Spoked flywheel

Constructed based on drawings by Leonardo da Vinci [1].

A flywheel is a heavy rotating disk used as a repository [2] for angular momentum [3].


Flywheels resist changes in their rotation [4], which helps steady the rotation of the shaft when an uneven torque [5] is exerted on it by its power source.


Used in a piston-based, (reciprocating) engine, or in a piston based pump when the load placed on it is intermittent. 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.

The flywheel has been used since ancient times, the most common traditional example being the potter's wheel [6].

Other uses[]

In the Industrial Revolution [7], James Watt [8] contributed to the development of the flywheel in the steam engine.

Recently, flywheels have become the subject of extensive research as power storage devices; see flywheel energy storage.

Special fly wheel[]

A momentum wheel is a type of flywheel useful in satellite pointing operations, in which the flywheels are used to point the satellite's instruments in the correct directions without the use of thrusters.

Energy storage formula[]

The kinetic energy stored in a rotating flywheel is

where is the moment of inertia of the mass about the center of rotation and (omega [9]) is the angular velocity [10] in radian [11] 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. Note the similarity of the above formula to the kinetic energy formula E = mv2/2, where linear velocity v is comparable to the rotational velocity, and the mass is comparable to the rotational inertia.

See also[]

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External links[]