Have you tried the experiment under vacuum or with metal powders? I'm thinking that electric charge builds up as the electrically non-conductive grains try to move past each other, keeping them from moving much until the charge buildup is large enough to overcome air permittivity. This would release the charge and allow grain motion. If this picture is correct you should get a smaller voltage measurement in vacuum for non-conductive powder and essentially no measured voltage with the conductive powder under either vacuum or ambient pressure.
posted by Maurizio Di Mauro
September 5, 2012
About once a month at Sigma Xi headquarters, we liven up the lunch hour with an American Scientist Pizza Lunch talk. In these informal lectures, scientists describe new research to nonscientists. The series is light on jargon but heavy on solid science. Each Pizza Lunch offers an in-depth look at its subject, whether it's bedbugs or the smart grid. Click below to read about and download these talks -- and to subscribe!
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