More Experiments

A soda can is an excellent charge detector. If we bring a positively charged nylon rod close to the can, the can is attracted to the rod.

What happens when a negatively charged rubber rod is brought close to the can instead?

  1. nothing
  2. the can is attracted to the rod
  3. the can is repelled by the rod

In both cases the can is attracted. Whether the rod is positive or negative, the rod polarizes the can so the side of the can closest to the rod has a charge opposite to the charge on the rod. This leads to a net attractive force between the can and the rod.

The same kind of thing happens with a stream of water. The stream is attracted by a charged rod because of the net attractive force from the way the water is polarized when the rod is brought near it.

Here's another experiment. Take a charged van der Graaff generator and bring a metal ball close to it. The ball is attracted by the van der Graaff, touches it, and is then repelled. How can we explain this?