Question
Hello, I have a doubt about inertia in a uniform bar and axis of rotation..
What's the difference between a lengthwise axis and a parallel one?
In some books I have found that when we're talking about lengthwise axis that pass through the center of the bar the inertia of the bar is equal to the inertia of a cylinder, and when it's about parallel axis that pass through the bar , the inertia is zero. I'm really confused with that words...
I'm not talking about the parallel axis theorem...
Thanks for any answer
What's the difference between a lengthwise axis and a parallel one?
In some books I have found that when we're talking about lengthwise axis that pass through the center of the bar the inertia of the bar is equal to the inertia of a cylinder, and when it's about parallel axis that pass through the bar , the inertia is zero. I'm really confused with that words...
I'm not talking about the parallel axis theorem...
Thanks for any answer
Answers
bobpursley
https://www.physicsforums.com/threads/moment-of-inertia-of-a-rod-at-an-angle.449943/
Damon
If it passes through the bar along the axis of the bar, the moment of inertia is small because the mass is close to the axis of rotation. Remember that mR^2 stuff.
It is not zero though unless the radius of the bar is zero :) It is in fact a slender solid cylinder and its moment of inertia is
(1/2) mR^2
in the other direction, like spinning a baton about the center, it is much bigger
(1/12) m L^2
Note - L^2 is presumably HUGE compared to R^2
It is not zero though unless the radius of the bar is zero :) It is in fact a slender solid cylinder and its moment of inertia is
(1/2) mR^2
in the other direction, like spinning a baton about the center, it is much bigger
(1/12) m L^2
Note - L^2 is presumably HUGE compared to R^2