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Science in the NewsThe Town VoiceThe Complex Made Simple

 

Scientific American Frontiers Revisited

By Arlon Staywell
RICHMOND — An interesting thing happened years ago.  There was an unusual episode of "Scientific American Frontiers" on the Public Broadcasting System.  In Richmond, Virginia it aired February 24, 1999.  One of the topics concerned why larger, heavier objects rose to the top of dry mixtures.  Brazil nuts for example typically rise to the top of a can of mixed nuts though they are larger and heavier than the other nuts.

The group of "scientists" responsible for the explanation given on the program said that the walls of the container set up a convection current that "pushed" the larger objects upward.  I saw the program and immediately realized they were quite wrong.

The next morning, Feb. 25, 1999 according to Compuserve e-mail records, I e-mailed my own explanation to an engineering professor I had met at Virginia Commonwealth University.  I had earlier asked his help in gaining some sort of recognition for my work in electronics and whether I should attend VCU.  Part of the text of that e-mail was as follows:

Last night on "Scientific American Frontiers" I saw people trying to explain why larger, heavier objects rose to the top of agitated mixtures.  Their explanation centered on the sides of the container generating a "current" that produced the result.  I think this was inadequate.  I think it pertained to specific container and agitation types.  I think the better answer, and I hope you'll agree, is as follows  ...
1) Larger, heavier objects have no advantage in falling due to the acceleration of gravity, Galileo demonstrated that.
2) Smaller objects do have an advantage in falling in that more of the spaces created by agitation are likely to be large enough for them to enter.
    And the message further explained:
... we can demonstrate my explanation is better.  We could vary the amount of agitation and show that very low produces no significant change of relative position of larger and smaller particles, and increasingly higher agitation first favors the smaller particles to fall lower then less so as the spaces created by agitation become large enough to accept either size particle.  Also a larger container could be used to show that the "current" created by the sides is too small to be a factor.
    The next day the professor replied:
Thanks for the commentary, and I think your explanation is on target...more so than any "current" idea.  We look forward to welcoming you this fall.
    I was in fact welcomed that fall.  I chose later to major in mass communications with a minor in economics.  I was more concerned that Clinton was president than which nuts were on top of nut mixtures.  Let's not explore the irony in that.  I did not minor in engineering as I earlier planned, but I did substitute science, math and computer courses of engineering majors for the "easier" (not necessarily easier and required permission from the School of Mass Communications) mass communication versions of those courses so that changing to that major would be simple and economical.