Alright, so this isn't a typical post. It's more of a guide to some terms I'm going to be using in later posts, so if anybody gets stuck on one of these terms they can always refer back to this article. Also, if I use a term you don't understand or you hear somebody use a term you are unclear with, you can always e-mail the word(s) to me at email@example.com and I can make a follow-up guide.
Okay, so our vocabulary today is four easily confused words: mass, weight, volume, and density. The two most confused are mass and weight, and some people use them interchangeably, when in actuality they're not interchangeable. In layman's terms, mass is how much stuff there is and weight is how heavy the stuff is. For instance, if I pour equal amounts of oil and water into a bottle, they should mix together, because they have the same amount of "stuff," right? Well no, because although they have the same mass (how much of each liquid is in the bottle) the molecules of water, on a microscopic scale, are more closely packed together than the oil molecules, which are more free. Because the water has more molecules packed together, it has more weight, even though we poured equal amounts of oil and water into the bottle. So the takeaway from this is that although each liquid has the same mass in the bottle, they weigh differently, so the oil rises and the water stays at the bottom.
What about volume and density? So volume is basically how big the inside of something is. A simple hut has a relatively small volume compared to Carlos Slim's (the richest living man who makes his money off of the Mexican telephone system) mansion. Density is a bit harder to understand. If you have to read this part twice, it's okay, because I also had trouble figuring out density when I first learned about it. Here goes: Basically, density is how heavy stuff is per a volume of stuff. Confusing, right? Have you ever wondered why a muscular dude weighs more than a fat guy who has the same amount of fat as he has muscle? The answer is density. Density is how many molecules are in a certain volume. If I make two boxes of exactly the same size and take muscle and fill one of the boxes to the very top with it, and I do the same with the fat, I have two boxes of equal volume holding amounts of muscle and fat that are equivalent in mass. However, the muscle weighs more because the molecules in the muscle fibers are much more closely packed together than the fat molecules. This says that the muscle has a higher density, because the mass per volume in muscle is greater than fat, so although there's equivalent mass and volume, their weights are different. This is the same with oil and water. Oil is less dense, so if I have equal masses of oil and water, oil rises to the top. Density is measured in units of mass per units of volume, so to understand it, you have to understand the other three terms mentioned previously. So there you have it: mass, weight, volume, and density.