Is it static or current when you rub two rocks together?

          Static electricity happens when we pile electrons on the surface of an object and they can't get away. It can also happen if we rub electrons OFF an object. When electrons move, we call that current.

          When we rub two rocks together, if they are the right kind of rocks (quartz) and it is dark enough, we see sparks. These sparks are caused by a different effect, although it also has to do with electrons. The rock is made of crystals, and the atoms in the crystals are connected with very strong forces. When we crush or break the crystals by banging or rubbing the rocks together, we release some of that energy. The energy excites electrons in the atoms, they bounce around and as they relax back into place, they send out light. We see this light as sparks. This is called piezoelectricity.

          By the way, you can see the same thing in a very dark, like pitch black, room with Wint-O-Green Lifesavers as the sugar or flavor crystals break. (It's not polite to chew with your mouth open unless you are in the dark with Wint-0-Green Lifesavers. Then it is science!)

What causes friction?

Friction happens when things move against each other. The tiny particles that things are made of, atoms and molecules, push on the particles in something moving across it. This makes them vibrate, or wiggle, and when particles wiggle we call this heat. When something heats up, it takes energy, and the energy has to come from somewhere. (Remember that energy is neither created nor destroyed.) In this case the energy is taken from the motion of the objects, and they have to slow down.

A lot of scientists have tried hard to get rid of friction in their equipment, but sometimes friction is very useful. If there was no friction, a car or bicycle would not be able to start up or slow down. The ground, floor, or whatever you are standing on would be slipperier than ice. Pencils would have to be shaped differently or they would just slide out of your fingers, but that wouldn't matter because without friction, a pencil wouldn't make a mark on paper anyway. It is more fun to think about than to experience, I bet.