 This video is going to be an introduction to linear momentum. First of all, what is momentum? Momentum, which we usually use the letter p, is defined as the linear inertia times the velocity. The linear inertia turns out to be just the mass of an object. I'm thinking of momentum as a measure of the magnitude of motion in a certain direction or the tendency of an object or a system of objects to continue traveling in a certain direction. Linear momentum follows law of conservation. I've done other videos on conservation laws, especially on energy, so if it's a long time that you have been talking about conservation of energy, please look at this video right now and then come back here a few minutes later. Now, what do all laws of conservation follow? They say that what you have at the end, final, is what you had at the beginning plus the change. Now, in the case of linear momentum, what you have at the end is your final momentum. What you had at the beginning is your initial momentum and the change is through this thing that we call impulse. So impulse, how can we change how an object is moving? It's through forces. The longer a force is moving, the more change you will have. So this impulse is defined as the force acting on the object times the time. And that's the basics of conservation of linear momentum. What is it usually used for? It's used for collisions or explosions. I'm going to do more videos on that a bit later on. Just one little particularity. Contrary to conservation of energy, this is a vector law. That means you actually get an equation in each direction you're considering. You can have this in x direction, y direction and z direction.