 Now we're going to introduce two concepts called vectors and scalars. They're very closely related. So understanding the difference between these two is very important in physics. So if I look at these two quantities, they're both the description of a physical quantity, but some physical quantities, what we care about is how much of that quantity do I have. Other ones, what I care about is how much and which way. So the big difference here between scalars and vectors is what do I care about? Is it just how much or is it how much and which way? Now the how much part which both scalars and vectors have, we call the magnitude. The which way is the direction. So when we talk about vectors, we want to specify both the magnitude and the direction or how much and which way. If I've got a scalar, I really only care about the how much part. Now it's a vector. One of the ways we can describe this is using some sort of an arrow. It's a really common method of doing this and in this case, how long the arrow is is supposed to represent how much you have or your magnitude and of course, the direction is represented by which way the arrow points. To really understand this, let's give you some practical examples. Let's start with mass. I can very easily talk about how much mass do I have, but if I'm talking about how much mass does that bowling ball have, there's no direction associated with that. It's not, it's got 10 kilograms up. It's just got 10 kilograms. There's no direction involved with mass. So mass is always a scalar quantity. Now if I talk about distance, I can talk about that in a scalar sense, too. And let me give you an example here. Let's say the doctor tells you you need to walk a mile each day to be healthy. All he cares about is how far you're walking or how much distance you're walking, not which direction. He doesn't care about the direction, so distance in this sense is only a scalar quantity. Now very closely related to distance is our concept of position. But position, I do care which direction I'm in. If I'm going to tell my friend, hey, can you come pick me up, I'm 10 miles away, you better also tell them which direction you are. Otherwise they're not going to be able to find you. So here in this case, which direction is just as important as how far if you're describing your position relative to some reference point. Another example of a vector is force. Force is the pusher pull on an object. And practically speaking, yes, it matters very much how much force you use, how hard you push. But it also varies very much matters which direction I'm pushing it. You're going to get very different effects depending on which direction you push it. So that's an example where I have to care about the magnitude and the direction. So as we move through physics, you want to keep track of these differences between what's a vector and what's a scalar. In some problems, I only have to care about how much. But in other problems, I have to keep track of how much and which direction. And those are the vectors.