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.

Six Spoke Flywheel

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	-
C_f	Coefficient of Fluctuation of Rotation	See Table

Coefficient of Fluctuation of Rotation Table, Cf
Driven machine	Type of drive	C_f
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