A heat engine is a mechanism in thermodynamics and engineering that transforms heat to mechanical energy, which may subsequently be utilized to do mechanical labor. Furthermore, some energy is lost due to friction and drag. The overall process is called thermal efficiency. A machine that does not lose any energy is called a heat pump. The most common type of heat engine is the internal combustion engine. It converts the chemical energy stored in fuel molecules into mechanical power output through the action of explosions. The resulting piston movements turn a crankshaft, which provides power to various parts of the vehicle via a drivetrain. Some vehicles use electric motors instead. Electric motors use electricity from external sources or from an on-board battery to provide all-electric operation. Other types of heat engines include gas turbines, steam engines, and solar panels/wind turbines. These are used in different applications such as electricity generation, water pumping, and transportation. Gasoline engines operate using compression ignition. This means that when gasoline is poured into the tank, it comes in contact with air at room temperature. Because oxygen atoms are more electrically positive, they will attract electrons from the carbon-hydrogen bonds in gasoline molecules. This makes the gasoline less reactive and prevents it from exploding before it reaches its ignition point. The gasoline then self-ignites when it gets hot enough from running through the engine.