Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

[Phys-L] Rotation of a Rolling Ball.

I was considering a Galilean problem on Quora of a ball moving at a given velocity climbing a ramp of given height without slipping.
The question asked about its final velocity after the ascent.
This depends upon its  kinetic energy, and how much is converted to potential energy.
I considered two possibilities: solid sphere and hollow sphere.
I used two moments of inertia for these cases:2/5*m*r^2 & 3/5*m*r^2

These happen to be the values used by Dan MacIsaac in his 1996 video tutorial at Buffalo, and by John Yelton at Oxford U., when upvoting a similar calculation recently.

Then I happened on a list of Moments:
1) a sphere spinning on a central axis 2/5*m*r^2
2) a sphere rolling on a surface       7/5*m*r*2
And I was taken aback.
The academic sources seem to be juggling the measure for rotation to make the lower value of Moment work, ignoring the axis of rotation offset correction.
What am I missing?

Brian W