On a Roll
Enrichment Activity for 5-11 11-14
- Level Elementary
What you need
- A balloon
- An empty pop can (aluminium cans are best)
- Tell your friend you can make the can roll along without touching it or blowing it
- Place the can on its side on a flat surface
- Rub the balloon really fast against your hair or a woolly jumper
- Hold the balloon close to the can - the can will start moving towards the balloon
- Slowly move the balloon away from the can and the can will follow it
Results and Explanation
When you rub the balloon against your hair, electrons are transferred from your hair to the surface of the balloon, so that it becomes negatively charged.
When you hold the balloon close to the can the negative charge causes the electrons in the can to move away (they are repulsed by the negative charge, because they are negatively charged themselves). This creates a positive charge on the surface of the can, so that now the can is attracted towards the negative charge on the balloon.
This trick works well with a pop can because it's light, so it will move with a small force applied to it, and because in a metal it is easier for electrons to move around.