Re: [Phys-L] overdamping

[Craig Wiegert <wiegert@physast.uga.edu>]

On 10/21/2015 04:20 PM, Carl Mungan wrote:
> I’m probably just not thinking about things clearly, but the
> following seems unintuitive to me.
>
> Imagine a mass m on a spring k in a viscous fluid so that we have
> Stokes’ drag -bv where v is the velocity of the object.
> ...
> * but the one that puzzles me is m - I know the answer is you have to
> decrease m to get overdamping, but my intuition says it should be
> opposite because it should be harder for a bigger mass to oscillate

It seems to me the k/m factor takes into account "how hard it is to
oscillate a large mass"; the b/(2m) factor has nothing to do with
oscillation.  (Well, that's not exactly true, but roughly speaking.)

The b/(2m) factor would be "how hard it is to *slow down* a large mass",
whether or not it's oscillating.  It's easier for molasses to slow a
baseball than a lead ball of the same diameter.

-- 
----------------------------------------------------------------------
Craig Wiegert                           Office: 215 Physics Building
Undergraduate Physics Coordinator
Associate Professor                     Phone: 706-542-4023
Department of Physics & Astronomy       Fax: 706-542-2492
University of Georgia                   Email: wiegert@physast.uga.edu
Athens, GA  30602-2451                         cwiegert@uga.edu