One day, Bob and Hannah were sitting out on their deck, sipping on some drinks. Bob ran into the house, got an empty two-litre bottle from the freezer and a quarter, and returned to the deck.
“I bet you money that this quarter will move with nobody touching it.”
Hannah thought this was a sure win; however, she lost. When Bob placed the quarter on the mouth of the bottle, the quarter began jumping on one side and making popping sounds.
How did Hannah lose?
Answer
As the bottle had previously been in the freezer, the cool air inside expanded when placed in a warmer temperature and escaped through the only out, or the mouth. However, while the quarter was blocking this passage way, the cool air could not leave. Therefore, the expanding cold air moved the quarter enough so that a little cool air might come out of the bottle. The popping sounds were from the quarter landing back on the bottle.