Some shallow knowledge and perception of magnetic levitation?

For some reason, I had to get into the field of magnetics and plan from scratch. At first I only felt ordinary, but the more I came into contact with it, the more mysterious and magical it became. When I went deeper, I only felt that my knowledge was superficial, and it was natural.

The initial understanding of magnetic levitation may be a little naive and superficial, simply thinking that repulsion can levitate. After checking the information and preliminary experiments, I found that the magnetic field, the magnetic force, is not as simple as imagined.

First of all, the magnetic field and the electric field are closely related, and the magnetism generates electricity, and the electricity generates magnetism have been learned in high school. In fact, it involves the theory of relativity: the magnetic field is the direct result of the relativistic effect of the electric field. Static charges create electrostatic fields; moving charges create electromagnetic fields. If a person is stationary relative to the electric charge, then he cannot observe the magnetic field. If the other person is not stationary relative to the electric charge at this time, he also observes the magnetic field when he observes the electric field. For the content of the theory of relativity, you can refer to “Feynman Lectures on Physics”, which is easier to understand about the theory of relativity.


Regarding the magnetic force, the repulsive force of the magnetic levitation is not so simple to use for the magnetic levitation. Because repulsion and suction are not linear, repulsion decreases rapidly with distance, and suction does the opposite. If this is the only reason, then there is not much difficulty in magnetic levitation, but there is a theorem: Enshao’s theorem. He described it this way: The stable suspension of a moving object cannot be achieved entirely by the electromagnetic force between permanent magnets or permanent magnets and soft magnets. In terms of expansion, the equipotential surface of the magnetic field is saddle-shaped, and there is a “saddle point” in the gravitational potential energy, that is, there is a stable equilibrium in one direction, and an unstable equilibrium in the other direction. With regard to balance, it can be divided into casual balance, stable balance and unstable balance. Casual balance is like a small ball rolling on the flat ground, and it can eventually balance wherever it goes; stable balance is like a small ball under a single pendulum, which can achieve stable balance at the lowest point of gravitational potential energy; unstable is to swing to the highest point place. Obviously the “saddle point” on the saddle is the point of unstable equilibrium. This theorem is really frustrating. You can’t rely on permanent magnets alone, that is, magnetic levitation is extremely difficult.

Of course, there are special cases that do not conform to this theorem – superconducting magnetic levitation. The so-called superconducting material needs to meet two conditions: 1. The resistance is zero. 2. Repel magnetic field lines. Zero resistance means that no energy is lost in the superconductor. Repelling the magnetic field lines can make it levitate, which is the Meissner effect. In addition, because the situation is not always so ideal, there is always a small amount of magnetic field lines entering the superconductor, and the superconductor can prevent the movement of the magnetic field lines from changing, because the change means a loss of power. What good is this? Just like in rough seas, the balance of the boat’s suspension alone is definitely not as good as the boat docked on the shore. Superconductors can lock magnetic field beams to achieve static equilibrium, which involves quantum mechanics, that is, quantum levitation and quantum locking.

Post time: Sep-06-2022