* Fuel is the energy source: Gasoline or diesel fuel is the primary energy source for combustion engines. The fuel is burned, creating hot expanding gases that push the pistons and ultimately turn the wheels.
* No fuel, no power: Without fuel, there's no combustion, no energy release, and therefore no power to move the car.
* Alternative power sources: While a car cannot run on *nothing*, there are alternative power sources that *don't* use traditional gasoline or diesel:
* Electric cars: These run on electricity stored in batteries.
* Hybrid cars: These use a combination of gasoline and electricity, but can run for short distances on electricity alone.
* Hydrogen fuel cells: These convert hydrogen and oxygen into electricity, which powers the car.
So, while a car can't run *without* any energy source, it can run on sources other than gasoline or diesel.
