Re: Forces in rodes, ropes, etc.

[LUDWIK KOWALSKI <kowalskil@alpha.montclair.edu>]

> > Is it also bad physics to say that "forces are transmitted" (when
> > applied through rods, ropes and pistons)? ...

> Mechanical forces transmitted through rods ...  "travel" as waves
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A constant horizontal force F is applied (through a rod) on a brick 
sliding over a frictionless horizontal surface. The mass of the rod is 
negligibly small in comparison with the mass of the brick, M. We all 
know that the rod must be compressed (pairs of equal and opposite 
forces |F1|=|F2|=F are established along its length) and that a=F/M.

Is the tension in the rod real? Or "it lacks the reality possesed by 
charge", mass, temperature, pigmentation density and other attributes
of a material object?

The wave (a single pulse disturbance, no reflection, as specified by Bill) 
exists only between moment t1, when F is applied at "the input of the rod",
and t2=t1+L/s, when F first is applied to the brick. L is the length of the 
rod and s is the speed of sound in it. Is it BAD PHYSICS to say that a 
force is also transmitted when t>t2, as long as F remains constant? 
I am sorry this detail was not specified in my original question. 
                                                         Ludwik Kowalski