Answer:
Friction
Explanation:
The efficiency of a machine depends upon the percentage ratio of output work to the input work. More the difference between the input and output work, lesser will be the efficiency of the machine. In real machines, the output is always less than the input because a lot of work is consumed against friction, resulting in reduced output.
The formula for efficiency is:
Efficiency= ( Output work/Input work) x 100%
Since the output will always be lesser than the input, the ratio of output/input will always be lesser than 1 and, therefore, the efficiency will always be lesser than 100%
