Static Shock
Rub a balloon on someone's hair and strange things happen. Drag the balloon to rub it, then see what it can do.
- Balloon charge
- −0 nC
- Extra electrons
- 0
- Hair charge
- +0 nC
- Balloon voltage
- 0.0 kV
The maths, live
Number of electrons n = q ÷ en = 0 nC ÷ 1.6 × 10⁻¹⁹ C = 0Coulomb's law F = k × q₁ × q₂ ÷ r²F = 8.99 × 10⁹ × 0 nC × 0 nC ÷ (44 cm)² = 0.00 mNSpark when gap < V ÷ 3 kV per mm0.0 kV ÷ 3 = 0.0 mmRub the balloon on the hair, then move it away and back. Is the pull stronger when it is closer? Try sticking it to the wall, picking up paper and touching the doorknob.
How it works
Rubbing moves tiny electrons from one material to another. Hair and wool lose electrons easily and rubber gains them, so the balloon becomes negatively charged (−) and the hair is left positively charged (+). Opposite charges attract and like charges repel, which is why each charged hair pushes away from the others and stands up.
The force between charges follows Coulomb's law, F = k × q₁ × q₂ ÷ r². Halve the distance and the force is four times bigger. A charged balloon can even pull on things with no overall charge, like a wall or bits of paper, by pulling their charges slightly towards it. With enough charge, the air near a metal doorknob breaks down and the charge jumps across as a spark.
Try this
- Rub the balloon on the hair, then bring it close and move it away. When is the pull strongest?
- How much charge do you need before the balloon sticks to the wall?
- Switch to damp air. Why do static shocks happen more in dry winter weather?