Synopsis: Grainy picture

Experiments and modeling point to the optimal shapes for enhancing lift or drag forces on objects moving in granular media.
Synopsis figure
Credit: Y. Ding et al., Phys. Rev. Lett. (2011)

Lift and drag—the forces that allow an airplane to take off and land—are normally associated with an object moving in a liquid or gas. Now, a team of scientists reports in Physical Review Letters how an object’s shape affects these forces when it moves through a granular medium, like sand or beads.

Yang Ding and his colleagues at the Georgia Institute of Technology, US, designed a simple experiment to measure the upward (lift) and shear (drag) forces on differently shaped rods moving through a bed of millimeter-sized glass beads. The rods, which had either a circular, square, or half-circle cross section, were suspended from a moving platform and dragged—with their long axis perpendicular to the direction of motion—through the beads. A force sensor on the platform measured the resultant lift and drag forces on the moving rods, which Ding et al. compared with numerical simulations and a theoretical model.

The group finds that lift is downwards on the half-cylinder rod, but upwards on the square and circular rods. Variations on this type of study could help scientists understand how body shape aids a sand-burrowing animal or how to optimize the design of desert-roving robots. – Jessica Thomas


More Features »


More Announcements »

Subject Areas

Soft MatterInterdisciplinary Physics

Previous Synopsis

Atomic and Molecular Physics

Chemistry class

Read More »

Next Synopsis

Atomic and Molecular Physics

An old transition in a new light

Read More »

Related Articles

Synopsis: Reversible Self-Assembly of Macroscopic “Polymers”
Soft Matter

Synopsis: Reversible Self-Assembly of Macroscopic “Polymers”

Reconfigurable materials step closer to reality with a colloidal system that self-assembles, disassembles, and reassembles into polymer-like chains in response to temperature changes. Read More »

Synopsis: Knotted Loops Fall Flat
Biological Physics

Synopsis: Knotted Loops Fall Flat

A knotted loop of metal beads—mimicking a knotted molecule—organizes into a flat horizontal ring when drifting down through a viscous fluid. Read More »

Focus: Astronomy Students Not Learning the Basics
Interdisciplinary Physics

Focus: Astronomy Students Not Learning the Basics

Nearly half of middle school students in a Norwegian study thought that planets are bigger than stars, even after astronomy instruction. Read More »

More Articles