home    Nederlands

Floating sphere

Dutch zwevende kogel

A problem with two solutions

Many magnets are strong enough to lift another magnet or a steel ball. If you try to do that, you 'll notice that in both cases the attracting force (or repelling force between two equal magnetic poles) increases with diminishing distance. This makes it impossible to simply hang small magnet or ball under a magnet and let it float in mid air. Also repulsion would not work. Try it.
There are two solutions to this problem.


First of all some non-magnetic materials actually repel a magnet when it gets nearer. These substances like bismuth and certain configuations of carbon are called diamagnetic . Substances that are attracted by a magnet like iron and nickel (quarter dollar coin) are called ferromagnetic . Ferrum is latin for iron.
That is very nice and on the internet you can find videos of floating magnets.
But in this way you cannot let a steel sphere float. You can let the magnet rotate by blowing through a drinking straw, as shown in the video. But the rotation soon comes to a halt due to the air resisitance. A sphere would keep rotating much longer. For that we have an other solution.


floating-sphere_files/img023cropped-Cge170-ero2.jpg Use an electromagnet in stead of a fixed magnet. The magnetic field is the same. But by regulating the current by an electronic circuit we can ensure that the attracting force actually diminishes when the distance decreases and vice versa.
You can measure that distance optically. The result is a steel ball that seems to float above a bundle of light.
This steel ball with a diameter of 9½ mm can also be set in motion with a drinking straw. However the rotation is hard to see because the sphere is spotless.
That is why I also have a sphere with a dot of nailpolish. Then the rotation is easy to see. It takes a long time before the sphere stops. Unless the rotation gets unstable, which sometimes happens. The aluminium ring is there to catch it.
home (English)    Nederlands