Printer Friendly

Random packing of spheres.

The familiar arrangement evident in piles of neatly stacked oranges at a supermarket represents the tightest possible packing of identical spheres (SN: 8/15/98, p. 103). The ordered spheres occupy 74 percent of the total space available. The fraction of space typically filled by randomly packed spheres--whether peas poured into a bag or ball bearings into a tin--has proved much more difficult to pin down.

Now, chemist Salvatore Torquato and his coworkers at Princeton University argue that traditional, empirical methods of achieving random packings--pouring followed by shaking for a sufficiently long time, for example--fail to give consistent results. The pouring rate and the amplitude and frequency of vibration can readily affect the final answer, they contend. Computer simulations of random packings reveal similar problems.

To make the notion of random packing more consistent and mathematically precise, Torquato and his colleagues have introduced the concept of what they call a "maximally random jammed" state. A given sphere is jammed if it can't move when all the other spheres are fixed. The researchers focus on the most disordered arrangement in which all spheres are immobilized. The packing fraction for this state is about 64 percent.

The researchers report their findings in the March 6 PHYSICAL REVIEW LETTERS.
COPYRIGHT 2000 Science Service, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2000, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
Printer friendly Cite/link Email Feedback
Author:I.P.
Publication:Science News
Article Type:Brief Article
Date:Apr 1, 2000
Words:206
Previous Article:Orbiting in a figure-eight loop.
Next Article:Less Massive than Saturn?
Topics:


Related Articles
Curves for a tighter fit: number theory provides a novel strategy for packing spheres efficiently.
Loosely packed spheres.
The Codemart catalog: arranging points on a sphere for fun and profit.
Cracking Kepler's sphere-packing problem.
Packing spheres around a sphere.
M&Ms pack more tightly than spheres.
Squashed spheres set a record for filling space.
Oddballs: it's easier to pack spheres in some dimensions than in others.
Messiness rules: in high dimensions, disorder packs tightest.
Lord, I Give You This Day.

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters