Displacements

[John Cooper <jcooper@BUCKNELL.EDU>]

On Thu, 5 Aug 1999, DEVARAKONDA VENKATA NARAYANA SARMA wrote:

> Have you cosidered force acting on the hand due to the
> wall as a function of time and can we be sure that there is no
> displacement of the hand during this interval.  Interaction always
> involves finite intervals and in such a finite interval there is
> always displacement.
  Decades ago, as a freshman in physics, I asked the instructor how the
floor could possibly 'know' precisely how much force to exert against my
foot so that I neither sank into into the floor or nor was repelled above
it.  Of course, I was mocked and ridiculed for the stupidity of the
question.
  It wasn't until I was in a senior level quantum chemistry course, where
I encountered force constants for vibrations of bonds, that I evolved the
picture of a solid as a three dimensional lattice of interconnected
springs, like an old camp cot but in 3-d.
  I am confident there are displacements .. but of the order of fractions
of nm .. more like lattice deformations.

 John N. Cooper, Chemistry
 Bucknell University
 Lewisburg PA 17837-2005
 jcooper@bucknell.edu
 http://www.facstaff.bucknell.edu/jcooper
 VOX 570-577-3673    FAX 570-577-1739