 Welcome to Physics in Unity with Jonathan Bradley, Head of Studios and Innovative Technologies. I want to talk to you a moment about physics in the world. So if we take an object and we add it to our world, say we take a simple sphere and drop it in, that object, while it exists and we have a way of viewing it, doesn't understand the physics of this world just yet. If we were to start our game, this object would just float. It doesn't know that gravity exists and it doesn't understand that it should react in that way and it doesn't really respond to any sort of physical interaction that would knock it somewhere or tell it to behave in a certain way. What we do is we add a thing called a rigid body to that object, which gives it a sense of the physics of the world. We can check that we want it to pay attention to gravity, in which case, as we start the game, the ball falls and it rolls and it behaves as you would expect a ball to behave. So if you have slanted terrain, it will roll to the lowest portion of that. Or if it's flat, it may bounce a couple of times and stay still. The important thing to remember here is that adding objects to the world doesn't necessarily make them behave like an object in the real world would. We have to actually add that functionality ourselves.