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4 May 2020, 14:56

The SFK Project: #4 Magic Levitation

What you need:

  • An old bathing shoe (flip-flop)
  • A pencil
  • 4 disk magnets with 2cm diameter (297-9043)
  • 2 ring magnets which need to slide onto the pencil (Neodym, must be axially polarised!!! Just google for a magnet shop)
  • Hot-glue
  • Utility knife
  • compass

What you will get at the end:

A pencil is levitating in the air without any batteries and electronic.

How to build:

Get rid oF the top of the shoe. We need just the sole.

Let the kids play around with the disk magnets. They are ferrite type magnets which are not very strong. The ring magnets are Neodym type and much stronger. You need to be careful not to let them cling together because it would be hard to get them apart again and the kids might squeeze their skin between two magnets. They can use one of the Neodym magnets under and the other one over a table plate. Demonstrate to the kids how you can magically move one magnet using the other one underneath the table. Explain that must be an invisible force causing the magnets to attract or repel each other. We are going to use this force now to levitate a pencil.

Push the two ring magnets onto the pencil. The best practice is to choose the direction in that way that the magnets repel each other. They must fit firmly, and if they don’t, you can pinch a match or wire or piece of paper between magnet and pen. As you can see, I needed to cheat a little bit because my magnets didn’t have holes for the pencil. So I cut the pencil in three parts and glued everything together with hot glue. Engineers never give up ;-)

Now you make a slit into the top side about 10 cm away from the tip of the shoe where you can push the disk magnets in (see picture). You need to cut a second slit into the top side about 6 cm away from the first one, further toward the back of the shoe. About 5 cm away from the tip you cut into the bottom (sole) of the shoe. This cut must be deep enough to be able to flip the tip straight upward (see picture). Use hot-glue to lock the tip in this position firmly.

Alternatively, you may use a piece of broken CD as “front wall” like in the picture below. But losing the friction between the pencil and the front wall will make the balancing of the magnetic forces much more difficult.

You need to find out the right orientation of the magnets now: take one of the disks and hold it against the front ring magnet. The way it clings on that ring is the orientation in which it needs to be placed into the slit. Make the same test with the second magnet. It needs to be oriented in the same direction as the first. Both magnets should rest about 2 cm apart in the front slit. They will attract the front ring magnet later.

Find out the correct orientation of the back two disk magnets the same way but use the back ring magnet to test the disks’ direction. This time we need to turn the disks 180° from the orientation in which they got attracted by the ring magnet. The two back disk magnets will repel the back ring magnet later. The result should look like this:

Before the pencil can levitate, you need to adjust the ring magnets’ positions on the pencil carefully.

Push the pencil against the bent-up tip of the shoe. The back ring magnet needs to be precisely above the back two disk magnets. The front ring magnet must not be above the two disk magnets but a little further toward the back of the shoe. If the pencil doesn’t want to levitate, try changing the distance between the two adjacent disk magnets. If this does not help, you may cheat a little bit by peeking the tip of the pencil into the foam of the shoe tip to hold it in place. You might need a little patience. But that’s what miracles always need. Once you have found the optimum position for all magnets, you can lock their position with a little bit of hot-glue.

At the end of your efforts, your children will love you for the result (your spouse too). So that’s the best time to teach your children the science behind this miracle.

How it works:

There is an invisible force which exists and takes effect between objects even if they are far away. This force is called “magnetism”.  It is challenging to understand how this force is generated and why it can span over vast distances. You will not even learn this secret at school. The good thing is we do not need to understand how it works, just that it works. The magnet spreads this force all around it. That is called “magnetic field”. The force gets smaller and smaller the further you get away from the magnet. It works exceptionally well between two magnets, but it also attracts certain metals like iron. Try some coins! The ring magnets will attract some of them but others not. It depends on the type of metal used for the coins. By the way: Our earth is a giant magnet. That is why the compass needle (which is also a little magnet) always points to the north.

For our little miracle, it is not only important that magnets work over a distance but also that they do not only attract each other but also can repel each other. Magnets have “poles” like the giant earth magnet has a Northpole and a Southpole. Magnets have such two different ends. The north pole always wants to get to the south pole while it wants to escape from another north pole. And a south pole hates other south poles while it wants to join north poles. Identical poles repel each other while different poles attract each other.

That’s what we use for our pencil. We have oriented the disks in such a way that the repelling and attracting forces are balanced. By changing the distances, we adjusted the forces to get them carefully balanced. In the end, the sum of the magnetic forces needs to level out the gravity force which wants to get the pencil down to the floor.

By the way:

Neodym is a chemical element like oxygen or carbon. Its letter code is Nd (oxygen is O, and carbon is C). A Neodym magnet also contains other components like iron (Fe) and an element called “boron” (B).

The magnetic force is measured in “Tesla” (actually you measure what is called “flux density”). Our Neodym magnets do have something about 1 Tesla. That is 20,000 times more than the magnetic field our earth has. The magnets used in clinical MRT scanners for looking into your body have 3 to 7 Tesla. You need to get all metal objects out of your pockets before you enter a room with such a magnet or it will make the metal objects (like a coin) flying out of your pocket, crossing the room like a bullet and end up clinging at the magnet. The attraction force is so strong that you could not get the coin off from the magnet.

Where did I find the idea:

What's coming up:

Next week we will build a magic trick from a bottle and a balloon.

Volker de Haas started electronics and computing with a KIM1 and machine language in the 70s. Then FORTRAN, PASCAL, BASIC, C, MUMPS. Developed complex digital circuits and precise analogue electronics for neuroscience labs (and his MD grade). Later database engineering, C++, C#, hard- and software developer for industry (transport, automotive, automation). Ended up designing and constructing the open source PLC / IPC "Revolution Pi". Today engaged in advanced development as a service.

4 May 2020, 14:56


May 28, 2020 09:10

Which coins are magnetic?

0 Votes

May 28, 2020 21:38

@marky_r good question. Have a look here: