Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Iacopo]

I agree that the rotation of Earth has not an effect with what you see.
The longer comment in AskPhysics is interesting, (but I believe the candle has no effect at all).
As you say correctly, the wheel should be magnetized axially.
But maybe there is a little amount of magnetization in the horizontal sense too, in the wheel.
Maybe, this could happen if the magnets are not perfectly aligned with the wheel, so the magnetic field in the wheel would be a bit asymmetrical.
The axis of the magnetic field would not pass through the center of the wheel but somewhere near it, and, that side of the wheel would 
acquire a polarization relatively to the opposite side of the wheel, then the wheel could react to the magnetic field of Earth.
Another possibility is that it is not the wheel that it is reacting to the magnetic field of Earth, but the magnet of the wheel that reacts to the magnet above, to which it is suspended.  For this to happen, there must be some misalignment between the magnetic fields of the two magnets, (also because of the little magnets added above, as suggested in that comment ?), and the axis of the magnetic field of the magnet of the wheel should be at least a bit tilted from the vertical, otherwise the magnet above couldn't apply any spinning force to it.
But, since you have been able to spin the wheel with a magnet near it, more probably it is the wheel that it is magnetized, horizontally.
With that magnet you could also see what is the side of the wheel that is attracted from it, and if, that side, would point consistently at the north/south, after having removed all the other magnets around.
If the magnetic field of the wheel is not stable, but changes orientation, this could be due to the magnet of the wheel not being fixed steadily, maybe it can spin/tilt a bit relatively to the wheel, and, when this happens, the magnetic field in the wheel changes orientation.     
 

[Iacopo]

Also I want to point out that with axially magnetized disc/ring magnets the magnetic field varies on the edge, at certain spots it is more powerful than at others.

I didn't know, this also could explain the asimmetry of the magnetic field in the wheel.

[Pasi]

I did some testing: first three runs ended so that the marking pointed south-west. All three landed in the same sector of maybe 20 degrees. Then I got a north-east, 180 degrees opposite. After that runs started to stop at random directions. At some point I realized I hadn't fastened the bolts appropriately, so the wheel and the spinning magnet was able to move in respect to the threaded rod. After fastening the bolts tightly, I got the following results for 10 runs: 6 pointed at north-east (all with in 30 degree sector) and 4 pointed to south-west (these again with in 30 degree sector). 10 test runs isn't much but since they all landed within a total of 60 degree sector I think it's safe to say the wheel doesn't stop at random spots.

[Iacopo]

Mmm...  that's intriguing.
It seems like there are two preferred positions at the end of the spin, instead of one.
Permaro in Reddit seems to suggest that there is only one real preferred resting point and that the opposite position is simply an unstable equilibrium point. 
I don't think so, but this should be easy to judge;
the back and forth movements could not happen around the unstable equilibrium point, so, if you always have them, you have two real preferred resting points, two points of attraction.
Why two points of attraction ?
Maybe the two little magnets you added above ?
What if you change the position of those two little magnets, would this change the position of the two preferred resting points of the wheel ?
 

[Pasi]

I have tried positioning the little magnets differently, spins still end pointing to SW and NE directions. When I turned the magnet that is spinning with the wheel 90 degrees in different position with respect of the threaded rod and the wheel I have got also runs stopping at South, and the SW and NE. One interesting thing is that with minimal initial pushes the back and forth movement seem to be way smaller - the last back and forth movement was occurring only in sector of maybe 10 degrees. On the 10 hour spin the back and forth movement was in a sector of 180 degrees. So maybe you are on to something with your eddy current, coin theory. Maybe the changing sector of the back and forth movement is just due changing magnetic pull - it needs to be constantly fine tuned to get the least amount of friction. I'll do more tests to hopefully gain a better understanding of this..

