Charging Problems
When you rub a glass rod on a balloon, electrons move from rod to balloon. The more you rub, the more electrons move over. The rod and balloon can gain quite a lot of charge.
The positive charge on the rod would attract the negative charge on the balloon. Move the rod closer to the balloon, and this attraction would get stronger. Move it until the rod nearly touches the balloon.
This force becomes very strong - strong enough to pull the electrons out from the balloon. The electron leaps across the gap to the rod. This is a spark.
In everyday life, things often get rubbed against each other. The resulting sparks can range from mildly irritating to very dangerous.
When I put on my shirt, or when I touch the dress of another person, I sometimes feel a sharp pain, like I am pricked by a needle. This happens when the dress and my hand gained a lot of opposite charges. When they touch, a spark leaps across and cause a sharp pain. Usually, these are very small sparks that you cannot see.
When a car runs along, friction between tyres and road surface causes the car body to charge up. When the car stops at a petrol station to refuel, there would be petrol fume in the air. If a spark leaps from car body to the petrol pipe, the petrol station will explode.
The most amazing spark of all happens when friction between cloud and air causes the cloud to charge up. The charges build up to a tremendous voltage in the clouds. Then giant, spectacular sparks leap from clouds to ground. This is how we get lightning.