Efficiency of Machines
About 2 min read
The efficiency of a machine indicates how well its input energy is converted to useful output energy or work. It is a major factor in the usefulness of a machine and is the fraction or percentage of the output divided by the input.
According to the Law of Conservation of Energy, the total output energy or work must equal the total input energy. However, some of the input energy does not contribute to the output work and is lost to such things as friction and heat.
Examples of machine efficiency include a lever, automobile, and perpetual motion machine.
Questions you may have include:
- What is the efficiency equation?
- How do losses fit in?
- What are some examples of efficiency?
This lesson will answer those questions. Useful tool: Units Conversion
Efficiency equation
The efficiency of a machine concerns how much energy is lost to friction and heat during its operation. Since work is the change in kinetic energy, the efficiency of a machine can be stated as the percentage of the output work divided by the input work minus the work lost from to friction and heat.
Eff = WO/WI
where
- Eff is the efficiency decimal fraction
- WO is the output work or energy
- WI is the input or effort work or energy
Multiply Eff by 100% to get the efficiency percentage.
Losses
According to the Law of Conservation of Energy, the output work or energy equals the input work minus the work lost from to friction and heat:
WO = WI − WLoss
Substituting for WO in the efficiency equation:
Eff = (WI − WLoss)/WI
or
Eff = 1 − WLoss/WI
Examples
Examples of efficiency include a lever and automobile.
Lever
A simple lever loses about 2% or 0.02 of the input energy to internal friction at its fulcrum:
WLoss = 0.02WI
Thus:
Eff = 1 − 0.02WI/WI
Eff = 1 − 0.02
Eff = 0.98 or 98%
Automobile
On the other hand, the efficiency of an automobile is only around 15%. About 75% of the energy is lost through wasted heat from the engine and another 10% is lost due to internal friction, including losses from tire friction.
Perpetual motion machine
If losses to friction and heat are zero, the efficiency of the machine is:
Eff = WO/WO
Eff = 1.0 or 100%
Such a machine is called a perpetual motion machine since once it was started, it would run forever. Inventors have worked for years to create such a machine, but they have been unsuccessful.
Summary
The usefulness of a machine is determined by its efficiency. A machine converts the force provided from an input energy into output work. The Law of Conservation of Energy requires that the total input energy must equal the total output energy.
According to the Law of Conservation of Energy, the total output energy or work must equal the total input energy. However, some of the input energy does not contribute to the output work and is lost to such things as friction and heat.
Examples of machine efficiency include a lever, automobile, and perpetual motion machine.
Use science to make things more efficient
Resources and references
Websites
The Efficiency of Machines (PDF) – Carolina Curriculum
Mechanical Efficiency – Wikipedia