Why when you give manual cars a push they will start?

Most of the electrical energy needed to start a car is used by the starter. In fact, very little electrical energy is needed to produce a spark and fire the injectors. Usually an alternator can produce enough energy, even at low RPM, to provide power to ignition, computer and fuel pump. The total amperage of those devices may amount to anywhere between 1 and 5 amps. A typical starter can require anywhere from 75 to 200 amps, depending on the engine and starter condition. Pushing a vehicle with a manual transmission allows the engine to turn, replacing the function of the starter.