Answer:
Due to energy loss.
Explanation:
The law of conservation of energy states that energy can neither be created nor be destroyed. It can only change its states from one energy state to another.
The efficiency is defined as the ratio of output work to the input work. The efficiency of the fan is not 100%. Because some of the energy is lost in the form of heat and sound. No machine is 100% efficient. There is always some loss of energy takes place.