Re: free fall data

[LUDWIK KOWALSKI <kowalskil@alpha.montclair.edu>]

OOP, ignore the previously posted  wording. I ment to say position, not speed.

I am responding to this message:

> I avoid noise in the free fall data by having the students use 16
> positions evenly spaced in time.  The key point is that *no* position
> gets used more than once.  I ask them to calculate the average velocity
> between the 1st and 9th point, the 2nd and 10th point, etc. to the 8 and
> 16th points.  This means they only get 8 velocities, BUT THEY ARE
> INDEPENDENT, AND ARE OVER LONG DISTANCES-SO SMALL POSITION ERRORS ARE'T
> FATAL.  

Suppose the time dependence of y is triangular. The position goes from zero
to 10 when t is between 0 and 5 seconds, then it goes from 10 to 0 when t 
is between 5 and 10 seconds. You measure y every second and collect 11 data
points. To avoid using the same position twice you calculate average v 
between points 0 and 6, 1 and 7, etc. And you come to a WRONG conclusion 
that there is no acceleration; the averge v remains constant. 
                                                           Ludwik Kowalski