|MadSci Network: Physics|
You're right - this is a difficult question. Unfortunately, the battery idea is not likely to work, since there is a difference between static electricity and electrical current, which is what a battery produces.Electrical charges 'want to' neutralize, which is why you get zapped by doorknobs and other metal objects when you wear vinyl-soled shoes on carpet. A static buildup can be created by rubbing objects of differing compositions together. You may be familiar with what happens when rubber and fur are rubbed together - the old 'stick the balloon to the wall' trick, or an amber rod and rabbit's fur. One solution for you to try, if you have a brush with a plastic handle, is to rub the handle with a fur strip or equivalent just before the final brushing. Another solution would be to use a piezoelectric device, like the click-button barbeque starters, to generate a negative charge in the brush, though I'm not sure of the mechanics of rigging such a device. Good question, though - millions of pet owners would surely love the kind of device you decribe.
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