Mechanical efficiency

In physics, mechanical efficiency is the effectiveness of a machine and is defined as

{\text{Mechanical Efficiency}}={\frac {\text{Work output}}{\text{Ideal Work output}}}

Mechanical efficiency is a ratio of actual work output to Ideal work output. Where the Ideal work output is the work input. It is often expressed as a percentage. While the efficiency of an ideal machine is 100 percent, an actual machine's efficiency will always be less than 100% because of the second law of thermodynamics, which states that the quality of energy will decay, eventually becoming heat. This means that some of the work put into the system is transformed (lost) into thermal energy (heat). In a mechanical system, friction is the most common means by which work is lost to heat.

The actual mechanical advantage of a system is always less than the ideal mechanical advantage due to these losses. Another way to express mechanical efficiency is it is the ratio of actual mechanical advantage to ideal mechanical advantage.

Creating a perpetual motion machine of the third kind would require 100 percent mechanical efficiency. By recycling the work output back to the work input, a perpetual motion machine could maintain its movement forever. In controlled environments, low friction mechanisms can come close to the ideal efficiency. However, to maintain a perfectly ideal mechanism, the temperature output must be the absolute zero, which is impossible to reach due to the third law of thermodynamics. Therefore, perfect mechanical efficiency can never be achieved.

See also