haruspex's latest activity

Your approach was to take moments about C, but as I have shown that is awkward because you cannot apply the parallel axis theorem...

The parallel axis theorem applies to a rigid body rotating, as a whole, about a given axis. In this problem, the sphere is not doing...

Yes, because in that view all parts of the sphere are rotating about the same axis as a unit. But I think you do have to be careful...

Of course, but it is only of interest in the context of rotation about some axis. It doesn’t have 'a' moment of inertia in that sense...

Your mistake is in applying the parallel axis theorem. That is only valid for a rigid body rotating as a unit about the axis. It would...

Yes, if you take the same sense as positive for both, but no law says you have to. If ##\theta## is the angle clockwise from vertical...

My wording was sloppy; I should have said "for accelerating up the slope". AI's rolling equation is ##\alpha r=(R-r)\ddot\theta##. If it...

No, ##\Delta s## is greater than that because of the curved surface. Consider e.g. R only marginally greater than r.

Did you see post #13?

Ok, here’s what is wrong with the AI solution. First, "the CM acceleration is ##(R-r)\ddot\theta##, not ##a##” is wrong in that it is...

I have confirmed your result independently. Will try to locate the error in the AI solution, but rightnowI am a passenger on a very...

The OP's analysis appears to be independent of the point in the cycle (other than assuming a nonzero magnitude for the frictional force).

No, that is only an approximation for small displacements. But you don’t use it in what you posted, and the question as you have...

That it is at a known distance from every charge, no matter how those charges are distributed around the two shells. This means we can...

No, that clearly would not be true. But the charge on the inner shell will rearrange so that the potential is the same everywhere on...