For a non-idealized roller
coaster system, not all of the energy is conserved. Friction is the main cause of energy leaks in the system and the
reason why mechanical energy is not fully conserved for a real roller
coaster. This is because friction is a
nonconservative force. Nonconservative
forces are forces that cause a change in total mechanical energy. Friction opposes motion by working in the
opposite direction. The friction
between the train and its tracks as well as between the train and the air take
energy out of the system, slowing the train and creating both heat and
sound. This effect is most noticeable
at the end of the ride as all remaining kinetic energy is taken out of the
system though brakes. Because of the
energy leaks due to friction, each successive hill or loop on a roller coaster
must be shorter than all the hills or loops previous to it, otherwise the train
will not have enough energy to make it all the way over.