 Let's start with the introduction to the concept of forces. We can start by asking, what is a force? And a simple physics definition for a force could be a push or pull on an object due to its interaction with another object. It's a slightly simplified definition, but it gives us a point to start from. And then as we start looking at our equations and laws, we can clarify this a little bit. So forces have a magnitude. How hard is the push or pull? It also has direction. Which way is the push or pull? Because it has magnitude and direction, that means it's a vector quantity. If I think about my notation for it, the most common symbol used for force is a capital F. And I say the most common symbol, because as we get into some other examples, we'll see a few different ones where they use some different ones. If I express this force as a vector, remember that means I'm going to have the arrow on top of it. And that means somehow I'm talking about both the magnitude and the direction. If I have just the F, that means I'm just talking about the magnitude. Because it's a vector, I could break it down into components, in which case I have the x and the y components for that particular force. And if I'm going to use my standard equation format for a vectors, I could express that in terms of the vector force being equal to the x component of the force in the i hat direction plus the y component of the force in the j hat direction. If I've got more than one force in the same problem, I need to somehow keep those separated. One common way is to use subscripts. So for example, if I've got three different forces in the same problem, I can label them as F1, F2, and F3. Or I could use letters to separate them out, force A and force B. Another way that's common is to label them in terms of what's causing the force. So I might have an applied force, a force due to gravity, or an electric force. When I talk about my units, the standard metric scientific unit is the Newton. And we use that Newton as a capital N. So the unit for force of a capital N stands for a Newton. If I want the alternate English unit, that's a pound. And remember, the pound is abbreviated as an LB. Don't ask me why. So that wraps up our brief introduction to forces. We'll see more about how they work as we start to study Newton's laws.