A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be transformed, by a connecting rod and crank, into rotational force for work. The term "steam engine" is most commonly applied to reciprocating engines as just described, although some authorities have also referred to the steam turbine and devices such as Hero's aeolipile as "steam engines". The essential feature of steam engines is that they are external combustion engines, where the working fluid is separated from the combustion products. The ideal thermodynamic cycle used to analyze this process is called the Rankine cycle. In general usage, the term steam engine can refer to either complete steam plants, such as railway steam locomotives and portable engines, or may refer to the piston or turbine machinery alone, as in the beam engine and stationary steam engine.
A model of a beam engine featuring James Watt's parallel linkage for double action
A mill engine from Stott Park Bobbin Mill, Cumbria, England
A steam locomotive from East Germany. This class of engine was built in 1942–1950 and operated until 1988.
A steam ploughing engine by Kemna
In physics, work is the energy transferred to or from an object via the application of force along a displacement. In its simplest form, for a constant force aligned with the direction of motion, the work equals the product of the force strength and the distance traveled. A force is said to do positive work if it has a component in the direction of the displacement of the point of application. A force does negative work if it has a component opposite to the direction of the displacement at the point of application of the force.
A baseball pitcher does positive work on the ball by applying a force to it over the distance it moves while in his grip.
Lotus type 119B gravity racer at Lotus 60th celebration
Gravity racing championship in Campos Novos, Santa Catarina, Brazil, 8 September 2010