We have some basic equipment we can use for some simple experiments. We have two clear nylon rods, two black rubber rods, some pieces of material, and a rotating stand.

First place one nylon rod on the rotating stand and bring the other rod close to it. What do you observe?

Now repeat after rubbing both rods with a piece of silk.

How can we explain these observations?

We could come up with a simple model to explain what we saw. Maybe rubbing a nylon rod with silk transfers something between the rod and silk. When the two rods have both experienced the same transfer they repel one another.

Repeat with the two rubber rods, first without rubbing the rods and then after rubbing the two rods with felt or fur.

Does what we observe fit with the model we came up with above?

Now repeat but with one nylon rod rubbed with silk and one rubber rod rubbed with fur or felt. Does what we observe here match our model?

Let's come up with a name for the thing that gets transferred between a rod and the material it was rubbed with.

We can call it charge. If you want to be really specific, you could call the tiny objects that get transferred, and that carry the charge, electrons.

When a nylon rod is rubbed with silk electrons are transferred from the rod to the silk, leaving the rod positively charged. Two positively charged objects repel.

When a rubber rod is rubbed with fur or felt electrons are transferred from the material to the rod, giving the rod a negative charge. Two negatively charged objects repel.

When a positively charged object is brought near a negatively charged object the two objects attract one another.