Re: MATH PHYSICS

["Polvani, Donald G." <donald_g_polvani@MD.NORTHGRUM.COM>]

Brian W wrote:

> > Not much air resistance in an oil bath, I would have thought, Jack.

> > Could it be that it makes the sums work a little better?

In fact the drag force on a "slowly moving" sphere is proportional to
velocity and not the square of velocity.  This applies for motions in which
the Reynolds number (i.e. 2xradiusxvelocity/kinematic viscosity)is small.
For a sphere of one mm radius, moving in water, the velocity must be less
than 0.2 cm/s.  See, for example, L.M. Milne-Thomson, "Theoretical
Hydrodynamics", fifth edition, 1968, pp 681,682.

Don Polvani
-----Original Message-----
From: Brian Whatcott [mailto:inet@INTELLISYS.NET]
Sent: Tuesday, November 27, 2001 1:46 PM
To: PHYS-L@lists.nau.edu
Subject: Re: MATH PHYSICS



Brian W

At 09:15 AM 11/27/01, you wrote:
>         You're missing low velocity viscous drag, as used in analyzing the
> Millikan oil-drop experiment.  See chapter 12 of "The Mechanical Universe"
> (standard edition).
>                         Regards,
>                                 Jack
>
> On Mon, 26 Nov 2001, Brian Whatcott wrote:
>
> > > David Abineri wrote:
> > > > If one assumes that a projectile encounters an air resistance
> > > > proportional to velocity, one can write a differential equation like
> > > > mr''=-mgj - kr' which can be solved for r using an integrating
factor
> > > > e^(kt/m).
> > > >
> > > > The final solution for r, however, does not admit an interpretation
for
> > > > k=0.  Why is it that one does not get the ideal case to come from
this
> > > > more general case when k=0?
> > > >
> > > > I hope that the question makes sense.
> >
> >
> > Not to me. The assumption is unphysical, in my view.
> > Cd is proportional to  V^2 ??
> >   What am I missing, would you say?
> >
> >
> > Brian Whatcott
> >    Altus OK                      Eureka!

Brian Whatcott
   Altus OK                      Eureka!