How is 'mechanical efficiency' defined?

Mechanical efficiency is defined as the ratio of useful work output to total energy input. This definition highlights the effectiveness with which a machine converts input energy into useful work. In practical terms, it measures how well a machine performs its intended task relative to the energy it consumes. A higher mechanical efficiency indicates that a larger proportion of the input energy is being utilized effectively to produce work, while less energy is wasted, often as heat or other forms of energy loss.

Understanding this concept is crucial in fields like mechanical engineering and design, as it allows engineers to gauge the performance of machines and systems, optimize their designs, and improve overall energy utilization. The other options provided do not capture the essence of mechanical efficiency: the speed of work done, energy loss as heat, or the total weight of a machine are related concepts but do not define efficiency in the context of work output versus energy input.