In article <4adgeq$41f@spool.cs.wisc.edu>, albert@coral.cs.wisc.edu says...
>In article <4aaaq4$4pb@newsstand.cit.cornell.edu>,
>Bob Neuman wrote:
>>If the shutter speed is the same with both the smaller and lighter
>>lens and the longer and heavier lens, it is likely there would be
>>LESS bad effect from shaking with the longer and heavier lens (more
>>mass X more length = slower motion [or something like that.....]).

>The heavier lens will exhibit less tendency to shake and vibration, >yes,but a longer lens is going to be less stable than a shorter one.The
>closer the center of gravity is to the geometric center of the top of
>the tripod, the more stable it will be. Long lenses also will shake
>more. For example, hold a yardstick at one end between your fingers
>and hit your hand, you will see much more shake than if you cut the
>yardstick down to say 6 inches and repeated the experiment.

Hmmmm.... A few problems here. (1)The original post was about hand-holding, I think. (2)Most (physically) long lenses do have a tripod socket at roughly the center of mass of the camera/lens combination.
(3)If you make your experiment closer to reality, balance a yardstick
in the center and strike it, say, at two inches from the pivot with your
finger - you should experience considerable resistence to motion.
Now balance a 6'' ruler in the center (or, hold it lightly by the end
[to simulate a short lens w/o a tripod socket]), and strike it with your finger the same two inches from the pivot - methinks the short, low-mass ruler will easily go spinning out of your fingers (there will be very little resistence to the short low-mass ruler being moved). A real-world
example would be a 500mm f8 Nikkor mirror vs. a 500mm f4 EDIF Nikkor -
if you have tried either hand-holding both of these lenses, or tripod-mounting them, you have seen how much easier it is to stabilize the longer and heavier 500mm f4. (We are not talking here about short
vs. long focal-lengths.) Perhaps you were refering to, say, the short
and light 200mm f4 Nikkor vs. the long and heavy 80-200mm f2.8 AF
Nikkor (neither one of which has a tripod socket) on the camera
mounted on a tripod. Here, again, while the longer and heavier lens
would be less stable on a too-light tripod, the higher mass and greater length would still win out when it comes to freedom from unwanted motion
(assuming that any motion of the camera/lens/tripod combination is allowed to settle out before the exposure).
Hope this helps.