 Now let's talk about mass. When we look at measurements of mass, we want to keep in mind its dimensions and its units. Again, dimension is what type of measurement you're making. And so mass is one of the standard ones, and any type of measurement of mass has that same basic dimension. And our generic notation for the dimension is a capital M. When it comes to units of mass, any particular measurement has the value, the number, but it also has the units. So what are some of the units that are available when we're measuring mass? Well, here's a list of a few of them. Kilograms, grams, milligrams, those are probably ones that you're well familiar with. The metric ton is another one. Amu is the atomic mass unit. That's a very small mass that are used for measuring individual atoms and molecules. And then you got the slugs. Now slugs is not used very commonly anymore, but that's the old English unit that was used for measuring mass. In our standard system, we're going to have kilogram as our basic unit that we're going to use as our standard. One of the things you have to be careful with when it comes to mass is confusing it with weight. Now in our physics course, we're going to study this in more detail so you can understand why there's a difference between mass and weight, but they're not the same things. It often gets confusing because we use them as if they're interchangeable. So example, the metric unit of kilogram and the English unit of a pound. Well, kilogram is a mass, but a pound is actually a weight, so they're not the same thing. So be very, very careful as you're going through to keep track of what's a mass and what's a weight.