Question

Define the term efficiency of a machine. Why is a machine not $100\%$ efficient?

Answer 1

Efficiency is the ratio of the output work and input work multiplied by $100$. Efficiency is directly proportional to friction.

Complete step by step answer:
Before understanding efficiency few points need to be cleared. A machine is a device or an instrument which is prepared by us for making the work easier and faster. It actually enhances the effort or the amount of force applied for carrying out a certain work.
For example, if a square box has to be pushed from one place to another, more energy is required than moving the box using a dolly. It is because the friction between the box and the ground has to be overcome while pushing the box without any aided device. However using a dolly reduces the friction as rolling friction between the wheels and the ground is very less than sliding friction. The dolly serves as the machine for this work.
Thus machines are used to make work easier. It is not possible to get more work out of a machine than you have put into it. A machine always does less amount of work on an object than the person who does on the machine. The reason is a machine has to use some of the work put into it to overcome friction force. Friction is the force which opposes motion between the touching surfaces. The amount of work needed to overcome friction depends on the machine’s efficiency.
Efficiency is referred to as the percentage input work by the user and the work done or output work by the machine. The output work is always less than the input work as some amount of work is utilized to overcome friction. Therefore, efficiency is always less than $100$ percent.

Note:
The efficiency can be calculated using the following equation as
$Efficiency = \dfrac{{output{\text{ }}work}}{{input{\text{ }}work}} \times 100$.
The efficiency can be made closer to $100$ by reducing the amount of friction.