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We're just saying that the distribution of that mass away from the centerline will affect how quickly the rotating assembly can be accelerated.
Yeah, I know. And That's incorrect. If the moment of inertia is the same than rotational acceleration is the same. This is just high school physics.
If you want to keep the mass closer to the centerline you'll need to add more of it to keep balance.
you would really need to understand how engines are balanced to understand why it's not as simple as you think.
here's a little more info compliments of the internet.
Moment of inertia is the term used to measure or quantify the amount of mass located at an object's extremities. For example if all the mass of an object was located in a small compact size (like a lead ball) its moment of inertia would be small compared to the same amount of mass shaped into a dumbell. Because a dumbell has most of its mass located farther from its center. But there is a "qualification" here. Moment of inertia is calculated relative to a hypothetical spin axis. Once you choose the spin axis then you calculate the moment of inertia by multiplying the mass times its distance to the spin axis squared; I = MR^2
So in the example between the sphere and the dumbell the moment of inertia of the dumbell would be significantly larger relative to a spin axis perpendicular to the dumbell length. If you instead choose your spin axis to lie thru the dumbell parallel to its length then its moment of inertia,relative to this axis, would be much smaller because the mass would be located closer to that axis. And ,in fact, it might even be smaller then the moment of inertia of a sphere about an axis thru its center.
A way to store kinetic energy is with a spinning object. In calculating how much energy would be stored in a spinning object the energy is proportional to the moment of inertia. So all other things being equal you would choose a spin axis and object shape that gave you the largest moment of inertia for maximum stored energy.
Last edited by Performance Only; 01/19/12 02:04 AM.
