Re: free fall data

[brian whatcott <inet@intellisys.net>]

At 13:41 9/13/97 EDT, you wrote:
> Suppose a common VHS camcorder is used to collect free fall data. Would
> it be better (from the point of view of unavoidable line resolution and 
> pixel errors) to turn the camcorder sidewise? Are the more expensive
> camcorders better than ordinary VHS? How much better? Assume that frames 
> are digitized at the best available resolution of 680 by 480 pixels.
>
>                                                       Ludwik Kowalski

The definition in the vertical and horizontal axis of the TV picture
are meant to be comparable. There is a seperate issue concerning
transmitted pictures which can show momentary or persistant horizontal
displacements 
( to the right). This ghosting is due to multi path reception.

   It seems that if one maximizes the target's displacement in the viewable
frame, i.e. by using as big a zoom as possible, and above all, by taking at
least 20 repetitions of the action, one can expect to produce the most
accurate results.

 Recall that the image is conveyed to the TV as an interlaced picture in
two halves by which means the second half of the frame fills in every other
scan line.

 There is an experimental design consideration.
 We have mentioned tossing a brick from a vehicle.
You are undoubtedly aware of the difficulty of visually assigning the
position of the center of mass in such an image. A pool ball, or using
Leigh's experimental object, a bowling ball might be more satisfactory in
that particular case.

Regards

brian whatcott <inet@intellisys.net>
Altus OK