Types of Forces

by Patrick Ford
Was this helpful ?
Hey, guys. So in the last couple videos, we were introduced to forces and Newton's laws. But a lot of times in your problems in this chapter, you're gonna have multiple kinds or types of forces that are gonna be acting on an object. So what I want to do in this video, I want to give you a quick introduction to the five most common types of forces that you're going to see in all of your problems as chapter. All of your problems are gonna involve some combination of these five forces and then later radios. We're gonna cover them a little bit more deeply, so let's go ahead and check it out. The first one is called an Applied Force, and it's one that we've already seen before. The symbol for the Applied Force is F A. And this happens anytime you have someone or something that is directly pushing or pulling on this object, for example, I take my hand and I put it on the box, and I want to push it. Now the way that you're going to draw this arrow, we know that forces are arrows. You might be tempted to draw it like this with a force like that. But what I want you to do is remember that we're always gonna draw forces as a pull arrow that acts from the objects center. So we're gonna pick up this arrow instead of drawing it like this. We're gonna draw it from the objects center like that. So that's gonna be our applied force. And there's always gonna be enacting in the direction of your push or your pull. So I'm pushing to the rights. The arrow goes to the rights. Let's move on to the second one, which is called tension. Now the simple we use for attention is called T, and this happens anytime you have a rope or a string or a cable that's being pulled. And the way this works is that instead of you pulling your hand directly on the box, you're gonna be pulling on a rope that's attached to the box. So, for example, if I'm pulling on this rope like this and the Applied Force by F is equal to five, then what's happening is my five Newtons is actually getting transferred through the rope and acting as if we were actually acting on the box itself. So if I'm pulling on the rope with five Newtons, that five Newtons gets transferred through the rope, and it's basically as if I were actually pulling the box itself. Where the force of five Newtons, that's the tension and the tension is always going to be in the direction of the pole. And again, it always happens whenever there's some kind of a rope or string that's attached to an object. Let's move on to the third one, which is called the Weight Force. The symbol we use for the weight force is a capital W. And really, this is just the gravitational pull of the gravitational force from the Earth. You're always gonna assuming your problems, that there is a weight force unless you explicitly told that there is none, and the direction of the weight force is always going to act towards the objects towards the Earth's center or whatever planet you're on. So, for example, I have this box here. It's floating way above the surface of the earth, and so we're gonna do is we're always going to draw an arrow that acts towards the earth's center, which is right over here now, if you had a box that was on the surface, you just draw another arrow that acts towards the object center. And it doesn't matter whether the object is on the surface, inside the earth or above the earth. There's always going to be a weight force and act towards the objects, the acts towards the Earth center. So all of these forces here are the weight force. Now let's move on to our 4th and 5th force, which is called the normal. So the normal forces are fourth force, and this is really just a reaction to some kind of a surface push. It happens whenever you have two objects or two surfaces that are touching each other or in contact. So the normal force, the symbol we can use for this is called N. And really, what's going on here is you have these two surfaces that are in contact, and this box is being pushed against the surface by the weight force. Remember, we said that the box is going to have some weight force. You're always going to assume that there is one. So this box is being pushed against this table top. Whatever its surface it's lying on. And so the reaction to that surface pushes that the surface pushes back on this object and that's called the normal force. Now the direction of the normal force is always going to be perpendicular. Perpendicular means 90 degrees to the surface. So, for example, are surface. Here is the horizontal line and our normal force makes a 90 degree angle. With that are normal is always going to be perpendicular. You can also have normal forces that are horizontal not only vertical, for example, in this other example here we've got this box. I know that I have a weight force like this that acts straight down. But with this force here in my hand, it means that there is an applied force. So I haven't applied force that pushes to the right against this surface. Here we have these two surfaces that are in contact. So this is my f A. And the reaction to that surface push is that I have a normal force that pushes back against me to the left. Notice how now The vertical line is kind of like the surface, and I have this normal force that is perpendicular 90 degrees to that surface. Alright, And last but not least, we're gonna cover the friction force. The friction force is given by the simple little F and whenever it happens, whenever you have two surfaces that are in contact. But those two surfaces are rough, so every time you have to surfaces that are rubbing against each other, that's when you're going to have friction. So, for example, here we've got these two surfaces and I have them in contact. Let's say that the surfaces are rough now. The force of friction is usually going to be opposite of your direction of motion. So, for example, if I'm moving this box to the right, then that means that there is going to be a friction force of resisting force that's going to try to bring this box to a stop, and it's going to act to the left. That's how the friction force works. We're gonna cover that a little bit more deeply in a later video. That's it for this one. Guys, let's go ahead and take a look at some examples