Collection Spotlight: Magnetron

The Magnetron seems extremely trivial, but is anything but that.


The Magnetron toy consists of a wood block with two spinners, having three arms each. At the end of the spinners is a really strong magnet. The outward face of all the magnets on the magnetron are the same. This means when arms of the two spinners come near to each other, there is a strong repelling force felt by the arms.

At this point, you might think “So what?”. Clearly, there’s nothing special about these arms. But something very interesting happens when you give one the spinners a light spin. The motion of the spinners appears to be completely random. Sometimes, a spinner will spin really fast, then suddenly slow down. Sometimes, it could be spinning very fast, then suddenly change direction. What’s more, (within reason) you could never spin a spinner and produce the same behaviour of the spinners two times in a row.

This toy demonstrates what we call chaotic motion. There are many different demonstrations of chaotic motion. One of the more popular demonstrations of such motion is the double pendulum, which looks something like this:

The reason why the motion is called chaotic is because the motion is, literally, chaotic. That is, it is impossible to predict how the pendulum (or in the case of this post, the spinners) will behave as time goes on. Technically, though, that is not true. If you were given all the information of the system, you could theoretically calculate the motion of the system. The problem is that there are just too many variables to consider and the calculations become near-to-impossible to do.

To elaborate further, let’s just talk about the spinners on the Magnetron. If you wanted to predict the motion of the spinners, you’d need to know a lot of things. For example:

  • The inital speed of the spinner
  • The initial height the spinner was at before you let go
  • How quickly it springs back up to its normal height
  • The exact position of the other spinner
  • The exact strength of each magnet on each spinner
  • …and the list goes on

You could even argue that the position of the air molecules in the room matter, because the air resistance can affect the motion of the spinner and you’d be right.

For all intents and purposes, it is impossible to predict the motion of these systems, and if you vary the initial conditions by even a tiny amount, you get a massively different response. You might think that randomness in a system is pretty useless, but it actually has many applications. Chaos Theory is a study in mathematics that has applications in areas like cryptography (which studies encryption) and biology (which studies randomness in mutations).

The Magnetron is such a simple toy, but demonstrates an extremely complicated process that is impossible to predict.

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