And the density, the mass, the shape and the size of the particle basically determines the rate at which it moves outward, as we'll see in just a moment. So said another way, we can imagine that there's this force known as the centrifugal force that points outward and it's that force that causes it to move outward along our test tube. So we have this force due to the fluid, let's say force resistance, that basically acts on that object and it causes it to move this one. So that is what creates that centripetal acceleration and centripetal force. And so we have this other force known as the force centrifugal that basically causes it to move in the other direction. In fact, that's why this process is known as centrifugation, because it's the result of this centrifugal force.