Could you please explain density? What is it? What is the concept of D = M over V?
Density is how much mass a material has for a given volume. Think about a sponge. Most artificial sponges today are made of a foamed plastic. Assume you have a one pound sponge. If you melt it down to a plastic soup with all the bubbles gone, it will be much smaller, but it will still weigh one pound. It is now denser. We use water as sort of a standard for density. We say water has a density of 1. If something weighs twice as much as the same volume of water we say its density is two. This is really handy for figuring out all sorts of things like if something will float or not. Anything that has a density less than 1 floats. Anything that has a density higher than 1 sinks. Ice is ~12% less dense than water so ice floats. Water gets bigger when it freezes so ice is less dense than water. It's a good thing too since life probably would not exist if that were not the case. A U.S. air craft carrier weighs more than 200,000,000 pounds, but I know its density is still less than one. I know this without even asking anyone since I have seen them floating.
Brian Kross, Chief Detector Engineer (Other answers by Brian Kross)