hello grade 11s in today's video we are going to be looking at forces so this is part of the mechanic section it comes just after vectors just before Newton's Laws it's very very important that you understand forces before you understand Newton's Laws so this is going to be a quick video introducing you to the various forces that you can expect in upcoming videos I'm going to be going over the forces in more detail like normal force how to calculate it weight how to calculate it friction static and kinetic friction and how to calculate it if you don't want to miss any of this videos click the link in the description box below for my full playlist let's Jump Right In as you should know from grade n and grade 10 you get contact versus non-con forces we'll mostly be working with contact forces in this section and in Newton's laws but we do work with gravitational force or weight which is obviously a non-con force now summarize the forces in the table behind me and I've put the symbol in Brackets alongside the name of the force these symbols are very very very important we use them to label free body diagrams we use them in the equations that we write in order to answer Newton's Laws questions so you need to use the correct symbol in order to get the marks now as you can see we will be learning about quite a few contact forces we've got the normal force and the symbol is either FN or n the applied force where the symbol is f applied you may in some instances use f as your symbol how however please only use f if the question uses F so for example if they give you a box and they say that a force is acting on the box pulling it to the right and the force is f and they label it f you may label it f in your diagrams as well but please avoid shortening the word applied it's Force applied or applied force then we've got a tension force and that's the the force that acts in a rope or string where it attaches to objects I will go through all of these in more detail and we've got frictional force so we can use f for frictional force you can use FF so frictional force and here you see you got fs and FK and that's different those are different depending on the type of frictional force acting on the object so you've got static frictional force versus kinetic frictional force and we will go through the differences between those a little bit in this video and more in detail in their own video then we've got the gravitational force which is weight and you can either use W or you can use FG I sometimes use W I sometimes use FG textbooks and study guides also flip between them so please make sure that you know that they refer to the same thing okay then electrostatic force and magnetic force are forces that you will deal with and you have already dealt with in a little bit of detail and you'll deal with them in other chapters in grade 11 and in grade 12 so let's go over some of these forces briefly and remember I will go over these forces some of them in more detail in their own videos um so check out the link in the description box below it's very important to understand these forces how they work how to calculate them how to resolve them into components before you even decide to approach a Newton's law question because if you can't do the basics you can't do the more complicated stuff so our first contact force is the applied force and it says of here that it is a push or a pull force and it says here that it causes an object to accelerate it does however we can have an applied force acting on an object that is not accelerating so an object that moving at a constant velocity so for example we can have an object moving across a surface there's an applied force pulling the object to the right there's friction acting to the left and the object can be moving at a constant velocity therefore it's not accelerating but it still has an applied force acting on it so just keep that in mind and like I said it's a push or a pull Force so this image over here represents a push force and this is how you would draw the force diagram remember force diagram is like this a free body diagram is with the dots so you can see that Force applied is acting to the right because this box is being pushed to the right so in this little picture it's a a push Force but it can be a pull Force now take a look at this little diagram over here over here they are indicating that this box is being pushed to the right so the displacement will be to the right over a rough horizontal surface but the force is acting at an angle so it's a 21° angle relative to the surface that angle there says 21° if I had to draw my free body diagram which I've done for you over here we've got the normal force acting on the box remember that is this Force pushing from the surface upwards onto the object because the box is moving to the right the frictional force acts to the left we've got the weight force or the gravitational force and then look at which way the applied force is going this person is pushing down and to the right so the arrow must Point down and to the right right note how all the arrows point away from the box and if you had to do this free body diagram for Marks this would be four marks and each Arrow would be a mark on the free body diagram that you do for Marks you do not resolve the forces into their components however if I were to use this in a Newton's law question when I do this later on with you you will see that it is helpful to know how to break up or resolve the applied force into its component so for example if applied is going down and to the right so it has a horizontal component going to the right which is if applied parallel or if applied X because it's along the x axis or horizontal or parallel axis and if applied Y which is vertical or along the Y AIS or perpendicular so knowing how to break it up is important