Right, so most of you are seeing Newton's cradle, one goes in, one comes out, because momentum is conserved and also energy. You can't get one in and two out. Why when you lift two out, does two go in and two go out? Why don't you ever get one going in and two going out? Surely if momentum is conserved, mass times velocity, then you must be able to sort of have twice the velocity on one side and you could have half the velocity and twice the mass going out the other side. The reason it doesn't is because energy has to be conserved as well. And energy is half mv squared, so that ties you into making it so that both of those work. The only reason that it works is because these are elastic collisions. In elastic collisions, energy is conserved. And so you can do the normal things you do with Newton's cradle, you can have three in, you can have three coming out. You can see it's not perfect because in the end they all start moving. But basically that's a model of elastic collision. This one however, is an inelastic collision. This one, even though they're all set up pretty similar and I got my lab assistant to do them, I made a different material. This is lead, solid lead. One goes in, two, three, four, five comes out. There must be some energy loss. Momentum still conserved because we have an inelastic collision, but the energy is not conserved. So the energy has been lost in this situation. So here we have an elastic collision, here we have an inelastic collision with the Newton's cradle, energy and momentum is conserved with our lead balls, only momentum is conserved and not the energy. So that one just feels wrong, doesn't it? You just do that and it goes there.