A
flywheel is a heavy rotating disk used as a repository for
angular momentum. Flywheels resist changes in their rotation speed, which helps steady the rotation of the shaft when an uneven
torque is exerted on it by its power source (such as a
piston-based
engine) or when the load placed on it is intermittent (such as a piston-based
pump). Flywheels can also be used by small motors to store up energy over a long period of time and then release it over a shorter period of time, temporarily magnifying its power output for that brief period. Recently, flywheels have become the subject of extensive research as power storage devices; see
flywheel energy storage.
The kinetic energy stored in a rotating flywheel is
- <math>\frac{1}{2}I\omega^2</math>
where I is the moment of inertia of the mass about the center of rotation and ω is the angular velocity in radian units. A flywheel is more effective when its inertia is larger, as when its mass is located farther from the center of rotation either due to a more massive rim or due to a larger diameter.
The flywheel was developed by James Watt in his work on the steam engine.
See also gyroscope, momentum wheel
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