An empty bottle with a long neck (A wine bottle works well)
Piece of any kind of paper.
Breath (good breath optional)
1. Crumple up a small piece of paper so that it can easily go into and out of the bottle.
2. Hold the bottle on its side and put the paper ball an inch or so into the neck of the bottle.
3. Now, try to blow the wad of paper into the bottle.
Sounds easy doesn't it? Believe it or not, it's almost impossible. In fact, you may have found that not only does the paper ball not go into the bottle, it pops back out! The reason for this, is that the bottle is not really empty. What's in the bottle...air. That bottle is full to the brim with air. When you try to blow more air into the bottle, it doesn't go in because the bottle is already full. It's like trying to put water into a bottle that's already full of water. It doesn't work. You may be asking, why does it pop back out? That's a good question. I'm not sure, but I think it pops out because air is a little squishy. So when you blow into the bottle the air squishes a bit. Then when you stop blowing the air unsquishes and blows the paper out of the bottle.