Charging by rubbing
Rub balloons, combs, glass rods and plastic refills, bring them near each other, and sort twelve pairs into those that attract, those that repel and those where nothing happens.
Core concept
Rubbing two materials gives them opposite charges; like charges repel, unlike charges attract, a charged object pulls uncharged bits, and earthing lets the charge flow away
Topic: Some natural phenomena
Rub a balloon on dry hair and it can pick up bits of paper or stick to a wall. Rubbing moves tiny negative charges from one material to the other, so one becomes negative and the other positive. Charges that are the same (like charges) push each other away: they repel. Opposite (unlike) charges pull together: they attract. A charged object also pulls small uncharged things. Charge cannot stay on a metal held in the hand, or on a wet object, because it flows away; joining an object to the earth (earthing) removes its charge. Lightning is a giant spark between charged clouds and the ground.
What you will learn
- Explain how rubbing charges an object.
- State that like charges repel and unlike charges attract.
- Explain earthing and why it keeps us safe.
- Link static charge to lightning.
Before you start
- Know what a force is: a push or a pull.
Materials
- Two balloons, a plastic comb, bits of paper, two plastic refills and a polythene bag
Equipment
- Two glass rods, a piece of silk and some thread to hang things
Procedure
- Pick a pair, find what charges they carry and why they behave as they do.
- Do this for at least eight pairs.
- Sort every pair: attract, repel or nothing happens.