Sci: Refrigerator magnets

Have you ever tried sticking a fridge magnet onto a refrigerator with the black side out? If you haven’t, try it, but it won’t work. It seems as if the makers don’t want you sticking the magnets so the advertising can’t be seen. The oddest thing is that two fridge magnets will always stick to each other because of the way they are made, with a series of magnetic strips, about 2 mm apart:

A cross-section of the strips in a fridge magnet

If you pull two attracting fridge magnets across each other the right way, you will feel a sort of bumpy ride as attraction replaces repulsion and back again. Line them up, try pulling one across the other, and if you don’t get the rattle effect, try moving one of them at 90º to the way you first moved, then turn one of them 90º and try different directions.

The arrangement on the left showed no effect, the right one ‘rattled’.

If that doesn’t work, replace one of the magnets. Some of the ones I tried failed to work, and I have no idea why, but I wondered if the ‘stripes’ might be in concentric circles. The most curious thing of all, until you think about the way the strips are made, is that when you have the magnets aligned, the chattering only works in one direction.

Some notes:

Fridge magnets: https://engineerdog.com/2015/03/12/why-do-refrigerator-magnets-only-stick-on-one-side/. (Last accessed April 2025.) If you don’t want advertising on your fridge, use a fingernail to peel off a corner of the printed message.

Think of the stripes as bunches of horseshoe magnets lined up beside each other. A friend tells me that if you have a lot of iron filings, you can cover a fridge magnet with iron filings, and see the stripes. I didn’t have time to get any iron filings, but I know that garden soil often has lots of magnetic particles in it.

Make a discovery: wrap a handkerchief (or cling wrap) around a bar magnet, and pass it through some dry soil. If anything sticks to the magnet, unwrap the magnet carefully and collect the particles, taking care not to let them stick to the magnet. The fragments will, of course, make a mess of the fridge magnet when you sprinkle the filings or fragments on it. Use an old magnet!

Note: If you want more detail about refrigerator magnets, the terms to use are <Halbach array> and <one-sided flux distributions>. And by the way, the first Halbach array was designed for use in focusing the beams in particle accelerators. That’s neat!

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