Levitation using permanent magnets.

Introduction.

Science consists of a bundle of theories that have not yet been generally proven wrong. Take Earnshaw's theorem for example, it states that it is impossible to levitate an object using only permanent magnets. That is like saying we cannot make an electro-magnet to pick up copper, which of course we can. I guess whether he was right or wrong depends upon how carefully he worded his theorem and I will leave that up to you to decide.

Earnshaw's argument was that using the fields from permanent magnets always produced a small unbalance and that the mass always tended to move in that unwanted direction, with an avalanche effect. I got interested in his theory over a pint of real ale with my mate Donald and wondered  ... despite what Earnshaw said .... how many magnets would be required to levitate a pint glass of beer ?. At the time I thought 15 ... how about you ?. Of course if Earnshaw was correct then no amount of magnets could do the trick, but it really depends on how he worded his theorem. 

Tops and toppling.

Most grown up kids know that spinning tops and gyroscopes work according to their own laws and can do some seemingly impossible things. For example a top spins on its point. In a way, a gyroscope does exactly the same. The reason why neither topple is because spinning gives them 'rigidity' and causes them to avoid the kind of movements that are involved in toppling. Within certain limits, the faster they spin the more 'rigid' they become. 

Ok back to our magnets. Moving two opposing magnets together results in the free one spinning around to change like poles to unlike poles and then the two magnets snap together. This is the problem in trying to levitate an object using only permanent magnets ... it looks for a slight imbalance in opposing fields and this causes a small movement ... which increases the imbalance and we get a runaway condition resulting in the snapping together of the magnets.  Now most people come up with the idea of creating a magnetic cup ... for the opposing magnet to sit in, so that it centralizes in the field of the cup shaped field and cannot wander out of it. Obviously the opposing magnets axis must be firmly fixed to prevent it flipping over ... and if you think about it we only have gravity to stop that happening.  Theoretically we would need a minimum of three such magnetic cups and the levitating part would consist of a rigid frame with three legs containing the opposing magnets ... that sit in the magnetic cups. Of course the frame would need to weigh enough to stop any imbalance in the system flipping the levitating magnet frame. For the real ale addicts I would say that the pint of beer sits on this levitating frame. Once you get it working you are guaranteed free beer for life in any pub ... whilst demonstrating it !. Mind you, if you think that your audience would pay to see 'anything' levitated, then there are smaller and simpler ways of coaxing the money out of them !.

The Levitron. 

The Levitron is a scientific style toy, that will actually cause a spinning magnet to levitate. As Rod Stewart is reputed to have once said ... "Picture wurf a farsend words, innit?". 

In the black plastic base is a fairly powerful ring magnet, which produces a vertical axis magnetic field. In the spinning top is another smaller ring magnet orientated to produce a field with like poles. So the two magnets 'want' to stay apart. In the normal case the upper magnet will flip over and stick to the lower magnet, however ... over certain limits ..... the rigidity of the rotating top ... will stop it toppling and therefore it levitates above the lower magnet. A lot of variables are involved, such as the vertical field must be very close to vertical to reduce top drift. This is not always the same as a perpendicular line from the base ... because manufacturing tolerances, proximity to adjacent metal objects etc., can produce their own effects. The effect only works within certain RPM limits and it was found that better results could be obtained by spinning the top using the fingers than using the battery powered 'spinner'.

During the levitation of the top, it is effectively working on an 'air bearing' which is almost frictionless. This means that the levitating top can be affected by room air currents etc.. We managed levitations lasting about a minute at a time, but the record is in excess of 500 days ..... and still spinning as the photo below shows. This is a modified Levitron, with a copper ring and draft proof cover .... Well done Nate !.

As an example of how well magnetic fields pass through the human body, here is a photo of the top levitating above my hands. The base ring magnet is beneath my hands ....

The green and red objects on the top are weighting washers. Legend has it that a chap spent a chunk of his life playing with and developing it ... until he finally got it to work ... and never made a penny from it !. Sad isn't it.

Diamagnetics.

Some materials, such as 3000 year old vegetation, dead bodies and bismuth have the quality of repelling magnetic fields of both polarities. So do Bismuth, Mercury, Silver, Carbon, Lead and Copper (remember the copper ring in Nates's modified Levitron) ?. One of the better ones is pyrolytic graphite. With a razor blade and some care, one can slit this into thin leaves in much the same way as slate is cleaved. 

If it is true about diamagnetic materials, then it means that a piece of such material could levitate above a magnet !. Of course, the effect is stronger with some materials that others and it really helps to have strong magnets for the experiment, such as neodymium. The classic way of presenting this experiment is to group four cubical magnets together and float a thin wafer of pyrolytic graphite above them. The effect is enhanced if insulating separators are used between the magnets.

As mentioned earlier the human body is also diamagnetic and one demonstration often shows a close-up photograph of a neodyminiun magnet levitating between the thumb and forefinger. What is not shown in many of these photographs is another magnet above the fingers that actually 'supports' the weight of the levitating magnet. The diamagnetic effect just keeps the magnet away from the fingers. Kits are available to create pocket sized demonstration examples for this effect or you can make your own. You will find many sources on the Internet on how to do this. The levitation of the diamagnetic frog is also quite well known now and is referred to in many sources.

So was Earnshaw right or wrong .... the decision is yours !