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Magnetic Ball Bearing "Mystery"

patnray

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I was wondering why no one has been discussing the experiments with magnetic ball bearings and copper tubing Randi has mentioned in the commentaries.

I think I know why the ball's motion is periodically retarded when moving south down an incline, but not when moving north. Remember, the steel ball bearing is a conductor...
 
patnray said:
I was wondering why no one has been discussing the experiments with magnetic ball bearings and copper tubing Randi has mentioned in the commentaries.

I think I know why the balls motion is periodically retarded when moving south down an incline, but not when moving north. Remember, the steel ball bearing is a conductor...
Click to expand...

For the the dumb, lazy and uninformed of us: provide a link.
 
For those of you who dont' have highly magnetized ball bearings, you can get a set of small neodymium magnets pretty cheaply on ebay.

It's recommended to superglue them together in a stack, with the fields of adjacent magnets opposing. (This is more difficult than it sounds).

The resulting cylinder can be dropped into an ordinary copper pipe for the effect.
 
I suspect the north/south effect Randi mentions requires that the magnet roll with the rotational axis perpendicular to the axis of the magnetic poles, i.e. "end over end" with respect to the poles. If so, then cylindrical magnets will not produce the effect...

Also, Randi states that he has given enough information to solve the puzzle without experimentation, and I believe that is true. Of course, experimentation would be useful to prove an explanation is correct or to choose between competing plausible explanations...
 
phildonnia said:
For those of you who dont' have highly magnetized ball bearings, you can get a set of small neodymium magnets pretty cheaply on ebay.

It's recommended to superglue them together in a stack, with the fields of adjacent magnets opposing. (This is more difficult than it sounds).

The resulting cylinder can be dropped into an ordinary copper pipe for the effect.
Click to expand...

More fun with magnets
 
Thanks, SkepticJ. Interesting site.
This demo is well known. However, thin-walled copper pipe is usually employed, and the magnet usually must be a slip-fit on the tube (like a piston within a cylinder.) With a slip-fit magnet you can't see anything but darkness within the pipe. So use wide, thick-walled pipe. Now drop the magnet again, but LOOK INTO THE TOP END OF THE PIPE. The neodymium disk will be hovering in space as it falls, repelling from the walls as well as being slowed by electromagnetic braking. If you tilt the pipe a bit, the disk magnet will slowly tumble end over end as it floats downwards without touching the sides.
Click to expand...

Seems to confirm my belief that the ball rolls down the incline with the poles tumbling end over end..
 
I was just listening to the BBC. Several physicists were discussing how the Higgs field slows moving particles by "lending them mass". It all sounded reminiscent of the old "Aether". And here we have a magnet being slowed by electromagnetic force carriers. I'm on the verge of a paradigm shift.

Time for a lie down in a dark room, with a cup of Kenya and an undemanding novel.
 
Another clue to the puzzle (from the Fun With Magnets site):
If you suspend an NIB magnet from a thread, it will promptly start swinging in its attempt to aim north. A long stack of NIB disk magnets exhibits even stronger north-south alignment forces. Since the earth's field is not parallel to the ground in most locations, expect your magnet stack to both tilt at an angle and swerve into a n/s orientation.
Click to expand...

Any guesses as to the inclination angle of the earth's field at Ft. Lauderdale Florida?
 
Ok so what will happen if you have magnet shaped like a cylinder with a hole in the middle that fits around the outer surface of the conductor (copper tube). Will it slide down the tube without touching the surface?
 
kedo1981 said:
Ok so what will happen if you have magnet shaped like a cylinder with a hole in the middle that fits around the outer surface of the conductor (copper tube). Will it slide down the tube without touching the surface?
Click to expand...

This is described on the site SkepticJ mentioned. Bonus magic: If the central tube is made of insulated copper wires, the ring magnet will fall normally.
 
