| MadSci Network: Physics |
Hi Johnnie!
First of all, you should avoid cotton as a belt for your VandeGraaff
machine.
Cotton absorbs moisture from the air, and it doesn't perform well
as an insulator except when the humidity is extremely low. Use
rubber or plastic for your VDG belt. If you want to experiment with
cotton anyway, try wrapping it around one of the VDG rollers and
as your VDG is running, bake the roller dry with a hair dryer.
In this Triboelectric series from the book NATURE'S ELECTRICITY, cotton is labled as zero (as neither negative nor positive.)
http://www.amasci.com/emotor/tribo.txtThis is a bit misleading, because contact electrification always occurs between TWO materials. How can a single material be positive or negative? It cannot. If you touch dry cotton cloth against fur or hair, the cotton will become negatively electrified. But if you touch the same piece of cotton to teflon plastic, the cotton will become positive. The polarity of the imbalanced charge is relative, so there really is no "zero" point in the triboelectric series.
http://www.amasci.com/emotor/vdg.html
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