1, put the balloon in the bottle, and put the open end on the bottle mouth to wrap the bottle mouth.

2. Take a deep breath and blow the balloon hard. No matter how hard you try at this time, you can't blow up the balloon.

Then poke a small hole in the bottom of the bottle with a tack.

4. After taking a deep breath, blow the balloon and it will blow up.

5. When the balloon is still inflated, cover the small hole at the bottom of the bottle with your finger and the balloon will remain inflated!

If you take your finger out of the hole in the bottle, the balloon will deflate.

7. Now let's make water polo! Blow the balloon according to steps 4 and 5, and then cover the small hole at the bottom of the bottle with adhesive tape to keep the balloon inflated.

8. Fill the inflated balloon with water and tie a knot, and the balloon will fall to the bottom of the bottle. This makes a water polo in the bottle.

9. Then tear the tape from the small hole in the bottom of the bottle (the balloon is not sealed) and the water will gush out like a fountain.

Principle of self-made small fountain

An empty bottle is actually full of air. Before you poke a small hole in the bottom of the bottle, the air can only escape through the bottle mouth. Once the bottle mouth is covered by a balloon, the air will be trapped in the bottle. The closed gas in the bottle will exert pressure on the balloon, and the pressure will increase with the increase of the balloon volume, so it will hinder the balloon from increasing, that is to say, the balloon in the bottle will never blow up.