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Q-reeus
Q-reeus is offline
#7
Jan12-11, 02:47 PM
P: 1,115
Quote Quote by Mueiz View Post
Suppose you have a source that send a very strong straight beam of light (say laser )
Then you direct the light toward a distant wall with angle 45 degree
as show in the drawing below
Then if you rotate the source 90 degree in one second, what is the velocity of the visual effect (spot)on the wall?
According to the distances given in the drawing it must be greater than the spead of light !!!
I do not know if any one think of this before but I hope I will receive more comments and analysis about this simple case.
Attachment 31272
I like to let links do the talking where possible: http://www.weburbia.com/physics/FTL.html see 3. Shadows and Light Spots. One point not mentioned there is that the 'spot' won't be a spot for very fast motion of pointer - becoming an increasingly elongated ellipse along the apparent direction of motion. Ellipticity here being ~ (2*1011)/(3*108) = 666 - basically a faint streak!