. If my theory is correct, the wheel must be spinning more slowly after each time he does it.

This would be a fun one to test at home, although I've heard fly wheels can be dangerous.

[muriel_volestrangler]

7. I'm not good enough to be able to explain all this

But, if you've got up to an hour free, you may enjoy Prof Laithwaite's Royal Institution Christmas Lecture for this (a long standing tradition of a series of lecture for children about science, broadcast since the 1960s by the BBC). 7 parts; the gyroscopes start in part 2:

part 1:

part 2:

at about 2 minutes 40 seconds

[napoleon_in_rags]

9. thx. nt

[progressoid]

12. Oh, that brings back memories.

I used to love playing with my cheap little gyroscope when I was a kid.

[muriel_volestrangler]

8. One thing I will say - I think the weight will remain 40lbs

What is different when holding the gyroscope is that you don't have to exert a torque on the end of the handle. If the weight isn't spinning, and you have both hands at the other end of the shaft, separated by, say, 10cm, and the shaft is 100cm long, then the torque of the (say) 15kg wheel at about 100cm has to be balanced by a force of 150kg in one of your hands - which is what makes you drop it. If you grasp the shaft right by the wheel it will be, of course, much easier to hold - hold it at the centre of mass of the whole object, and only the 15kg force is needed. When spinning, the mechanics of how the object is rotating (or apparently trying to rotate) around its centre of mass, or another point, are very different, and effectively you don't have to worry about the leverage of the wheel being at the far end of the shaft to stop it dropping.

[napoleon_in_rags]

10. for sure.

It weighs 40 pounds at all times, but question is how much force does it take to raise 40 lbs above your head, or two feet. I understand the torgue thing, but it would be tough to lift a 40 lb dumbell the same way. He does it like its 15 lbs. I think there is a trick where the momentum is helping him lift.

[denbot]

2. Umm, Lagrangian.. Hamiltonian mechanics?

Head hurt, lie down now.

[Demo_Chris]

3. wtf?

[tridim]

5. Yes, gyroscopes are nifty.

[Igel]

11. Colllege physics prof told of a practical joke.

Apocryphal perhaps, or perhaps legendary.

A gyro wheel was mounted in a suitcase at an angle. The wheel was spun up and the suitcase left sitting for the victim of the prank. The intended victim was some big-name physicist (not a big name to me at the time, name forgotten before I knew the names of the Big Names).

The guy was asked to pick up the suitcase and carry it out the door and then turn down the hall. Straight out the door wasn't a problem. Turning down the hall made it fly up and almost out of his hands.