 Now let's look at the equation for static friction. So static friction is a case where you've got two solid surfaces in contact, and you're trying to move between those two surfaces, so you're trying to move one surface across the other. But the objects don't slide relative to each other, so you're attempting motion but you're not succeeding at moving things. In other words, the static friction makes them stick together. Well the equation that represents that is given here. Now over here on the left hand side we have our frictional force. Now the way our textbook uses this, it's a lowercase f with a subscript of an s. Some books do have an uppercase f, but we're using a lowercase f. Over here on the other side we've got the normal force, so that f sub n is your normal force. This is our coefficient of static friction, and that's the Greek symbol mu, and because it's static friction it has the subscript of an s. We've got another video for talking more about that coefficient. The last thing I want to point out about this equation is that the symbol in the middle here is not an equal sign, but a less than or equal sign. So we want to explain that. We're not used to having inequalities in our equations here. So less than or equal. The force of static friction is only going to be as much force as needed to hold it still. And that means if you're attempting to push it but you're only pushing a little bit, it only needs a little bit of friction to hold it still. If you push a little harder, then the friction has to increase to keep it from moving. Well there's a maximum, and that maximum is when it actually equals mu sub f f n. So up here you're going to have less than mu sub f n, but here there's a maximum amount that you can push. If you push too hard, more than that maximum amount, then friction can't hold it still and you do not have static friction anymore, because static friction has to hold it still. So there's a maximum amount that we can have, but anything else you're going to have less than that maximum. So this is our introduction to static friction. We're still going to need to see some worked examples before you really get this.