What is an engine commonly defined as?

An engine is commonly defined as a machine designed to convert energy into useful mechanical motion. This definition accurately captures the primary function of an engine, which is to take energy from a fuel source, such as gasoline or diesel, and convert it into kinetic energy that can be used to perform work, such as moving a vehicle or powering machinery.

Engines typically operate by burning fuel to create combustion, which generates energy that is harnessed to produce motion. This conversion process can involve various mechanisms, such as pistons, turbines, or rotary motion, depending on the type of engine. The emphasis on transforming energy into motion highlights the core purpose of an engine—production of mechanical work.

This definition is distinct from other choices that do not fully encapsulate the engine's function. For example, the option about storing mechanical energy emphasizes preservation rather than conversion, while the description of a machine that converts fuel into heat is more aligned with a furnace or boiler. The choice regarding a system for transmitting power describes components like gears or belts that may be used in conjunction with an engine but do not define an engine itself.