Skip to Content
Uncategorized

The Unexpected Behaviour of Beads in a Box

Fill a narrow box with beads and set it spinning and the resulting patterns are surprising, beautiful and unexplained.

In 1939, the Japanese researcher Yositisi Oyama, showed that a rotating drum half-filled with beads of different sizes causes the beads to demix forming into various patterns of segregation. This is a potentially interesting way to separate such mixtures. This and other work kickstarted an entirely new field focused on the strange behaviour of granular fluids.

Now, Frank Rietz and Ralf Stannarius at the Department of Nonlinear Phenomena at the University of Magdeburg in Germany have found a curious corollary to this work.

Instead of a rotating drum, they confine their mixture of small and large beads to a flat box which they then set rotating at slow speed so inertial effects are minimised. And instead of half filling the box, they almost totally fill it with beads.

You might imagine that the beads would jam, preventing any separation but what actually happens is quite extraordinary. Above some filling threshold, the bead separation flow begins to show a rich pattern of convection.

All this is beautifully filmed and explained in a fluid dynamics video which is well worth looking at (if only to see how scientific publication is changing.)

Rietz and Stannarius say they have been unable to explain these patterns using the known mechanisms of granular convection. So they’re left with a puzzle: how do these patterns emerge?

The answer may be of more than passing interest to earth scientists since similar convection patterns emerge on large scale in Earth’s atmosphere. Whether there is any link, however, has yet to be established.

An interesting puzzle for fluid dynamicists with a few hours to spare.

Ref: arxiv.org/abs/0910.4897: Convection Rolls in a Rotating Box Filled with Beads

Keep Reading

Most Popular

AGI is just chatter for now concept
AGI is just chatter for now concept

The hype around DeepMind’s new AI model misses what’s actually cool about it

Some worry that the chatter about these tools is doing the whole field a disservice.

Workers disinfect the street outside Shijiazhuang Railway Station
Workers disinfect the street outside Shijiazhuang Railway Station

Why China is still obsessed with disinfecting everything

Most public health bodies dealing with covid have long since moved on from the idea of surface transmission. China’s didn’t—and that helps it control the narrative about the disease’s origins and danger.

Europe's AI Act concept
Europe's AI Act concept

A quick guide to the most important AI law you’ve never heard of

The European Union is planning new legislation aimed at curbing the worst harms associated with artificial intelligence.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.