David and Tim ... Very good and along the "expected" (by me!) track esp. in
relation to end points and total distance traveled. 3 inches. Interesting ...
interesting ... you all want to concentrate on the fact that there is no such
thing as totally black so the background must have added some exposure and thus
lightened the middle areas in particular which might have reached 1.3 in density
if the background had been a black hole? And thus the moving object might have
produced a density associated with 1/30 second. And then speed would be ...
Something more to ponder maybe? I wonder how the class is going to respond.
In any case this was meant to activate "gray cells" - hopefully it did that!
andy
I hope this is not too easy a question ... what do you think.
Tim Corio wrote:
The lower image is a blurred image of a square object. It is blurred
because the object was in motion.
The white object moves three inches. This is determined by comparing
the length of the second image with the side-by-side images above it.
The squares have a space between them so as a ruler they are actually
slightly more than one inch each, but I've chosen to ignore that for
this exercise.
The object is moving at a constant rate. This is determined by
observing the even brightness of the image.
The dark ends are the result of the amount of time the subject is "in
front of" that piece of film. In the center of the image the subject is
in front of a given point for the amount of time it takes an object to
move one inch when traveling at 170.45 MPH. Since the object moves
three inches in this exposure and the object one inch wide it is in
front of a point in the center for 1/3000 second.
We can not tell if the object was moving left-to-right or right-to left.
At the beginning of the exposure the object was at one of the edges. At
the leading edge, the object had left that point in almost zero time
during the exposure, That is why the exposure is dark there. At the
trailing edge the object is just arriving at the end of the exposure.
Again there is almost zero time for exposure there. In the center of
the image there is a two inch segment where the exposure is constant.
any given point in that segment was illuminated by the object for 1/3000
second. To the right an left of that segment any given point is
illuminated for a lesser time.
The moving object has a reflection density of 1.25. This is between the
values for the exposures of 1/15 and 1/30 of a second. That means the
moving subject was "over" a point in the center of the image for between
1/15 and 1/30 of a second. Therefore it was moving between 15 and 30
inches per second. The exposure was between 1/5 and 1/10 of a second.
Either that, or the object is moving at nearly the speed of light. It
is glowing white hot at a brightness not normally observed on earth.
And time dilation has spread it out over a short distance. The shutter
speed must be nearly instantaneous for all practical purposes.
Either way is fine with me.
Tim
