 Now let's talk about tension forces. We've got a tension force. It's going to be given with a symbol often of F sub t. Although sometimes we use just a capital T in some books. These happen whenever you've got a force applied indirectly on an object by pulling on a rope, chain, cable, etc. attached to the object. So what does that mean really? Okay, so I've got an object. And I want to pull on it, but I'm not pulling directly on the box. Instead, I'm pulling on some sort of rope that's attached to that box. And it could be a rope. It could be called a cable. It could be called a chain, any of those things. Now when this happens, as you pull on the rope, that rope is going to tighten up causing the tension. So I've got my box here. I pull on my hand, which pulls on the rope, which then the rope pulls on the object creating my force of tension. So if I've got an ideal rope, and that's what we use most of the time in general physics, it doesn't stretch. It's also not stiff. That means you can't push on the rope and get the object to move. You can only pull on the rope to get the object to move. And that rope has to have much less mass than the attached object. Again, in general physics, we're typically using ideal ropes. And that means we've got the same tension through the whole rope. So what if we have a rope between two objects? So it's not my hand is pulling on the rope. So I've got two objects and there's a rope between them. Maybe I'm pulling on one of the objects. Well, in that case, I've got the same tension at both ends. And so there's a force pulling to the right on this box and pulling to the left on that box. And those two forces are exactly equal because I have the same force of tension everywhere along that rope. What if I've got a connection point? You know, more than one rope comes together. Well, when those ropes connect, each section can have a different tension. That doesn't mean they have to have a different tension, but they can. So my tension along each one of these segments would have a different value or it could potentially have a different value. Now last, I want to talk about tension and pulleys. So a rope can be redirected by a pulley. But if it's an ideal pulley, it doesn't change the tension. And an ideal pulley, it's pretty much one that doesn't have any friction as the rope passes over it. So here's an example where I've got one object sitting on a table and the rope comes out and goes over some sort of pulley and then there's an object hanging down off of it. This tension over here pulling on this box and this tension here on this box are exactly the same tension. Another one of the classic physics experiments, sometimes called an at-wood machine, I've got two objects both connected to a rope which is hanging over a pulley. And again, the tension on both sides here has to be equal to each other. So that's a brief explanation of tension forces.