I thought that what they described on the Fun With Magnets site was a copper ring with the magnetic cylinder in the center. But you are correct, with a copper tube (or even a solid copper rod) in the center you can still have eddy currents circulating around the tube (in a plane perpendicular to the magnetic field) and creating a breaking effect. And replacing the tube with a bundle of insulated wires should disrupt the creation of the eddy currents.

So yes, it will slide down the tube without touching the surface (if the magnets are strong enough and the copper thick enough).

But does anyone have a theory for the effect Randi mentions when the magnetic spheres are rolling south on a 30 degree incline?
 
All I can think of is that it has something to do with the Earth's magnetic field. However this is pretty weak, so I'm not sure it would have any major effect. I know the earth's magnetic field is complicated, but I would expect that field in in FL to be directed south as it rises out of the ground.
 
The effect that Randi describes IS a small effect added to the stronger effect of the induced fields between the copper channel and the magnetic spheres. If I remember correctly, the strength of the earth's field at the surface in North America is about 0.6 Gauss. Furthermore, since the ball is rolling down an incline, the gravitational acceleration is reduced compared to falling straight down, which makes the effect easier to see.

At the earth's north and south magnetic poles the field lines point straight up and down. At the equator they are parallel with the surface. Florida is in the northern hemisphere, thus the field is inclined toward the north. If the magnetic poles and the rotational poles were perfectly aligned then the inclination of the field would match your latitude (about 26 degrees north at Ft Lauderdale).

The effect is not noticed when the ball rolls north. It is not noticed, but for a different reason, when the ball rolls east or west. The effect is only apparent when the ball rolls south. For the moment ignore the east/west direction. Think about the relation between the ball's path and the earth's field when rolling north at an inclination that matches the inclination of the earth's field. Now rotate the apparatus 180 degrees so the south end is down and picture the relation between the path and the earth's field...
 
OK. Here's my theory. You are welcome to pick it apart and tell me where I am wrong:

With the north end down and approximately 30 degrees inclination the tube is aligned with the earth's magnetic field (probably closer to 26 deg in Ft Lauderdale and 37 deg here in San Jose). With the north end down, the steel ball bearing (a conductor) is traveling along (parallel with) the earth's field lines. Since the ball is not moving across field lines there are no induced fields between the ball and the earth's field. With the south end down, but at the same inclination, the conductive ball moves across the earth's field lines. Thus there will be an induced field, which acts to retard the motion. Since the direction of this field is dependant only on the orientation of the earth’s field and the direction of the ball, its direction is constant. I suspect that the induced field between the ball and the tubing aligns the ball so that it rolls with the poles going end over end. Thus as the ball rolls its magnetic field alternately opposes and adds to the induced field due to the earth and the ball speeds up and slows down. Since the ball spends more time on the slow side of each revolution, the average speed is decreased. East/west alignments will also create an induced field. This field is apparently at right angles to the ball’s motion, or in a fixed alignment with the ball's poles, so there is no periodic speeding up and slowing down as the ball rolls east or west.

That's my theroy, and I'm sticking to it. Unless someone can point out a fatal flaw or present a better theory....
 
In this week's commentary (11/19 Here ) Randi asks why the breaking effect is not seen when using steel tubing.

I believe I know why. The falling magnet does not directly create an opposing magnetic field in the copper tubing. The magnet creates eddy currents of electrons that circle around the tubing. The magnetic field created by these currents cause the breaking effect. It requires material that is an excellent conductor, such as aluminum or copper. Since steel is not as good a conductor, the effect is much weaker with steel tubing. This fact is put to use in coin acceptors for some vending machines. Coins roll down a ramp and pass between the poles of a magnet. Coins that are excellent conductors (silver, copper, copper clad) are slowed down and roll gently off the end of the ramp into a sorting mechanism. Slugs (and nickels) are not slowed and roll off the ramp fast enough to fall into a different bin.

So, steel tubing does not work because it is not a good enough conductor of electricity. That's my theory and I'm sticking to it...
 
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