String stretching debate: Experiment Idea

[John Delacour]

At 01:50 -0500 18/4/08, kurt baxter wrote:

>...I have two ideas for experiments:
>
>1) Suspend a 150 weight with piano wire.
>     Make two marks near the ends of the wire (to avoid any 
>complications from "settling" of  termination point knots or grips)
>     Measure distance between marks immediately after hanging.
>     Days or weeks later, measure again.
>
>If there is any sort of slow, creeping stretch occurring, in a weeks 
>time the two marks should have traveled away from each other 
>slightly.

There are better ways to do it and to get useful data from the 
experiment.  Even if a long length of wire is used -- I plan to use 
about 8 feet -- there will be a great error in reading the small 
movement of the marks and no useful quantities will be obtained.  I 
will explain later how the experiment can be made more useful.

It is also important to do many tests to measure the extension under 
different conditions, particularly with weights that bring the wire 
to different percentages of its breaking strain, since loading the 
wire with too little tension may well lead to very different results, 
as Vicat discovered.

JD