Speeding Radar Guns -
:-o :-o :-o
Do you need a mirror on your car go get ticketted for speeding ?
doesn't need to be metal, just to bounce the radar back.
You can measure the speed of tennis balls and cricket balls, and they aren't traditionally known as reflectors (except for the fact that we can see them)
Note that I used the word "mirror," as in something that "reflects back" the electro-magnetic radiation that was directed towards it. Any object would reflect it back to different degrees, depending on the composition & angle of the object's surfaces, such as "stealth" aircraft is designed in such a way as to both "absorb & reflect" incoming radar signals, however the reflected signals bounce off at angles different than the incoming "angle of incidence" - the angle of the directed "signal."
So, no one said that this "mirror" has to be a "metal." I didn't even used the word "metal." A rock, a jelly fish, a tennis ball, etc. can reflect back microwave radar signals directed towards them. Even your body reflects back incoming microwave (electro-magnetic) radar signals...
There are also some new technologies, not discussed here, that use a “laser light,” instead of a “microwave signal,” in order to catch the “unlawful speeders” & so that their “microwave” only “radar detectors” can not notify them of a near by “smokey.” However, there are already available newer “radar detectors,” & have existed for quite some time, that will also detect these “laser” based “speed guns.”
Now, if you want to measure the speed at which "visible light" travels, then you do need a "mirror" that will reflect "visible light," of course. But that, has nothing to do w/ a "microwave speed radar gun." We are now talking about a completely different "experiment."