 Let's talk about forced diagrams or sometimes called free body diagrams in different books. There's a couple different ways we can create these and also once we've created them how do we construct the equations. So let's start with just basic coverage here. When I've got a free body diagram, I talk about a single object at a time. Now some books show that object as a dot. Other ones show it as just a little box. Either way you can do this, each one of these represents a single object at a time and we want to show all of the forces on that object. Now I prefer using the box and for the simple reason of if I have a system with more than one object I can very easily label whether I've got mass one or mass two right on my diagram and it's a little bit easier to keep track of than just the single dot. So if we take a look at these diagrams and we want to show the forces acting on an object, we want to make sure that we indicate all of the forces and which direction they point. Now if I were to draw a force on this particular object pulling it to the right, I would draw that arrow over there towards the right and label it perhaps force one. Some situations your forces are going to have very specific names, sometimes we just number them. Similarly, if I had a force pointing upwards I would indicate that upwards. Now the confusion comes in because sometimes we say okay I'm pushing the box from the left to the right. So people will come in and draw their arrow in that way. The difficulty with this, although it makes a nice diagram showing you what it's doing for your force diagram, is this a force that's over here on the left or is that a force that's over there on the right? So instead, even though you may be pushing it so you're behind it pushing it, we would want to draw both that force one for the person in front of it pulling and force two the person behind pushing it over here on this side because both of those forces are cooperating to move the object to the right. So we would go through and draw all of our forces on as arrows. Now if you're lucky your forces are only in the up down left right and it's just a matter of placing them around and having the appropriate arrows on there. Finally we'll get a force that acts at an angle. So we want to be able to know how to deal with that type of a force. Now it's perfectly fine to put your force in there at the angle. What some books do and it just sort of helps students keep track of what they're doing is they have that force in an angle and then they'll kind of show that what really happens is that force has two components. So if we were going to call this force 7, I'm not sure how many I've got drawn around there at this point, then we'd have the y component of force 7 and the x component of force 7. So you've got your f7 in the x direction and your f7 in the y direction to keep track of the fact that that single force has two parts. Either one of those parts is equal to f7 but they're related by trigonometry. We'll take a look at that a little bit later.