knowing how to calculate the components is important but you do not indicate the components on your free body body diagram for Marks that's an applied force really just a push or a pull then we get what we call a tension force now ATT tension force is a force in a rope or string when it's stretched and you will often see this in scenario such as this one over here where I have someone pulling this box there's tension in that rope when two objects for example A and B as you can see over here are connected by a rope or string and someone is pulling the one object and then the tension in the Rope so this over here there's tension in this rope causes the other object to therefore be pulled along as well and then finally behind me we can see a pulley situation there is tension that exists in this string over here or this rope and this rope so now let's just quickly speak about that as you can see over here we've got a tension arrow pointing to the right and a tension arrow pointing to the left that happens when we have a rope connecting two objects so if if you consider object a and object B over here connected by the string there's tension in that string there's a tension force pulling object a to the right so a tension force pulling a to the right and a tension force pulling B to the left think about it someone is holding this rope and pulling it to the right that rope between A and B is what's connecting them it's what's causing a to move to the right so obviously the tension for a will be going to the right okay that tension force is pulling a to the right but the tension force for B is actually pulling B slightly to the left and I know you might say but ma'am B is moving to the right because we're pulling it to the right yes but because it's attached to a the tension is slightly tugging it in the opposite direction okay in the same direction as the frictional force would be pulling it this is very important for when we do free body diagrams and calculates things at a latest stage then we''ve got four es exerted by a surface so I've got two forces in this instance I've got the normal force which is perpendicular to the surface and then we've got the frictional force which is parallel to the surface now you can see over here I drew a surface normal force perpendicular meaning 90° frictional force parallel so here's the surface frictional force is parallel to the surface if the object moves to the right friction opposes the motion so it acts to the left let's first quickly look at the normal force in more detail so as I mentioned it is perpendicular to the surface and I will be going over the normal force in more detail in another video so click the link in the description box below to find that video I show you how we calculate the normal force it's very very very important before we tackle Newton's questions that you know how to do this so the basics very very important but for now in this video I just want you to know know that it acts at an angle at a 90° angle perpendicular so if I tilt the surface like this the frictional force is 90° relative to the surface here's another picture that maybe shows it a little bit better we've got the normal force acting at 90° to the surface here's the surface here's the surface over here the normal force is at 90° to the surface then we've got our other uh our other Force which is exerted by a surface and that is our frictional force now I will go into this in a lot more detail in an up and cominging video but all you need to know for now is that the frictional force is the force that opposes the motion so it acts opposite so if the box is moving to the right friction goes to the left if the box is moving to the left friction goes to the right and it's always parallel to the surface and what a lot of students often get wrong is for example if the box so here's my box I'm talking about this box over here if this box is pulled at an angle so you see if appli is acting at an angle they ask me ma'am is friction at an angle or what happens to friction friction is always parallel to the surface so it doesn't matter if your Force applied is acting at all weird angles the box is moving to the right in this case there we go box is moving to the right so friction is pointing parallel to the surface to the left okay same thing with when the object is on a plane if the or slope if the object's moving up the slope friction is moving down the slope parallel to the slope in future videos in the video about friction I will go over the two different types of frictions how to calculate it what happens if we change the angle of the slope how does that affect friction so don't miss that video link in the description box and then we've got our non- contct Force which is our weight and and you of course need to know the definition for weight and weight is the gravitational force of the earth that it exerts on any object near or on its surface and the direction for weight is always straight down straight down to the Earth so once again no matter what the surface looks like so if my Surface is like this here's my object weight goes straight down to the ground straight down to the ground straight down to the Earth it doesn't it's not pendicular to the surface it's straight down to the Earth and this is the formula in order to calculate Weight mass time gravity gravitational acceleration so mass in kilog and G on Earth is 9.8 m/s per second down and that's why weight acts down again I will do a video just on weight where I show you how we resolve weight into its components this is super super important in order to answer LW questions so you don't want to miss that video I will see you all in another video remember to subscribe for more physics turn on the notification Bell so you know when I post and I can't wait to see you guys in another video bye everyone