[Pasi]

what I mean by fine tuning the magnetic pull is that I constantly have to increase the opposing little magnets because of the magnetization, after another minimal initial push test ensuring, the magnetic pull was only just sufficient to carry the weight. The same happened approx sector of 10 degrees of back and forth movement, also a new stop direction north-west - I'm baffled

[Iacopo]

Since you continued to have the same two preferred resting points of the wheel, even changing the position of the static magnet above, and that of the little magnets, I would say that this seems a strong clue that the magnetism of Earth is involved.
And, if so, maybe the eddy currents are not necessary to explain this phenomenon.

It is puzzling, it seems like the wheel behaves like the needle of a compass, but with two north poles at the opposite sides of the wheel, and two south poles at 90 degrees far from the north poles, (would this be possible ??)

Maybe, if you touch the circumference of the wheel all around with the tip of a knife, you can feel which sides attract it more.
You could see in this way how many poles there are around the wheel, two, (or four !?)
 

what I mean by fine tuning the magnetic pull is that I constantly have to increase the opposing little magnets because of the magnetization, after another minimal initial push test ensuring, the magnetic pull was only just sufficient to carry the weight. The same happened approx sector of 10 degrees of back and forth movement, also a new stop direction north-west - I'm baffled

Not sure what you did mean here.

[Jeremy McCreary]

Given your latest observation of a new stopping azimuth, I think you're going to have to take a lot more observations to establish a statistically significant preferred stopping azimuth. To visualize any trends as they emerge, you might consider plotting your azimuths as they come in on a rose diagram -- basically, a radial histogram (see Wikipedia if unfamiliar).

Given that we have still have no agreed-upon physical reason to expect a preferred azimuth, this kind of care is especially warranted.

The fact that you observe narrower spreads in stopping azimuth over shorter time intervals raises the possibility of a Coriolis effect akin to that behind the Foucault pendulum. I think that's pretty unlikely given the short length of your suspension rod, but we're already grasping at straws.

Q: What is your latitude?

Foucault pendulums are notoriously sensitive to even the tiniest of lateral forces inadvertently applied to the bob at the time of release. For that reason, they're often pulled back with a very thin string. Once the system settles down again, they're released by burning through the string while under pure tension. Have you tried that?

Another hypothesis worth considering: Pesky aliens parked in high-Earth orbit polarizing the subspace tachyon field just to mess with us. I read on the Internet that they do stuff like that all the time. Heck, they might be even standing around the high-res telescope viewer laughing and elbowing each other right now. Assuming they even have elbows.

[Pasi]

Wow, I learned a new word: azimuth! When playing with the direction of the magnet that is spinning with the wheel there are irregularities on preferred resting points, but most of the runs still land with the marking pointing to SW and NE.  What Jeremy said about rose diagram and having a lot more sampling is exactly what I should do. There are too many variables, that make determining unquestionably the reason behind preferred resting points / the back and forth movement an infernally hard task. For example I constantly find tiny specs of iron between the contact points, but trickiest thing is the increasing magnetization in the setup (or at least what I think is due magnetization) The little magnets on the stationary overhead magnet are attached repelling mode. The steel casing of the big stationary magnet enables this. I started with one 4mm x Ø20mm neodymium (2,5 kg pull force) and now there are 12 of those attached repelling mode. I live in Southern Finland, latitude 60,4. Not much luck with the knife thing Iacopo suggested, maybe a compass would give better results. I still need to test it with compass, I don't own one. Hmm, The burning string, might be worth while to test.. and damn those pesky aliens, yet another possible variable to be taken into consideration. I'd still like to hear your thoughts on the small sector of back and forth movement when the initial kinetic energy (push) is small, compared to push with a lot of initial kinetic energy, the sector of back and forth movement is way bigger. Is it maybe something basic that I fail to understand?

[Iacopo]

I'd still like to hear your thoughts on the small sector of back and forth movement when the initial kinetic energy (push) is small, compared to push with a lot of initial kinetic energy, the sector of back and forth movement is way bigger. Is it maybe something basic that I fail to understand?

How much small ?  If you turn the wheel with so small initial kinetic energy that the wheel spins for, let's say, 10 degrees, before starting the back movement, I wouldn't expect a large back movement.  For the same reason, if you push a pendulum very slightly, it will oscillate very slightly.

