The mystery of magnetic levitation by rotation

2023-11-15 09:15:39

It all started in 2021, when the Turkish scientist Hamdi Ucar announced an experiment whose results were unusual. He attached a magnet to the rotating end of a motor-driven tool and was thus able to spin the magnet very quickly. The rotary tool used is commonly used and of the same style as an everyday electric drill.

The surprising thing happened when he brought the rotating magnet closer to a second magnet. It also began to rotate but, suddenly, it was suspended in a fixed position just a few centimeters away.

Although magnetic levitation is nothing new (the best-known example is probably Maglev trains, which rely on a strong magnetic force to lift and propel themselves), the experiment baffled physicists, since this phenomenon was not described by physics. classical or, at least, by none of the known mechanisms of magnetic levitation.

A team including, among others, Rasmus Bjørk and Joachim Marco Hermansen, both from the Technical University of Denmark (DTU), was also intrigued by Ucar’s experiment and set out to replicate it and try to find out what exactly is happening.

Replicating it was easy. In fact, it could be made using ordinary components, available at any specialty store, but the physics underlying the phenomenon turned out to be stranger than the study’s authors thought it would be.

“Magnets shouldn’t float when they’re together. Normally, they attract or repel each other. But it turns out that if you spin one of the magnets, you can make it float. And that’s the strange part. The force that affects the magnets It shouldn’t change just by spinning one of them, so it seems there is a coupling between the movement and the magnetic force,” explains Bjørk.

Example of magnetic levitation by rotation. The magnet held at the tip of the rotating tool is rotating at high speed and the other magnet is floating in front of it. (Photo: DTU)

Several magnets of different sizes were used in the experiments, but the principle remained the same: by rotating one magnet very quickly, the researchers observed how another nearby magnet, called a “floating magnet”, began to spin until it levitated and remained suspended at a fixed distance from the other magnet.

The floating magnet was oriented close to the axis of rotation and toward the pole of the same type of the other magnet. Thus, for example, the north pole of the floating magnet, while rotating, remained oriented toward the north pole of the fixed magnet.

This is different from what would be expected based on the laws of magnetostatics, which explain how a static magnetic system works. However, it turns out that magnetostatic interactions between the rotating magnets are responsible for creating the equilibrium position of the floating magnet, as Frederik L. Durhuus of the Technical University of Denmark and co-author of the study verified using simulations of the phenomenon.

The study authors observed that the size of the magnet greatly influences the dynamics of levitation: smaller magnets require higher rotation speeds for levitation.

“It turns out that the floating magnet has a tendency to align itself with the rotating magnet, but it cannot rotate fast enough to do so. So as long as this situation persists, it will float,” explains Rasmus Bjørk. “It can be compared to a top. It does not stay upright if it is not spinning. It only stays in its position thanks to rotation. When the rotation loses energy, the force of gravity (or, in our case, repulsion and the attraction of the magnets) is large enough to overturn that balance.

The new study is titled “Magnetic levitation by rotation.” And it has been published in the academic journal Physical Review Applied. (Source: NCYT from Amazings)