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How Do 'Singing Magnets' Work?
dpbsmith asks: "Singing magnets are available at all of the usual geek-toy emporia, and, for all I know, ordinary toy emporia as well. They consist of a pair of magnets made of a polished substance with the general appearance of hematite. What is surprising, pleasing, and unexpected is that when the magnets strike each other under their own power, they produce a sharp, loud buzz that rises in pitch. The sound lasts a good fraction of a second and climbs somewhere into what sounds like the 200-500 Hz range. The exact sound and its duration are somewhat unpredictable and depend on how the magnets happen to strike each other. It is a little like the sound that you get when you mash a pingpong ball against a pingpong table with a paddle. What physics are involved in the production of these sounds?"
"Google searches turn up some forum postings that indicate that it is a synthetic magnetic substance similar to hematite that's available cheaply in China as an industrial byproduct. The singing magnets are a little larger than size of olives; the shape is similar to a (U. S.) football but slightly more elongated. Their major axis is about 5 cm long, their minor about 1 cm. They are fairly powerful and will jump together when placed on a desk about three inches apart. They can distort the colors on a CRT display from a distance of over 20 cm.
Contrary to expectation, the poles of the magnets are oriented along one of the minor axes of the ellipsoid, not the major axis.
Neodymium magnets in 'ordinary' shapes produce boring 'plinks' when they snap together. Something about the shape of these magnets makes the sound much longer-lasting and entertaining. It is not simply the bounding rebound of two objects made of stiff-but-elastic material. Transfers of linear to angular momentum are clearly involved.
If course, I'd love to know whether these things were 'invented' or 'discovered', and by whom, trying to do what.
Contrary to expectation, the poles of the magnets are oriented along one of the minor axes of the ellipsoid, not the major axis.
Neodymium magnets in 'ordinary' shapes produce boring 'plinks' when they snap together. Something about the shape of these magnets makes the sound much longer-lasting and entertaining. It is not simply the bounding rebound of two objects made of stiff-but-elastic material. Transfers of linear to angular momentum are clearly involved.
If course, I'd love to know whether these things were 'invented' or 'discovered', and by whom, trying to do what.
They bounce apart, attract togethor, bounce apart again, etc losing energy each cycle until they can bounce no more.
Okay, that was a wild ass guess.
This is blowing my mind. You would think it should be a constant frequency with decay, like the classical pendulum. The difference between the classical pendulum and this case is that for a pendulum, the force is constant; with the magnet, the force is inversely proportional to the distance between the magnets. As the energy in the velocity (E=1/2mv^2) is converted to heat, the magnets have a lower velocity so they travel a shorter distance away from the other magnet. The closer the magnets are, the greater the force, again reducing the period between "clacks". The frequency increases because the magnets have a non constant in the force between them (the force increases as the reciprocal of the square of the distance).
I'm sure that the guys who are selling audiophile lacquer for $200/oZ and wooden potentiometer knobs for $500 a piece will have a much more amazing explanation involving quantum audiodynamic subparticle field wavetransformation theory, that not only makes your audio equipment sound more open and free flowing with a nice improvement in resolution, better dynamics and improved overall naturalness, but also improves the taste of wine making it older in a matter of seconds (a widely known property of magnets), but I--a boring scientist--will only tell you this: they bounce.
Sincerely,
Pan Tarhei Hosé, PhD.
"Homo sum et cogito ergo odi profanum vulgus et libido."
Despite what you say, they are just bouncing off each other.
Additionally, the central location of the poles helps to maintain equilibrium and reduce the range of possible contact points.
(Unlike a round magnet which would have a wider range of effective contact points thus allowing more slop in the bounce cycles with a coincident reduction in tonal quality).
Fascinating stuff. An utter load of crap sold at a substantial profit, all through the magic of ubfuscatory language.
they produce a sharp, loud buzz that rises in pitch. The sound lasts a good fraction of a second and climbs somewhere into what sounds like the 200-500 Hz range.
I also don't believe its a simple bounce. If that were so then it should work with any magnets with a a strong surface. I've never heard of this.
Someone pointed out that liquidmetal demos the same rising pitch behaviour. They do this by having an inredibly efficient 99% bounce. But singing magnets have been around for a while before that.
I think the shape allows the magnets to convert their kenetic energy into a rolling motion and back to kenetic without needing to to do a real bounce and avoid elasticity losses.
Think of Tony Hawks doing a half pipe. Vertical to horizontal back to vertical. The magnets with their weird shape collide slightly off center, then pulled by the magnetic fields convert a portion of their energy to the rolling that occurs as they get into a more parallel position and then inertia carries them beyond equilibrium where the kenetic energy throws them apart again. Like a rocking chair but with enough energy to seperate the surfaces. As long as the rolling resistance is low it should be pretty efficient.
Normally shapped magnets don't exibit the same behaviour since their surfaces collide and depend entirely on their modulus of elasticity to rebound them.
I not sure but I also think that the rolling action reduces peek force at contact so what bounce there is can be more efficient.
At least thats my guess..