Question

What do you need to know to calculate the efficiency of a machine?

Answer 1

The efficiency formula is a step to calculate the efficiency of the processes and machines. It is expressed as the ratio of output to the input. The efficiency of a machine that uses energy is calculated as the useful energy yield by the machine compared to the energy used. Energy efficiency is always below $100 \%$ as machines always create some waste, such as the heat generated by an engine.

Complete answer:
Machines are tools in which work can be done easier or more conveniently. A machine can elevate loads with a small force, change the force's direction, increase the work rate, and increase force.
Machine efficiency is a dimensionless quantity that estimates the effectiveness of a device in converting the input power to output power. A machine is a power-driven linkage in which force is done at one point, and the force performs work transferring a load at a different point. Simultaneously, the input power of a machine is equivalent to the product of input force and the velocity of that point; similarly, the output power is equivalent to the product of the force applied on the load and the velocity of the load. The mechanical efficiency is a dimensionless quantity between $0$ and $1$ that is the fraction of the machine's power output to the input power.
$\text{Efficiency} = \dfrac{\text{output power}}{\text{input power}}$
Efficiency is the capacity to avoid dissipating energy, works, property, and time producing a wanted result. It is the strength to do something well, firmly, and without loss. "Efficiency is therefore not an aim in itself. It is not that we want for its benefit, but preferably because it aids us to attain more of the things we appreciate". It means the level of production that utilizes the least amount of information to achieve the actual output. It often comprises the capability of a particular application of force to produce a remarkable outcome with the smallest amount or quantity of waste, cost, or needless effort.

Additional Information:
Since a machine does not carry a source of energy, nor can it collect energy, from conservation of energy, the output power of a machine can never be higher than its input, so the efficiency can never be more than $1$. All real machines lose some energy to friction; the energy is lost or dissipated as heat. Therefore, their output power is less than their power input.

Note:
The efficiency of all existing machines is smaller than $1$. A theoretical machine without resistance or friction is known as an ideal machine, such a machine would not have any power losses, so its power output would equal its input power, and its efficiency will be $1 (100 \%)$.