Another little test:
If, during the back and forth movements, when the wheel has come to a temporary rest, and before to start a back movement, you intentionally stop the starting back movement holding the wheel with your fingers for a few seconds, what does it happen when you release the wheel ?  It starts the back movement, or, you killed definitely the motion and the wheel doesn't move anymore ?
The second case maybe could be a clue of presence of eddy currents, which could help the back and forth movements, until present.

[Pasi]

Sorry for being ambiguous, what I mean by "small movement test" i mean around 1 rpm. The wheel still runs maybe 10 revolutions / 20+ minutes. I will try the test ypu suggested... thank you, that was a great suggestion!

[Pasi]

Yesterday I tried to do the test you suggested, after 5 hours of spinning I forgot about the wheel and accidentally stomped the floor too hard dropping the wheel, this happened twice Today I made a new run with lesser initial push, after two hours and almost boring myself to death while staring it intensively, the spinning finally stopped. After I held the wheel stationary for couple of seconds, the wheel moved backwards 90 degrees. I tested turning the wheel to the same stopping point and the same 90 degrees of movement occurred again.

[Iacopo]

Yes, I imagine these tests take a lot of patience...
Your last test seems to make think that the wheel behaves simply like the needle of a compass, moving back and forth around the final preferred resting point, which seems driven by the magnetic field of Earth.
I made a little discovery observing your video;
the back and forth movements start at about 10^h14^m30^s.
The last full revolution is between 10^h10^m10^s and 10^h14^m30^s.
It can be seen that, during this last full revolution, the speed of the wheel is variable, it accelerates during the 180 degrees before the final resting point, and it slows down during the 180 degrees after the final resting point.
This seems to demonstrate that there are not two preferred resting points in the wheel, but only one, which, for some reason, is not stable, and, for this reason the wheel can end spinning in two different positions.
So my previous idea that there could be two north poles and two south poles around the wheel is wrong.
Otherwise there should be two accelerations and two decelerations during one revolution, but there are not.
Maybe the magnet of the wheel is not fixed steadily, maybe it can tilt/move a bit, and, when this happens, the wheel magnetization and the final resting point change. Or, as you said, "Maybe the changing sector of the back and forth movement is just due changing magnetic pull".
Unless pesky aliens in action....   

[Iacopo]

what I mean by "small movement test" i mean around 1 rpm. The wheel still runs maybe 10 revolutions / 20+ minutes.

That's different... and... quite puzzling to me.
At parity of magnetic pull, I would expect a similar amplitude of back and forth movements in different spins, indipendently from the starting speed of the wheel. 
More friction between the contact points could cause a more rapid slowing down and so also littler angles of back and forth movements.
Are you sure that you had not a higher magnetic pull, when observing reduced angles of back and forth motion ?

Another question:  do you always have back and forth movements, at the end of the spin, both in north-east and south-west ending positions ?
 

[Pasi]

You pretty much summarized my thoughts. I too have noticed this accelaration and decelaration, ok only one per a revolution - I wasn't sure.

I previously wondered whether there could be a correlation between the initial kinetic energy and the sector of back and forth movement. This is probably not the case. I'd say the magnitude of back and forth movement's sector is mainly determined by the difference in friction, caused by magnetization. A large sector of back and forth movement just requires a really delegate fine tuning of the magnetic pull.   

The wheel magnet is only attached by magnetism, it can be rotated by hand but during the runs it is spinning with the wheel.

I don't think the reason behind back and forth movement could be purely off balance, because the wheel and its axle, the threaded rod + contact point are secured tightly together. Sure, off balance is causing more friction but it shouldn't cause any back movement after the wheel has come to stop.. ruggedness of contact points could be one possible explanation, but the back and forth movement has been present always in these kinds of experiments. I have been mainly using pinballs as contact points, they are fairly smooth and I don't so think ruggedness can be the reason. In my diamagnetic suspension levitation experiments, magnets have always done the back and forth movement once spinning has stop.

To prove unquestionably the reason behind the movement would require more rigorous testing. I'm sure my tests have included a lot of flaws.