? for Nathan Say

[Roark]

Nathan,

In another post you commented that hollow spheres on

a dumbell would not be as prone to rotation as solid

spheres. Am I correct in assuming then that Inch's 75 lb

hollow bell would be easier to lift than say a dumbell of

equal weight but, of course, smaller solid spheres?

Thanks.

[Nathan Say]

Yeah, if the diameters are different, but the masses are the same, the one with the smaller diameter would rotate more easily. One thing you could try to convince yourself would be to get 2 weights (the same of course), hold them in your hand & try rotating them or something, then put one on each end of a broomstick (or something that would't change the total mass very much) & try turning it like a propeller. The standard soapbox racer problem in phys & math classes is to say given 3 spheres with the same diameter, one with the mass concentrated on the inside, one that's uniform (no density change) & one that's a shell (mass concentrated on the outside). Start them all rolling down an incline, which one would get to the bottom first? The one that has the mass concentrated in the middle because it rotates more easliy, then the uniform one, then the shell. (the spheres are supposed to be wheels of a soapbox racer)

[supersqueeze]

Good answer!

-Mike M.

[Roark]

Yes, thank you, Nathan.

[Nathan Say]

Once a dumbell with a larger diameter starts rotating though, it would be harder to stop than a narrower one. I think it would still depend on how big the size difference is though.