Nut will not stay on the bolt.

[MaxHeadRoom]

Picked one up to amuse the Grand-Kids.
https://www.youtube.com/watch?v=Q10KmQ3p4Co

(Courtesy of Michael Faraday).
Max.

[Dave C]

My grand nephew would get a kick out of that.

[A.K. Boomer]

pretty intricate little devise and unless it functions off of eddy currents im not getting how the brass nut is being manipulated.

[MaxHeadRoom]

pretty intricate little devise and unless it functions off of eddy currents im not getting how the brass nut is being manipulated.

Look up Homopolar motor You can make one with a battery and a drywall screw.
Very first motor by Faraday.
Max.

[michigan doug]

I suspect the magnet on the thumb acts as a switch, and then it has something to do with the right hand rule...

Very clever.

Or, perhaps the magnet is just to supply a magnetic field...

[A.K. Boomer]

Look up Homopolar motor You can make one with a battery and a drywall screw.
Very first motor by Faraday.
Max.

still does not explain it does it ? there's no direct current going through the nut - I think somethings spinning inside and then the eddy currents are rotating the nut no?

[PStechPaul]

I think there is an insulated conductive wire or shaft inside the bolt that provides a current path in the reverse direction through the surrounding metal. It creates torque on the bolt and the nut, but the bolt is held and the nut is free to spin.

[Mike Amick]

One of the commenters said it was pretty noisey ... if that's a clue.

[A.K. Boomer]

That speaks of a crude internal motor homopolar or not, and the nut is getting dragged along for the ride with eddy currents.

I can see the kids being a little less impressed when they have to ask granpa the question "how come it sounds like grandma's electric can opener ? "

[Jaakko Fagerlund]

still does not explain it does it ? there's no direct current going through the nut - I think somethings spinning inside and then the eddy currents are rotating the nut no?

Explains it fully, as the video shows everything needed for a homopolar motor.

Best of course is to buy that thing, it costs 4 EUR per bolt.

[A.K. Boomer]

Explains it fully, as the video shows everything needed for a homopolar motor.

Best of course is to buy that thing, it costs 4 EUR per bolt.

I think your missing my point - and yes I believe esp. with someone making the comment that it's "noisy" that there is an internal motor inside that's rotating, but the nut spinning off is just a by-product of that fact - and it's doing it because it's getting caught up in the eddy currents from what's going on internally, an aluminum nut would behave the same way - although non-magnetic they are still influenced my magnetism...

aluminum probably not the best choice due to creating more friction...

[J Tiers]

Explains it fully, as the video shows everything needed for a homopolar motor.
.....

Not quite.....

The rotating part of a homopolar motor has a current through it, RADIALLY, with an axial magnetic field . That nut has NO radial current in it, so it is not the same thing. and that magnet does not set up an axial field. Look up the homopolar motor and see.

In fact, it is hard to see how any current will flow in the nut, since one would expect the brass bolt to carry the majority of the current, the thin nut would not get much if any.

it may be that the principle is similar, but if so, the actual homopolar rotor does not seem to involve the nit, which rotates evenly despite its distance from the small magnet. presumably there is something else inside.

[PStechPaul]

From the Wiki article, here is a diagram showing current, magnetic field, and forces for a simple homopolar motor made from a dry cell, magnet, and two loops of wire:


By Ths1104 and Smial - File:Motor_homopolar_flux_force.png (File version without logo), Public Domain, https://commons.wikimedia.org/w/inde...curid=24882076

So there must be a conductor on the axis of the bolt which conducts current opposite in direction to that through the hollow cylindrical walls of the bolt. The video shows the magnet placed on the side of the bolt, rather than on the end as shown in the diagram, but it might not matter. I think there will be significant current flowing through the nut to provide torque, especially if the bore is large enough to make the walls very thin. To test that hypothesis, try coating the threads with non-conductive oil or paint.

https://upload.wikimedia.org/wikiped...1_smial_wp.ogv

[J Tiers]

The field will weaken at the far end of the bolt, but the nut seems unaffected by distance.

The weakened field will have less torque.

[Barrington]

The comment that the device is noisy in operation suggests to me that it might simply be something vibrating the bolt cyclically and the nut is just precessing off. The most obvious candidate would be a pager motor - there are plenty of very cheap ones small enough to fit inside that size of bolt.

The magnet is then a covert means of operating a switch and nothing to do with the action whatsoever.

Cheers

.