Levitation is the overcoming of gravity, in which the subject or object is in space without support. The word “levitation” comes from the Latin Levitas, which means “lightness”.
It’s wrong to equate levitation to flight, because the latter is based on air resistance, which is why birds, insects and other animals fly, rather than levitate.
Levitation in Physics
Levitation in physics refers to a stable position of the body in a gravitational field, while the body should not touch other objects. Levitation implies some necessary and elusive conditions:
- A force that can compensate for gravitational attraction and gravity.
- A force that can ensure the stability of the body in space.
It follows from the Gauss law that in a static magnetic field, static bodies or objects are not capable of levitation. However, if you change the conditions, then you can achieve levitation.
Quantum levitation
The general public about quantum levitation first became known in March 1991, when an interesting photo was published in the scientific journal Nature. Don Tapscott, director of the Tokyo Research Laboratory for Superconductivity, stood on a ceramic superconducting plate, and there was nothing between the floor and the plate. The photo turned out to be real, and the plate, which, together with the director standing on it, weighed about 120 kilograms, could levitate above the floor due to the superconductivity effect, known as the Meissner-Oxenfeld effect.
Diamagnetic levitation
This is the type of suspension in a magnetic field of a body containing water, which in itself is a diamagnet, that is, a material whose atoms are able to magnetize against the direction of the main electromagnetic field.
In the process of diamagnetic levitation, the main role is played by the diamagnetic properties of conductors, the atoms of which under the influence of an external magnetic field slightly change the parameters of the motion of electrons in their molecules, which leads to the appearance of a weak magnetic field, which is opposite in direction to the main one. The effect of this weak electromagnetic field is enough to overcome the force of gravity.
To demonstrate diamagnetic levitation, scientists repeatedly conducted experiments on small animals.
This type of levitation was used in experiments on living objects. During experiments in an external magnetic field with an induction of about 17 Tesla, a suspended state (levitation) of frogs and mice was achieved.
According to Newton’s third law, the properties of diamagnets can be used and vice versa, that is, to levitate a magnet in the field of a diamagnet or to stabilize it in an electromagnetic field.
Diamagnetic levitation is inherently identical to quantum levitation. That is, as with the Meissner effect, absolute displacement of the magnetic field from the material of the conductor occurs. A small difference is that in order to achieve diamagnetic levitation, a much stronger electromagnetic field is needed, however, it is not necessary to cool the conductors to achieve their superconductivity, as in the case of quantum levitation.
At home, you can even put several experiments on diamagnetic levitation, for example, in the presence of two bismuth plates (which is a diamagnet), a magnet with a low induction, about 1 T, can be suspended. In addition, in an electromagnetic field with an induction of 11 Tesla, it is possible to stabilize a small magnet in suspension, adjusting its position with your fingers, without completely touching the magnet.
Often diamagnets are almost all inert gases, phosphorus, nitrogen, silicon, hydrogen, silver, gold, copper and zinc. Even the human body is a diamagnet in the right electromagnetic magnetic field.
Magnetic levitation
Magnetic levitation is an effective method of lifting an object using a magnetic field. In this case, magnetic pressure is used to compensate for gravity and gravity.
According to the Earnshaw theorem, one cannot hold an object in a gravitational field stably. That is, levitation is impossible under such conditions, however, if we take into account the mechanisms of action of diamagnetics, eddy currents and superconductors, then effective levitation can be achieved.
If magnetic levitation provides lift with mechanical support, this phenomenon is called pseudo-levitation.
Meisner effect
The Meissner effect is the process of the absolute displacement of the magnetic field from the entire volume of the conductor. Usually this occurs during the transition of the conductor to the superconducting state. This is precisely why superconductors differ from ideal ones - despite the fact that both have no resistance, the magnetic induction of ideal conductors remains unchanged.
For the first time this phenomenon was observed and described in 1933 by two German physicists - Meisner and Ochsenfeld. That is why sometimes quantum levitation is called the Meissner-Oksenfeld effect.
From the general laws of the electromagnetic field, it follows that if there is no magnetic field in the volume of the conductor, only the surface current is present in it, which occupies the space at the surface of the superconductor. Under these conditions, the superconductor behaves in the same way as a diamagnet, while not being such.
The Meissner effect is divided into full and partial, depending on the quality of superconductors. The full Meissner effect is observed when the magnetic field is completely displaced.
High temperature superconductors
There are few pure superconductors in nature. Most of their materials with superconducting properties are alloys, in which most often only a partial Meissner effect is observed.
In superconductors, it is precisely the ability to completely displace the magnetic field from its volume that divides the materials into superconductors of the first and second types. The superconductors of the first type are pure substances, for example, mercury, lead, and tin, capable of demonstrating the full Meissner effect even at high magnetic fields. Superconductors of the second type are most often alloys, as well as ceramics or some organic compounds, which in a magnetic field with high induction are capable of only partially displacing the magnetic field from its volume. Nevertheless, under conditions of a very small magnetic field induction, almost all superconductors, including the second type, are capable of the full Meissner effect.
Several hundred alloys, compounds, and several pure materials with the characteristics of quantum superconductivity are known.
Experience "The coffin of Mohammed"
“The coffin of Mohammed” is a peculiar trick with levitation. So called experience, demonstrating the effect.
According to Muslim legend, the tomb of the prophet Magomed was in the air in limbo, without any support and support. That is why experience has such a name.
Scientific explanation of experience
Superconductivity can only be achieved at very low temperatures, so the superconductor must be cooled in advance, for example, using high-temperature gases such as liquid helium or liquid nitrogen.
Then, a magnet is placed on the surface of a planar cooled superconductor. Even in fields with a minimum magnetic induction not exceeding 0.001 Tesla, the magnet rises about 7-8 millimeters above the surface of the superconductor. If the magnetic field induction is gradually increased, the distance between the surface of the superconductor and the magnet will increase more and more.
The magnet will continue to levitate until the external conditions change and the superconductor loses its superconducting characteristics.