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The balloon sticks to the wall because of the phenomenon known as electrostatic attraction. When the balloon is rubbed against the sweater, it gains negative charges, creating an imbalance of charges on its surface. The wall, on the other hand, is neutral, meaning it has an equal number of positive and negative charges.
When the balloon comes close to the wall, the negative charges on the balloon repel the negative charges in the wall, causing the negative charges in the wall to move away from the balloon. This creates a region of the wall where there is a relatively higher concentration of positive charges compared to negative charges.
Opposite charges attract each other, so the positively charged region of the wall is attracted to the negatively charged balloon. This electrostatic attraction causes the balloon to stick to the wall.
It is important to note that this is a temporary effect and the balloon will eventually lose its charge and fall off the wall.