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].

## CharactersticsEdit

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.

## UsesEdit

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 usesEdit

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 wheelEdit

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 formulaEdit

The kinetic energy stored in a rotating flywheel is

http://upload.wikimedia.org/math/1/4/8/148da762c81d0061d84cb36a21fb1e4e.png

where $ I $ is the moment of inertia of the mass about the center of rotation and $ \omega $ (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 = mv^{2}/2, where linear velocity v is comparable to the rotational velocity, and the mass is comparable to the rotational inertia.

## See alsoEdit

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## External links Edit

- Flywheels - index at
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