How to calculate torque of a rotating wheel at constant angular speed?


by sixelements
Tags: angular, constant, rotating, speed, torque, wheel
sixelements
sixelements is offline
#1
Jul21-11, 10:13 AM
P: 1
Suppose there is a rotating wheel at constant angular speed, i.e, 1000 RPM (Revolution Per Minute). What is the torque of Earth at certain location? The equator should have the maximum torque value.

I find the angular speed w by 1000 x 2Pi rad x 1 / 60s = 104.71 rad/s
Assume M is the mass of the rotating wheel. R is the radius.

Because it's revolving at a constant angular speed, the tangential angular acceleration (alpha t ) is zero.

I can get the inertia (I) and kinetic energy K by formulas. Then, I'm kind of stuck how to find out the torque?
Read through the rotation chapter of physics book have twice, checked all the examples without success.

What am I missing here?

Thanks in advance.
Phys.Org News Partner Science news on Phys.org
Going nuts? Turkey looks to pistachios to heat new eco-city
Space-tested fluid flow concept advances infectious disease diagnoses
SpaceX launches supplies to space station (Update)
SteamKing
SteamKing is offline
#2
Jul21-11, 10:44 AM
HW Helper
Thanks
P: 5,543
The presence of a torque will cause a change in the angular velocity of a wheel. (In this case, torque and its effect on angular velocity is analogous to the effect a force has in changing the velocity of a mass in rectilinear motion.) If a body is rotating with a constant angular velocity, the net torque is zero.

As to What is the torque of the Earth, you will have to explain what you are looking for in more detail.
gsal
gsal is offline
#3
Jul21-11, 01:36 PM
P: 838
I think the only torque involved is the one to overcome friction and that's it...at this point, the mass of the wheel is irrelevant.

If you think the gravity of earth is helping turn the wheel, I presume the shaft of the wheel is horizontal correct? In any case, gravity does not help at all...after all, for every piece of mass coming down in one half of the wheel, there is another one going up on the other side and so, the effect of gravity is a wash.

...if non of this answers your question...then I don't know what in the earth you are talking about :-)

BobG
BobG is offline
#4
Jul22-11, 03:15 PM
Sci Advisor
HW Helper
BobG's Avatar
P: 2,275

How to calculate torque of a rotating wheel at constant angular speed?


Quote Quote by sixelements View Post
Suppose there is a rotating wheel at constant angular speed, i.e, 1000 RPM (Revolution Per Minute). What is the torque of Earth at certain location? The equator should have the maximum torque value.

I find the angular speed w by 1000 x 2Pi rad x 1 / 60s = 104.71 rad/s
Assume M is the mass of the rotating wheel. R is the radius.

Because it's revolving at a constant angular speed, the tangential angular acceleration (alpha t ) is zero.

I can get the inertia (I) and kinetic energy K by formulas. Then, I'm kind of stuck how to find out the torque?
I'm at a loss as to what you're trying to ask. The Earth's gravity will have no effect on how fast the wheel is spinning. If the wheel's axis is aligned with the Earth's radius and the wheel is rotating at a constant speed, the angular acceleration and the torque is zero.

Or, since you ask about the torque of the Earth, are you asking about precession?

http://hyperphysics.phy-astr.gsu.edu/hbase/rotv2.html


Register to reply

Related Discussions
Calculate resultant forces with external torque on rotating system at constant speed Classical Physics 0
Solve for torque on wheel with offset center of mass and constant angular velocity Advanced Physics Homework 0
Constant angular acceleration of a rotating wheel Introductory Physics Homework 1
Does Torque act on a disc rotating with constant angular velocity Classical Physics 4
calculate wheel torque based on known Weight, wheel size, acceleration data ? General Physics 9