Synopsis: U-shaped Grains Get Clingy

Piles of staples stand up to shaking better if the staple prongs have an intermediate length.
Synopsis figure
N. Gravish, Georgia Institute of Technology

The shape of grains in granular materials can have a large effect on their collective physics. A new study explores u-shaped grains and how they bind together through entanglements. In experiments described in Physical Review Letters, the researchers found that free-standing piles of metal staples held together longest when the staple “arms” had a particular length. To explain this optimum shape, the authors develop a model that may apply to other collections of irregular shaped objects.

Physicists have long been interested in how sand pours down a slope or how nuts pack inside a box. However, not much work has been done with “bent” or concave grains that can intertwine. Examples include polymer networks and anisotropic colloids, as well as the rafts that certain ant species form by interlocking limbs and mandibles.

Nick Gravish of the Georgia Institute of Technology in Atlanta and his colleagues decided to investigate a simple concave grain: the common staple. In their experiments, the researchers varied the length of the staple arms, while keeping the width constant. The team formed piles of uniform staples and then shook them up and down until the piles eventually collapsed. Staples with a length-to-width ratio of about 0.4 remained upright the longest. The scientists explained their observations using simulations and theory. It turns out that lengthening the arms of a staple increases the number of entanglements with neighbors, but conversely decreases the packing density. Staples that balance these two effects create the most stable piles. – Michael Schirber


Announcements

More Announcements »

Subject Areas

Materials Science

Previous Synopsis

Quantum Information

Polarized Light in Safe Storage

Read More »

Next Synopsis

Atomic and Molecular Physics

Wave of Correlation

Read More »

Related Articles

Synopsis: Electron–Phonon Affair Comes to Light
Condensed Matter Physics

Synopsis: Electron–Phonon Affair Comes to Light

Photoelectron spectroscopy reveals the details of the interaction between electronic and vibrational excitations in a molecular material. Read More »

Synopsis: Topological Origami
Materials Science

Synopsis: Topological Origami

Origami formed by folding and cutting a material can feature well-defined, tunable mechanical properties. Read More »

Synopsis: Whisky-Inspired Coatings
Fluid Dynamics

Synopsis: Whisky-Inspired Coatings

As a whisky drop dries, a combination of molecules in the liquid ensure a spatially uniform deposition—a finding that could inspire coating technologies. Read More »

More Articles