Re: Forces in rods, ropes, etc.

[brian whatcott <inet@intellisys.net>]

At 21:59 9/4/97 EDT, you wrote:
> ...
> 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
It is a very easily arranged demonstration to suddenly apply a voltage
from a battery to a coax transmission line. If there is a series resistor
about equal to the characteristic impedence of the coax, typically 50 or 75
ohms, in series with the battery, an oscilloscope will first show a step
from zero volts to HALF the battery voltage.
 Then when the steep wave front has progressed to the (open ) far end of
the coax, it travels back at the level of the full battery voltage, finally
reaching the battery end.
 Its steady state is as an open circuit.

However, Bill's transmission line was well-terminated, so the battery
tension will result in a continuing current even after the steep leading
edge has progressed to the end.

I hope this answers your question.
Regards

brian whatcott <inet@intellisys.net>
Altus OK