Science is Magic! Watch a Magnet Sail Around a Möbius Strip

The entire universe in blog form
July 12 2013 8:00 AM

Watch a Levitating Magnet Sail Around a Möbius Strip!

File this under “OMG this is so cool why didn’t I think of it?!”: a video of a superconducting magnet sailing up, down, and around a track shaped into a Möbius strip:

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

I love this so so so much. It’s all explained in the video (starting around two minutes in) but in case you missed it:

Advertisement

1) There exists a kind of material that, if you chill it down to very low temperatures, becomes a superconductor, meaning electrons can flow through it freely without resistance. What that means is that a lot of weird stuff can occur. For one thing, if you induce an electric current in a superconductor, that current will flow forever without resistance.

As an analogy, imagine filling your sink with water. If you give the water a brief swirl with your hand the water will flow around the sink. Eventually, though, friction slows it and the water will be still once again. But if the water were frictionless, it would swirl forever. A superconductor is like a frictionless sink, filled with electrons instead of water. Once electrons start to flow, making a current, they never stop.

2) Another important thing is that if you stick a conductor in a moving magnetic field (or move a magnet over a conductor), it will induce a current in the conductor, which will start electrons flowing. One of the basic laws of electricity and magnetism is that the flowing electron current (which we call electricity) will itself generate a magnetic field, and it’ll do so in a way to resist the original changing magnetic field. It’s a bit like if you feel yourself falling over, and you flail your arms (or grip something quickly) to get your balance back.

3) Still with me? Now combine this. In a superconductor, if it’s set up properly, you can generate a flow of electrons that’ll whiz around inside it. If you then put that superconductor on a track, it will levitate above the track because gravity pulls it down, changing the magnetic field it feels, so it sets up its own magnetic field to resist that. Same thing if you hang it upside down; gravity pulls it away from the track, so it changes its own field to hold on to the track tighter.

superconductor puck floating over a track
A supercool super-cooled superconducting, um, superpuck.

Photo by The Royal Institution, from the video

4) Finally, if you look at the magnetic field of the track, it changes rapidly near the edges, toward the inside and outside. That acts like a buffer, keeping the superconductor on the track (because, again, the superconductor’s own magnetic field will resist that change, forcing it to the middle of the track). But the field doesn’t change along the track, so the superconductor doesn’t care about moving in that direction. Poke it, and it’ll glide, floating, along the track.

5) Now we can combine everything. Chill a puck made of yttrium barium copper oxide (or as we in the science biz call it, YBCO, to sound—wait for it, wait for it—cool) with liquid nitrogen so that it becomes a superconductor. Put it on the track. The magnetic field lines of the magnets in the track grip the puck invisibly, and it can glide up and down the track. Yay!

All of the above is well-known and most students of physics have seen this demo a zillion times. But the idea of shaping the track into a Möbius strip? That is pure genius! A Möbius strip is a shape that has only one side. Here’s how to make one: Take a strip of paper that is much longer than it is wide. Give one end a half twist, so it’s flipped over, and attach it to the other end. Voila! A Möbius strip. Take a pencil, put the tip anywhere on the strip, and start drawing a line along it. After a moment, you’ll meet up to the point where you started. If you hadn’t twisted the paper, and just attached one end to the other to form a squat cylinder, that won’t happen. There’s an inside face and an outside face. In a Möbius strip there’s only one face, connected to itself.

So in the video, the floating superconductor slides along the track, flips upside down, keeps moving, and eventually comes back to the place it originally started. If you’re impatient, the cool stuff starts at 4:45 in the video.

This is really just a clever way to show an old demo, but I love it. It’s got everything! Exotic materials, liquid nitrogen, superconducting magnets, and a Möbius strip all combined in a live-action Escher drawing. It’s nerdvana.

Hmmm, well, actually, it doesn’t have everything. What it really needs is for the puck to have a little fan on it, a propeller, so it can keep going around and around forever. Or until it warms up and the superconductivity collapses (maybe attach a hose to it somehow to keep it supplied with liquid nitrogen…?). That would make a fun exhibit at a museum, too.

Science! I love this stuff!

Tip o' the Meissner Effect to Philippe Roux on G+.

TODAY IN SLATE

History

The Self-Made Man

The story of America’s most pliable, pernicious, irrepressible myth.

Does Your Child Have Sluggish Cognitive Tempo? Or Is That Just a Disorder Made Up to Scare You?

Mitt Romney May Be Weighing a 2016 Run. That Would Be a Big Mistake.

Amazing Photos From Hong Kong’s Umbrella Revolution

Rehtaeh Parsons Was the Most Famous Victim in Canada. Now, Journalists Can’t Even Say Her Name.

Television

See Me

Transparent is the fall’s only great new show.

Doublex

Lena Dunham, the Book

More shtick than honesty in Not That Kind of Girl.

What a Juicy New Book About Diane Sawyer and Katie Couric Fails to Tell Us About the TV News Business

Rehtaeh Parsons Was the Most Famous Victim in Canada. Now, Journalists Can’t Even Say Her Name.

  News & Politics
Damned Spot
Sept. 30 2014 9:00 AM Now Stare. Don’t Stop. The perfect political wife’s loving gaze in campaign ads.
  Business
Moneybox
Sept. 30 2014 10:44 AM Bull---- Market America is overlooking a plentiful renewable resource: animal manure.
  Life
Atlas Obscura
Sept. 30 2014 10:10 AM A Lovable Murderer and Heroic Villain: The Story of Australia's Most Iconic Outlaw
  Double X
Doublex
Sept. 29 2014 11:43 PM Lena Dunham, the Book More shtick than honesty in Not That Kind of Girl.
  Slate Plus
Behind the Scenes
Sept. 30 2014 10:59 AM “For People, Food Is Heaven” Boer Deng on the story behind her piece “How to Order Chinese Food.”
  Arts
Brow Beat
Sept. 30 2014 10:48 AM One of Last Year’s Best Animated Shorts Is Finally Online for Free
  Technology
Future Tense
Sept. 30 2014 7:36 AM Almost Humane What sci-fi can teach us about our treatment of prisoners of war.
  Health & Science
Bad Astronomy
Sept. 30 2014 7:30 AM What Lurks Beneath the Methane Lakes of Titan?
  Sports
Sports Nut
Sept. 28 2014 8:30 PM NFL Players Die Young. Or Maybe They Live Long Lives. Why it’s so hard to pin down the effects of football on players’ lives.