Why can’t a real machine ever have 100% efficiency?

Machines are not 100% efficient because some of the work done by a machine is used to overcome friction. So work output is always less than work input. Work: Done by machines is calculates as Mechanical Efficiency which is Work Output divided by Work Input.Click to see full answer. Then, why is a machine not 100% efficient?Explanation: No machine is free from the effects of gravity, and even with wonderful lubrication, friction always exists. The energy a machine produces is always less than the energy put into it (energy input). That is why 100% efficiency in machines shall not be possible.Subsequently, question is, is it possible to design a machine that has an efficiency greater than 100 %? In other words, no machine can be more than 100% efficient. Machines cannot multiply energy or work input. If a machine were 100% efficient then it can’t have any energy losses to friction, so no friction can be present. In that case the theoretical and actual mechanical advantages would be equal. Keeping this in view, can machines be 100% efficient? The short answer is: It can’t. Almost all machines require energy to offset the effects of gravity, friction, and air/wind resistance. Thus, no machine can continually operate at 100 percent efficiency.Is Carnot engine 100 efficient?No,, never . It can be 100℅ only if the sink temperature is zero or the source temperature is infinite (very large value). Carnot is an ideal cycle is provides benchmark to compare efficiency of other cycles. Carnot efficiency is the maximum efficiency that can be achieved in a cycle.