

Rotational Dynamics
Name: Justin D.
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: 20002001
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 coworker 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(meterssquared)/(seconds).
Another possible unit is kg.m^2.rpm =
(kilograms)x(meterssquared)x(revolutions per minute). Angular momentum,
like linear momentum, requires a massfactor.
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 rpmvalue, 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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Update: June 2012

