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Name:  Justin D.
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: 2000-2001


Question:
PLEASE, PLEASE help me! My name is Justin. I am having a very hard time finding a math formula. I am looking for a formula to calculate the resistance a flyweel, or gyroscope creates when you try to change its angular momentum. Is the resistance equal to the rate change of the the angular momentum and the rpm of the wheel (with centripical force of the spining wheel calculated respectfully)>EXAMPLE: 360 degrees of change in angular momentum or 1 complete rota> > >of change to 10 rotations of a wheel exerting 1 lb of centrifical for> > >what would be the resistance of the rate of change in angular momentum. (im sorry if my question is hard to understand, i don't know if i completly understand it myself.) Could someone please explain as best thay can how to calculate the resistance to change in momentum. A formula would be best, and if someone is keen on the subject please include the precesion of the wheel when moved and how to calculat the rate of precesion to rate of change (I AM SO SORRY FOR THE GRAMER, SPELLING, AND LAYMAN EXPLANATION OF MY PROBLEM)


Replies:
I have tried to obtain a formula over the internet to suit my needs but have thus far been unsucessfull due to lack of previous knowledge and experiance in physics. I have a (fair) understanding in how related formulas work but don't understand most of the symbles, or what thay represent. I know that you could probubly care less, and your answer was more than sufficiant to the content of my previous question.

Please take a minute to read my email to you for an opertunity to help an ambitious inventer. If you can help me in this area of Rotational Dynamics, I am willing to compensate you with a reasonabaly appropriat amount of funds, to which we may discuss.

First of all, let me tell you a little about myself. My name is not realy Justin, it is Jesse, and to keep myself unexposed over the internet i wish to keep my last name to myself. You may just call me Jesse. My personal interest in physics, enginering, and inventing started when i was 18 years old. I woked for a company called Peterson inc for 4 years durring which time myself and a fellow co-worker did extensive resurch and development on the THIOKAL ATLAS4a rocket booster for Lockheed Martin Astronautics. The production of the rockets were transfered to Peterson for us to reinvent the equipment necessary to rebuild 20 year old tecnology. I have had the opertunity to work side by side with some of the worlds best metalurgests and enginers from lockheed (Bill fitzgerald), Thiokal (George stailey), to name a few. By nature I am a Journeyman welder, thus reflected in my grammer. My experiance in enginering is uncertified, by was ubtained through this field.

To get to the point and not to bore or wast your time, If you are somewhat experianced in this field of rotational dynamics, I would like to aquire your help. I hope you can understand that I can not revial the nature of my work. Please reply to this email even if you are not interested. If you are et me know and I will list, in more detail, the senerio for the information that I am desprate to aquire


Justin,

The first thing to get right is terminology, and units. rpm is a unit for angular velocity, NOT angular momentum. A standard unit for angular momentum is kg.m^2/s: (kilograms)x(meters-squared)/(seconds). Another possible unit is kg.m^2.rpm = (kilograms)x(meters-squared)x(revolutions per minute). Angular momentum, like linear momentum, requires a mass-factor.

There is no real resistance to a change of angular momentum, just as there is no actual resistance to a change of linear momentum. If an object feels a net force for a length of time, the linear momentum changes by the product of the net force and the time. If an object is twisted with a net torque for a certain time, angular momentum changes by the product of the torque and the time.

If you are looking for resistance to changing the rpm-value, then you are looking for resistance to changing the angular velocity: how fast the object is spinning. You are looking for resistance to angular acceleration. The formula relating to this is:

Torque = (Moment of Inertia)x(Angular Acceleration)

The torque is how hard the object is being twisted, how hard you are trying to change its rotational motion. Angular acceleration is how fast the angular velocity is changing. Moment of inertia is the object's resistance to rotational change. With linear motion, the resistance to change oof velocity is mass: F=ma. With rotational motion, it is moment of inertia. I recommend you look up "moment of inertia" in a physics text, or perhaps an encyclopedia. It takes more space to explain than is reasonable for this letter.

Dr. Ken Mellendorf
Illinois Central College



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