Moving people and goods from place to place is a vital part of any civilization. At the beginning of the 19th century, the steam engine became powerful enough to be given wheels and take its energy source of coal with it. By the end of the 19th century, the internal combustion engine had been invented. It made use of the energy released by rapidly burning fuel inside its cylinders, making motor vehicles possible. All the energy that a car uses to accelerate and keep moving comes from the gasoline or diesel fuel it burns in its engine. A typical “fuel-efficient” car will use about 1.3 gal of fuel on a 60-mile journey. This means that about 240 million J of energy is obtained from the fuel. Only about one-third of the energy obtained from the fuel turns the wheels. Some cars can produce 100 “horsepower”. One horsepower is about 746 W (746 J/sec), which is approximately the power that a horse can develop in pulling a load.