Monday, December 31, 2007

Law Round the Bend, Says Fined Physicist

Y'know, I kept thinking that it's only going to be a matter of time before something like this happens, and it has (at least it is the first time I've seen reported in the news media). A physicist is challenging his speeding fine that was based on a "speed camera".

Dr Fielden, 41, said: "Speed cameras are designed only to work on a straight line. As a physicist, I know that radars, which the cameras use, travel in straight lines. If you set one up on a curve, it is going to be inaccurate."

I wish the news report had more details on this "speed camera", i.e. how it determines the speed of a vehicle. If all it does is detects either "incoming" or "outgoing" motion, then there's something not quite right with this physicist's argument. Let's say it has a radar-type detection that can only detect how fast something is coming or going away from it. Now, if a vehicle is going at 30 mph but going around a bend, the speed detected will ALWAYS be less than 30 mph. One can see this if one looks at a vehicle moving in a circular motion. Only when it is moving in a tangential path towards where the detector is will it register the actual speed. At other locations along the circular path, the speed that the object is either moving towards or away from the detector will always be less than the actual speed.

So if this physicist was caught with a speed of 36 mph while going around in a bend, then if the scenario that I've argued here is correct, it means that he was actually going FASTER than 36 mph, which wouldn't help his case. But like I have said, it depends on how the speed is detected here. Without knowing anything more, I'm just making speculation on how this is done. Does anyone else know how such a "speed camera" work?


1 comment:

Anonymous said...

I can't tell you how a speed camera works exactly, but it should be very similar to the radar system we cops use in our squad cars. I remember at my radar certification class the instructor saying something similar to what you said above, that if I activated my radar and caught a car coming around the corner the speed will register lower than it's actual speed. The physicist would do better challenging how often the camera is tested and calibrated, or just own up to the fact he got caught speeding, pay the fine, and move on with life.