In the history of physics, the concept of entropy developed in response to the observation that a certain amount of functional energy released from combustion reactions is always lost to dissipation or friction and is thus not transformed into useful work. Early heat-powered engines such as Thomas Savery's (1698), the Newcomen engine (1712) and Nicolas-Joseph Cugnot's steam tricycle (1769) were inefficient, converting about 0.5% of the input energy into useful work output. Over the next two centuries, physicists investigated this puzzle of lost energy; the result was the concept of entropy.