Flywheel

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, (reciprocating) 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. They are particularly 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.

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The kinetic energy stored in a rotating flywheel is

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:E = rac{1}{2} I omega^2

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where I is the moment of inertia of the mass about the center of rotation and omega (omega) 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. 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.

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The flywheel has been used since ancient times, the most common traditional example being the potter's wheel. In the Industrial Revolution, James Watt contributed to the development of the flywheel in the steam engine.

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Repository: A repository is a central place where data is stored and maintained. A repository can be a place where multiple databases or files are located for distribution over a network, or a repository can be a location that is directly accessible to the user without having to travel across a network....

Angular momentum: In physics the angular momentum of an object with respect to a reference point is a measure for the extent to which, and the direction in which, the object rotates about the reference point....

Rotation: :This article is about rotation as a movement of a physical body. For other meanings, see rotation (disambiguation)....