Up until now, we've been talking about things having a certain amount of energy and not about things gaining, losing, or changing their form of energy. We've already seen how energy can change, though. A marble at rest at the top of a ramp has a certain amount of gravitational potential energy and no kinetic energy. After you let go, and the marble reaches the bottom of the ramp, the marble has less gravitational potential energy and it has acquired some kinetic energy. Seems logical that what happened was that the gravitational potential energy transformed into kinetic energy. Energy transformations like this take place all the time. This chapter deals with keeping track of those transformations, and you'll end up with an incredibly useful principle, for among other things, building amusement parks. What better use for science?