In
mechanical engineering
Mechanical engineering is the study of physical machines and mechanism (engineering), mechanisms that may involve force and movement. It is an engineering branch that combines engineering physics and engineering mathematics, mathematics principl ...
, mechanical efficiency is a
dimensionless ratio that measures the
efficiency
Efficiency is the often measurable ability to avoid making mistakes or wasting materials, energy, efforts, money, and time while performing a task. In a more general sense, it is the ability to do things well, successfully, and without waste.
...
of a
mechanism or
machine
A machine is a physical system that uses power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromol ...
in transforming the
power input to the device to power output. A machine is a
mechanical linkage in which
force
In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...
is applied at one point, and the force does
work moving a load at another point. At any instant the power input to a machine is equal to the input force multiplied by the
velocity
Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...
of the input point, similarly the power output is equal to the force exerted on the load multiplied by the velocity of the load. The mechanical efficiency of a machine (often represented by the Greek letter
eta ''η'') is a dimensionless number between 0 and 1 that is the ratio between the power output of the machine and the power input
Since a machine does not contain a source of energy, nor can it store energy, from
conservation of energy the power output of a machine can never be greater than its input, so the efficiency can never be greater than 1.
All real machines lose energy to
friction; the energy is
dissipated as heat. Therefore, their power output is less than their power input
Therefore, the efficiency of all real machines is less than 1. A
hypothetical machine without friction is called an ''
ideal machine''; such a machine would not have any energy losses, so its output power would equal its input power, and its efficiency would be 1 (100%).
For
hydropower
Hydropower (from Ancient Greek -, "water"), also known as water power or water energy, is the use of falling or fast-running water to Electricity generation, produce electricity or to power machines. This is achieved by energy transformation, ...
turbines the efficiency is referred to as hydraulic efficiency.
[IEC standard 60041]
See also
*
Mechanical advantage
*
Thermal efficiency
In thermodynamics, the thermal efficiency (\eta_) is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, steam turbine, steam engine, boiler, furnace, refrigerator, ACs etc.
For ...
*
Electrical efficiency
The efficiency of a system in electronics and electrical engineering is defined as useful power output divided by the total electrical power consumed (a vulgar fraction, fractional Expression (mathematics), expression), typically denoted by the G ...
*
Internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...
*
Electric motor
An electric motor is a machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a electromagnetic coil, wire winding to gene ...
*
Velocity ratio
References
{{Reflist
Mechanisms (engineering)
Energy conversion
Mechanical quantities
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