# 0.30 Phy1300: angular momentum -- rotational kinetic energy and  (Page 11/11)

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## A flywheel

A flywheel is a device that is commonly used to smooth out the irregularities of angular velocity in rotational motion. For example, in the age of steam engines, therotational motion was powered only during a portion of each cycle, and was coasting during the remainder of the cycle. Unless corrected, therefore, aloaded steam engine output shaft would speed up and slow down once during each rotation of the shaft.

The correction

Most steam engines employed a large flywheel that was turned by the output shaft to cause the angular velocity toremain relatively constant despite the fact that rotational power was applied during only a portion of the cycle.

When rotational power was applied to the output shaft, the shaft turned the flywheel. When rotational power was not applied to the output shaft, theflywheel turned the shaft. Because the flywheel had a large rotational inertia, it preferred to turn at a near constant angular velocity.

Physically, the flywheels were usually large wheels with spokes and most of the mass distributed in a rim at thecircumference of the wheel. This configuration produced a large rotational inertia for a given amount of mass and a given amount of available space.

## What have we learned?

Perhaps the most important thing for you to take away from this module is that

• although the rotational inertia of a rotating object is influenced by the mass of the object,
• it is also very heavily influenced by the geometrical distribution of that mass.

Two rotating objects having exactly the same mass can have entirely different rotational inertia values (moments of inertia).

For example, a flywheel with the bulk of its mass concentrated a large distance from the axis of rotation is much more effective in smoothing out theangular velocity of the device than would be a flywheel with the same mass concentrated in a small radius near the axis of rotation.

## Work through the examples

I encourage you to work through the examples that I have presented in this lesson to confirm that you get the same results. Experiment withthe examples, making changes, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.

## Resources

I will publish a module containing consolidated links to resources on my Connexions web page and will update and add to the list as additional modulesin this collection are published.

## Miscellaneous

This section contains a variety of miscellaneous information.

Housekeeping material
• Module name: Angular Momentum -- Rotational Kinetic Energy and Inertia
• File: Phy1300.htm
• Revised: 10/02/15
• Keywords:
• physics
• accessible
• accessibility
• blind
• graph board
• protractor
• refreshable Braille display
• JavaScript
• trigonometry
• rotational kinetic energy
• rotational inertia
• moment of inertia
• Atwood machine
• flywheel
Disclaimers:

Financial : Although the openstax CNX site makes it possible for you to download a PDF file for the collection that contains thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.

You also need to know that Prof. Baldwin receives no financial compensation from openstax CNX even if you purchase the PDF version of the collection.

In the past, unknown individuals have copied Prof. Baldwin's modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing Prof. Baldwin as the author.Prof. Baldwin neither receives compensation for those sales nor does he know who doesreceive compensation. If you purchase such a book, please be aware that it is a copy of a collection that is freelyavailable on openstax CNX and that it was made and published without the prior knowledge of Prof. Baldwin.

Affiliation : Prof. Baldwin is a professor of Computer Information Technology at Austin Community College in Austin, TX.

-end-

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