Efficiency

Real World Example

Imagine trying to pour a full cup of coffee into a travel mug but noticing that some spills over the sides and doesn't make it into the mug. This situation is similar to how a machine converts energy input into work output because not all the energy put into the machine is used efficiently to do work—some is "spilled" or lost, like the coffee. Just as the travel mug only holds a certain percentage of the coffee you pour due to spillage, the efficiency of a machine is the percentage of energy input that successfully gets converted into useful work, with the rest lost to heat or friction.