Re: [Phys-l] standing wave experiment

["Rauber, Joel" <Joel.Rauber@SDSTATE.EDU>]

> Since (I believe) the problem here is that PASCO supplies (even sells)
> this
> string with their wave motion vibrators, one might think this is good
> stuff
> with which to work.  I bit and ordered a reel of the string when we
> bought
> the vibrators.  That reel remains sealed!  The big stretchy stuff is
> fine
> for showing standing waves (demo mode), but I prefer a 20ft long coiled
> spring for that.  I actually have not seen the reported behavior, but
> the
> stretching of the string makes the traditional experiment impossible
> since
> knowing the mass/length of the string becomes a function of the tension
> on
> the string.  Too complicated.  We have some 50 lb test fishing line

Actually, if you want your lab to be a little more involved in the art of experimentation; its not that hard to take it into account.  We take a sample string and put under the same tension as what you have on the vibrating apparatus, measure its mass and measure its length to get the mass per unit length under the actual tension used.  It fairly easy to do and gets across the idea of doing procedures that correct for possible systematic sources of error.