Rub each balloon on the sweater, so that they each have negative charges on them. Place one balloon as far away from the sweater as possible on the right. Then bring the other balloon close to that balloon. What happens and why?
When the balloons are rubbed on the sweater, some of the electrons from the sweater transfer to the balloons. This causes the balloons to have a surplus of electrons, giving them a negative charge.
When one balloon is placed far away from the sweater on the right, it maintains its negative charge.
However, when the other balloon is brought close to the first balloon, they will be attracted to each other. This is because objects with opposite charges, in this case, negatively charged balloons and a positively charged sweater, attract each other.
The reason behind this attraction is the basic principle of electrostatics, specifically Coulomb's Law. According to this law, opposite charges attract each other while similar charges repel.
Therefore, when the negatively charged balloon is brought close to the positively charged balloon (sweater), there is an attractive force between them, causing them to move towards each other.