At any amusement park, there is always at least one roller coaster; its make makes the park. However when people ride it they don't actually think about how it works and the physics behind it. First of all, the first hill is the biggest in order to accumulate enough energy to get through the whole thing. And after that, gravity and the conversation of energy take the lead. Although present, the friction between the cart and the track is very little and doesn't change much. Because of this, at any point on the ride, the sum of the potential energy and kinetic energy is equal; whether going up, down or even around a loop. So the next time you ride a roller coaster think about how its all gravity after the first hill!