hello everyone so here we gonna start off with a new section and what we have in this question is we have a box okay so just a boring old box on a table now i want you to really think about this if you have a box resting on a table what kind of forces are acting on that box well imagine the table wasn't there then what would happen to the box correct it would fall so that means that there is a force of gravity okay so i'm going to call that f g so that is a force of gravity so what that means it's the force of the earth attracting the box your teacher might call fgw which stands for weight absolutely fine whichever is best for you and then if i put the table back then that doesn't mean that gravity now disappears so gravity is still acting down but if that was the only force acting on the box then the box would have to move down and so there's a force that the table is exerting on the box as well so the table is keeping the box up and we call that force a normal force and so now there are two ways to draw this these little arrows aren't correct that's just my way i'm just trying to show you something but the prop the two ways to do it would be the following so we get force diagrams and we get free body diagrams free body diagrams is the one that you're going to use most often teachers will typically explain force diagrams you'll do it for maybe a day or two and then you'll typically go over to free body diagrams so this was the original situation and so on a force diagram you draw the object like that over there then any forces acting on that object you would show like this so for example the gravity will look like that so it always comes from the center of the object then the normal force would look like this and then of course you'd always have to label it and then just always add a little key like that so it just makes it look nice and neat and it lets the examiner know that you understand what you're doing now let's do the free body diagram so with a free body diagram you literally just draw a dot and then all arrows will point away from the dot and so notice that for both of these i forgot to mention i said f g and then i also added w you only have to choose one of those okay so here we have a force diagram and a free body diagram a free body diagram you don't see the object you just see a dot with the force diagram you draw the object but that doesn't mean you have to draw the table as well just the object that we're talking about and then in both cases it's always a good idea to add a little key just to explain to the examiner or to show them that you understand what you are doing here's another object now in this one we have a box once again but now someone is pushing that box so they obviously exerting a pushing force in that direction now when you try slide something across a floor if you had to stop then that box would suddenly stop moving that is because there is a force on the floor and that is known as friction the reason for friction is that if you had to use a microscope and you had to zoom into the bottom of your box it actually looks like this it's almost impossible to have a material that is perfectly straight although it looks straight if we look at it normally but with a microscope you'd see that it looks like that now the ground is the same it also has these little imperfections or teeth and so when you push two materials upon each other those little teeth they get stuck and that is what friction is so that will always be there unless the question says ignore friction and then obviously there's always going to be gravity trying to push the object down and then there's always a normal force trying to keep the object up which is this which is the the surface trying to keep the object up because if that wasn't there then the object would just fall straight through the ground i mean we can see that the only arrow going in the vertical direction is that one and so the object would move downwards and so we're now going to put this in a force diagram and a free body diagram and so there is a force diagram so the applied force by the person we've called that f a and then friction is just ff now if your teacher draws the arrow going like this for friction that's okay guys there are so many different ways that i've seen people do this as long as you understand what you are doing that's what i'm trying to do each teacher's got their different method i don't mind what i'm trying to do is just teach you and to help you understand the way it works now with the free body diagram the arrows must always point away from the object so you don't want to see situations like this where you've got arrows going towards the object even though the person is pushing like that to the right you would rather show it like this like that over there and so that is what a free body diagram would look like it's a lot easier than the force diagram because the arrows just point away and so there we go guys we've done a small little introduction on force diagrams and free body diagrams as i said if your teacher does things slightly differently then do whatever is best for you and then another thing is free body diagrams are the most popular ones those are the ones that you want to perfect so thank you very much for watching