[quote author=leeyiren link=topic=1965.msg7287#msg7287 date=1285751193]
you mean there is such thing as -1C? but I thought coulomb is like kg, no -ve.
[/quote]
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1918.0
yes.
charge has + and - types.
electrons is negatively charges


we have no evidence of the existence of negative mass in the real life but in quantum physics world, things the size of atoms, there is something called anti-mass. but that is another story ;)