Why did me need to have the same molecules in each bottle? and what would have happened if we didn't use the same molecules?


Background info: We learned about molecules and how when a object is heated the air becomes less dense and the molecules is the opposite since they don't spread out and become more dense. What I mean with this question is in class we experimented by putting a bubble on a bottle and putting it on a hot water, the water made the molecules inside less dense and the bubble went up but when we tried cold water the bubble went down.