Re: videotape data on free fall

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

On Fri, 24 Oct 1997 BOB SCIAMANDA wrote:

> > Each TV line takes roughly 50 microseconds,  each field about 8 ms and 
> > each frame about 16 ms.  Furthermore the two fields which make up a frame 
> > may be interlaced.  Given this, how does one interpret data taken with a 
> > shutter speed of 1/1000 sec (1 ms)?

On Fri, 24 Oct 1997 Leigh Palmer <palmer@sfu.ca> wrote:

> If one can judge by the product, the image is frozen on the CCD in a
> millisecond. That's whey they call it a "shutter speed". Of course
> it is transmitted in a thirtieth of a second (approximately), and it
> is *always* interlaced in NTSC TV. Examination of the single frame,
> however, will show the spokes of wheels as straight lines at 1/1000
> shutter speed. That would not be the case if the particular millisecond 
> corresponding to the pixel being transmitted was the one of interest. 
> In that case the spokes would be curved and some might even be missing.

I also observed the "rotating spoke", the hand of a fast timer which makes
one rotation in each second. The hand was not curved (two ordinary old 
camcorders). And it was always exactly 30 pictures for each rotation.

                                  Ludwik Kowalski
........................................................................
               
Leigh added:
> Since time resolution seems to be a problem, have you considered taking 
> the experiment outside? Drop a lead fishing weight from a third story 
> window and videotape it.

How can this help? I would have to be far away; the number of pixels (and
lines) is fixed. I do not think that errots are in dt=1/30 second. My data
were already presented (two months ago) and I have not been able to do 
anything better. Can somebody else share the free fall data? By how much
do individual accelerations fluctuate in consecutive time intervals?