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

A Roomba recorded a woman on the toilet. How did screenshots end up on Facebook?

Robot vacuum companies say your images are safe, but a sprawling global supply chain for data from our devices creates risk.

A startup says it’s begun releasing particles into the atmosphere, in an effort to tweak the climate

Make Sunsets is already attempting to earn revenue for geoengineering, a move likely to provoke widespread criticism.

10 Breakthrough Technologies 2023

Every year, we pick the 10 technologies that matter the most right now. We look for advances that will have a big impact on our lives and break down why they matter.

These exclusive satellite images show that Saudi Arabia’s sci-fi megacity is well underway

Weirdly, any recent work on The Line doesn’t show up on Google Maps. But we got the images anyway.

Stay connected

Illustration 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.