Expansion is the principle that explains event 3-Q. dancing dimes. To get the dimes to dance we must start with cool bottles. When the bottles are brought into a warm room, they warm up, causing the air inside to expand.
Since the air has to go somewhere, it pushes the coin aside long enough escape. Then the coin plink back down. The air in the bottle warms slowly, so the coin plinks many times before the air inside finally reaches room temperature.
For the activity to work, the coin must have an air tight seal on top of the bottle. Just moisten the edge between the coin and bottle with a drop or two of water. That provides the seal.