Vibrating balloon

1. Hold a balloon in your hand and ask your friend to shout “ouuu” in a loud voice.

What happens?
Why do you think it happens?

                                                                                                                               Image 3.5: Vibrating balloon

2. Is it due to the air that comes from your friend's mouth? Hold a paper or a notebook between the balloon and your friend's mouth to block the air. Now ask your friend to shout again.

Do you still feel the vibrations?

3. Take two steps away from your friend. Ask him to shout.

Does the balloon still vibrate?