What You Need:
- Blow up the balloon.
- Hold the balloon close to your ear while you tap lightly on the other side.
Although you only tap the balloon lightly, your ears can hear the noise loudly. When you blew up the balloon you forced the air molecules inside the balloon closer to each other. Because the air molecules inside the balloon are closer together, they become a better conductor of sound waves than ordinary air thus resulting in the loud tapping noise.