As a child I loved playing about with magnets – I still do. They can move heavy objects – such as lifting cars at a scrap yard. They can also move light (-weight!) objects – the focusing coils in an electron microscope (something that I must have a go at building) or the deflection coils on a cathode ray tube. Magnetism is a fascinating subject.
As we all know, like magnetic poles repel and opposite poles attract. The one thing that I always wanted to do, as a child, was to use the ‘like pole repulsion’ to make a magnet float – to defy gravity.
With all of my superior intelligence (now, stop laughing), even I could not do that. But, there is a rather clever toy that can…
Spin Stabilised Magnetic Levitation
An American, named Roy M. Harrigan, in the 1970’s, came up with an amazing idea: let’s combine magnets and gyroscopes. The result was the Levitron.
In fig.1, my crude drawing (to say the least) shows the toroidal magnetic field around the base (B). There is a spinning top (S). This contains a small magnet – with like poles to the base. It rotates at about 1000 RPM.
You start it rotating where there is hardly any magnetism – point (C). Now, everything has to be perfectly balanced.
The base (B) has to be perfectly level. The weight of the spinning top has to be perfect. Temperature coefficients, that affect the strength of the magnetic fields involved, have to be balanced.
Not easy. If you can do it, the upward ‘push’ of the magnets combined with the angular momentum of the ‘spinning top’ will cancel the downward force of gravity. In other words, zero.
Angular momentum stops the ‘spinning top’ from flipping over. This, combined with the magnetic force, keeps it floating in mid-air. Beautiful!
Here’s my good self with a demonstration:
Doc Mike demonstrating a ‘Levitron’
We began with the toy gyroscope. I’m sure that some of you will remember it from Christmas’s past. We then moved on to Foucault’s pendulum and gyroscopic inertia. This not only proves that the earth is rotating but, with simple mathematics, that it is indeed spherical. Finally, we mixed gyroscopes and magnets. What more could an adult child, like myself, want?
Okay, thank you all at Going-Postal. I haven’t, currently, got any interesting projects on the go. Who knows what my brain will start to think about – scary. Well it scares the heck out of me!
Have a great spring/summer everyone and I hope that we can keep sharing our knowledge.
© text & images Doc Mike Finnley 2022