The common plastic water bottle makes a useful container for demonstrating properties of gases and liquids. As typical examples, we know that "air" is a gas (made up of nitrogen, oxygen, water vapor, ozone, carbon dioxide, and several "trace" gases) and water is a liquid. We should also note that gases and liquids are both "fluids". That is, they can flow or change shape, rather than having a fixed shape like a solid.

In the state of Maryland, a local politician claimed that sea level is rising because there are too many people putting boats on the open ocean! This is a true story! Is this or similar claims possible? Imagine if all of the people in the world agreed to go float on the ocean at the same time! Could that result in a significant sea level rise, perhaps even destroy low-lying nations such as Bangladesh?