I mentioned previously the column "What Happens Next" in the issue of Physics Education journal. I am a fan of that column because I love thinking about these "mundane" problems or puzzles. We dealt with bouncing grapes in sodas last time.
This time, it is another good one from the May 2011 issue. You have a regular plastic water bottle, filled with water. You poke a hole close to the bottom of the bottle, and another hole close to the top. With both holes opened, the water will flow out of the bottom hole. You can stop that by closing the hole on top. See picture
But what will happen if you toss the bottle of water up into the air?
I'll post the answer later, because I'm sure you might want to try this out yourself! :)