I know air conditioners use a significant amount of energy, but turning the fan on high uses a fairly negligible amount. This started me thinking about the engine of the car. Where do most of the losses occur? I know any time you have an energy conversion or transfer, you will be losing some energy. Which of these are most significant? For example, is it heat loss in the combustion? Friction on the road? Internal friction? I don't know much about how engines work, but am curious to understand the energy involved.