Consider the following scenario. A car for which friction is not negligible accelerates from rest down a hill, running out of gasoline after a short distance (see below). The driver lets the car coast farther down the hill, then up and over a small crest. He then coasts down that hill into a gas station, where he brakes to a stop and fills the tank with gasoline. Identify the forms of energy the car has, and how they are changed and transferred in this series of events.

1 part at the top of the hill the car has gravitational potential energy, which is transformed in a part into kinetic energy and another part into heat by the work of the friction force that opposes the movement.

2 part when the other hill rises it loses kinetic energy that is transformed into gravitational potential energy and part in heat due to the work of the friction force on this hill.

3rd part in the last descent all the gravitational potential energy is transformed into kinetic energy and the application of the brakes is transformed into heat due to the negative lock of the friction force and filled with gasoline that has chemical energy that can be transformed in the engine.