### Flywheel Effect or Polar Moment of Inertia

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The flywheel effect, sometimes also referred to as "Mass Momentum", is a term used to describe the property of a system to remain at a given velocity or kinetic energy. It is generally applied to rotating mass, such as flywheels or clutch plates.

The following equations and calculator will estimate the Flywheel Effect or Polar Moment of Inertia.

Description Equation
Flywheel Effect or Polar Moment of Inertia
Mean Angular Velocity
Coefficient of Steadiness

Where:

Symbol Description Units
Wk2 Flywheel Effect or Polar
Moment of Inertia
kN (lbf)
W Weight of Flywheel N (lbs)
E Excess energy J (ft-lbf)
g Acceleration due to gravity 9.8 m/s2
(32.16 ft/s2)
n1 Maximum speed rpm
n2 Minimum speed rpm
Average speed rad/s
Maximum and minimum
angular speed, respectively
rad/s
m Coefficient of Steadiness -
Cf Coefficient of Fluctuation
of Rotation
See Table

Coefficient of Fluctuation of Rotation Table, Cf
Driven machine Type of drive Cf
AC generators, single or parallel Direct-coupled 0.01
AC generators, single or parallel Belt 0.0167
DC generators, single or parallel Direct-coupled 0.0143
DC generators, single or parallel Belt 0.029
Spinning machinery Belt 0.02–0.015
Compressor, pumps Gears 0.02
Paper, textiles, and flour mills Belt 0.025–0.02
Woodworking and metalworking machinery Belt 0.0333
Shears and pumps Flexible coupling 0.05–0.04
Concrete mixers, excavators, and compressors Belt 0.143–0.1
Crushers, hammers, and punch presses Belt 0.2