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Re: Forces in rodes, ropes, etc.



Ludwik asks if it is "bad physics" to say that a rod under constant
compression transmits a force. It certainly works as a figure of
speech; we all know what it means. I won't attach a pejorative to it,
but let me ask this question:

If the compression is time invariant, in which direction is the force
"transmitted"?

My idea of transmission entails a direction, and this physical system
seems to have an ambiguity there. I wouldn't like to suggest that the
term "transmission" is appropriate except in cases where the stress
varies in time, as in Pascal's principle: a *change* in the pressure
in one part of a confined fluid is communicated equally to all parts
of the fluid. This "communication" too is limited by the speed of
sound in the fluid. I don't know if Pascal appreciated that point.

Thinking's fun, in any event.

Leigh