How to play Static Rub
- Choose a test and read the electrons or the charge on the card.
- Use Q = −n·e for what gains electrons, Q = +n·e for what loses them, and n = |Q| ÷ e, with e = 1.602 × 10⁻¹⁹ C.
- Type your prediction, with a sign for a charge, and press Start. Watch the electrons move.
- Compare the orange dashed line with the charge or the count on the right.
Electric charge
Everything is made of atoms, and every atom has positive protons in its nucleus and the same number of negative electrons around it, so it is neutral. Rubbing two different materials pulls some electrons off one and onto the other. Nothing is created: the object that gains electrons becomes negative, the one that loses them becomes just as positive, and the total charge stays 0. That is conservation of charge. Charge is measured in coulombs (C), and one electron carries e = 1.602 × 10⁻¹⁹ C, so even the 480 nC on a rubbed balloon is three million million electrons. Charge always comes in whole electrons: it is quantized. Like charges repel and unlike charges attract, which is why a rubbed balloon sticks to a wall and lifts your hair.
A focused learning model
Electrons move at a steady rate for 2 s; the dust grain gains its electrons one at a time over 3 s, and the atom's two electrons leave one after the other. Nothing else changes: the protons stay where they are and the total charge stays 0. Each mark stands for many electrons, and the objects are not to scale. Answers within 2% are right.