----- Original Message ---- From: Gary McGuire <gary.mcguire@ucd.ie> To: math-fun <math-fun@mailman.xmission.com> Sent: Friday, August 24, 2007 4:31:33 AM Subject: Re: [math-fun] Doppler shift and relativity On 8/23/07, Eugene Salamin <gene_salamin@yahoo.com> wrote:

Let's look at the Doppler shift in light due to the velocity v of an observer.....

I've been wondering from time to time about a different question about Doppler: Suppose you are driving along a motorway exceeding the speed limit, and you notice a cop with a speed gun aimed at you and he/she is about to take a reading of your speed. You jam on the brakes, and the reading is actually taken as you are deccelerating. How is the reading on the gun affected? Could it appear that you are below the speed limit when in fact you are above it? This happened to, er, a friend of mine who didn't get a ticket. (Of course there are many other possible explanations as to why he didn't get a ticket.) Gary McGuire The answer depends on the details of the radar gun, mainly its response time and display update time. Hard and sudden braking for no apparent reason is unsafe and that might attract undesired attention from the cop. Here's my technique for avoiding speeding tickets: Don't exceed the speed limit. Then you need not be alert for the highway patrol, can give your full attention to driving safely. Gene ____________________________________________________________________________________Ready for the edge of your seat? Check out tonight's top picks on Yahoo! TV. http://tv.yahoo.com/