08 - The Case of the Speeding Ticket
Holt ~ Energy of Waves
Critical Thinking
You receive the following e-mail from a friend:
Last night I was driving home when suddenly I heard sirens and saw flashing
lights. Moments later, Officer Laura Biden told me I had been driving over the
speed limit. I was surprised to hear that. Just a few minutes earlier, my
speedometer had shown that I was driving below the speed limit.
When I told Officer Biden that I didn’t think I was speeding, she explained to
me how police radar works. The radar sends out high-frequency radio waves that
bounce off of the automobile. The waves are reflected and then received by a
recorder. The recorder measures the difference between the frequency of the
wave that was sent and the frequency of the returning wave.
This explanation sounds convincing, but I don’t understand it. I don’t know
which to believe—my speedometer or Officer Biden’s explanation. How can a
car’s speed be measured by the frequency of a wave? Is police radar always
accurate? Please help me determine whether I was speeding.
Lou Pole
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