Answer:
It uses graivity and momentum because since we all know, gravity pulls things down, they have a chaint hat lifts the carts up, and then when it gets to a top, it releases it. When it goes down very high, it will go faster. Then it uses momentum when it goes up, then down again, or a loop to regain speed. IT doesn't need a engine or a motor to speed it up or slow it down because gravity and momentum is already doing the job a engine could. Like I said, when it is high in the sky and released, it goes down in incredible speed. And when it needs more speed to keep the ride going, it can add a loop or tight turns to increase it more.
