Re: [Phys-l] picket fence free fall vs. ticker tape timer

[Brian Whatcott <betwys1@sbcglobal.net>]

At 02:28 PM 9/15/2007, you wrote:
> I remember reading an article last year on the error in using position-time
> data (like a ticker-tape) in calculating the acceleration of a freely falling
> object.  In particular, I think it referred to using position time 
> data from a
> "picket fence" apparatus with regularly spaced opaque and transparent strips
> falling through a photogate.  I have searched my paper files and the internet
> to no avail.  Does this sound familiar to anyone who could point me in the
> proper direction?
>
> Thanks
>
> Justin Parke


It's possible that Justin has in mind the error source familiar to users of
iterative methods of dynamics calculations. Briefly: if you start from
 position/time data and effectively differentiate  (more properly,
 difference) the data twice to get acceleration, the variability
 inherent to individual position values is exaggerated.
People using this approach are adjured to start at the highest difference
and integrate (more properly sum) as required. This smoothes errors.



Brian Whatcott    Altus OK    Eureka!