Charging of Solids
Hang a balloon on a piece of thread and rub it with a glass rod. After that, the rod and balloon attract each other.
The explanation is that the rod gains something called a positive charge, while the balloon gains something called a negative charge. These opposite charges then attract each other.
But what are these positive and negative charges?
Each atom is made up of electrons around a nucleus at the centre. The electrons are negatively charged, whereas the nucleus is positively charged. Together, the positive and negative charges balance out exactly, so the overall charge is zero.
When the rod is rubbed on the balloon, some electrons from the rod go over to the balloon. The balloon gets an excess of electrons and becomes negatively charged.
The rod is now short of electrons. These are not enough to balance the positive charges in the nuclei, so the overall charge of the rod is now positive.