Final answer:
Rubbing two balloons on your hair transfers electrons, charging them negatively through static electricity. Charged balloons repel each other because like charges repel. Polarization can also cause a charged balloon to stick to a neutral surface.
Step-by-step explanation:
Static Electricity and Balloons
When you rub two balloons on your hair and hold them by their knots, you are transferring electrons from your hair to the balloons, giving the balloons a negative charge. This process is known as triboelectric charging, which is a type of static electricity. Subsequently, when you hold the charged balloons close to each other, they will repel each other because like charges repel. This phenomenon can be observed in a PhET Interactive Simulation about balloons and static electricity, which helps visualize how charged objects interact.
An additional concept related to charged balloons is polarization. If you bring a charged balloon near a neutral surface, like a wall, the charges within the wall will rearrange themselves in response to the balloon's electric field (even though the wall remains overall neutral), resulting in the balloon sticking to the wall. Experiments and simulations like the PhET Explorations can make these concepts more concrete and illustrate the principles of static electricity in action.