Help with Doppler effect radar question.

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Discussion Overview

The discussion revolves around a participant seeking assistance in contesting a speeding ticket, specifically questioning the application of the Doppler effect in relation to radar speed detection. The scope includes conceptual understanding of the Doppler effect, its implications in a real-world scenario involving multiple vehicles, and the potential inaccuracies of radar measurements.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • A participant questions how the Doppler effect might influence the accuracy of radar readings when multiple vehicles are present, suggesting that proximity to other cars could lead to errors.
  • Another participant emphasizes the need for evidence to prove that another vehicle was speeding, implying that the radar reading may not be solely attributable to the participant's speed.
  • There is a discussion about the specifics of the speeding citation, with one participant clarifying that they were cited for 71 mph, which is 6 mph over the limit, and speculating on the reasons for being singled out by the officer.
  • Concerns are raised about the reliability of radar guns, with one participant expressing skepticism about their accuracy and suggesting that calibration issues could be a factor in contesting the ticket.
  • Another participant mentions the possibility of discussing the ticket directly with the officer, suggesting that a polite conversation might lead to a reconsideration of the citation.
  • Participants express differing views on the likelihood of successfully contesting the ticket based on the physics involved and the circumstances surrounding the traffic stop.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the accuracy of the radar readings or the effectiveness of using the Doppler effect to contest the ticket. Multiple competing views remain regarding the validity of the speeding citation and the potential for errors in radar measurements.

Contextual Notes

Limitations include the lack of evidence regarding the speed of other vehicles, the specifics of the radar gun's calibration, and the assumptions made about the Doppler effect's influence in this context.

Ingrid12345
Can any of you help. I am trying to fight a speeding ticket with a written declaration. To be honest I feel it was so unfair I was going with the speed of traffic and marked me as going 6mph more. I am sending the court explaining how I believe this was wrong and a radar error. Taking Physics 101 in college and not really good at it as I'm just learning but feel like I can win if I explain this correctly.

If my wave velocity is 71mph, Source of velocity is -1 (being the cop with his gun) what would be my source of frequency f0 ?

Also does is makes sense that the doppler effect is affected if there's other cars so close and around me and therefore his gun is inaccurate? I'm traveling in a caravan with 5 cars behind me and 4 cars so close in front..

I hope I win this court battle as I'm a good citizen and feel so unfair. 65mph limit and I was going 71mph. Plus I'm a broke college student.
 
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Ingrid12345 said:
Can any of you help. I am trying to fight a speeding ticket with a written declaration. To be honest I feel it was so unfair I was going with the speed of traffic and marked me as going 6mph more. I am sending the court explaining how I believe this was wrong and a radar error. Taking Physics 101 in college and not really good at it as I'm just learning but feel like I can win if I explain this correctly.

If my wave velocity is 71mph, Source of velocity is -1 (being the cop with his gun) what would be my source of frequency f0 ?

Also does is makes sense that the doppler effect is affected if there's other cars so close and around me and therefore his gun is inaccurate? I'm traveling in a caravan with 5 cars behind me and 4 cars so close in front..

I hope I win this court battle as I'm a good citizen and feel so unfair. 65mph limit and I was going 71mph. Plus I'm a broke college student.

Trying to discuss Doppler math isn't going to help. You would need to be able to prove that some other vehicle near you was the one that was going faster than you were, and that vehicle should have been the one to get the ticket. Did the officer write you for 71mph or 77mph? How did he single you out of the line of traffic? Perhaps it was for your speed from a time before you joined that line?
 
Berkeman NO! it was 71MPH he cited me for 6mph more than the speed limit. He said I touched the center divider line, I think that's why he singled me out. Plus it was superbowl Sunday so they were pulling over everyone and their grandma.
 
Ingrid12345 said:
Berkeman NO! it was 71MPH he cited me for 6mph more than the speed limit. He said I touched the center divider line, I think that's why he singled me out. Plus it was superbowl Sunday so they were pulling over everyone and their grandma.

But I got the feeling from your OP that you said you were actually doing 71mph...?
 
No I wasn't...but he marked that on my ticket. It was the car in front for sure...
 
Ingrid12345 said:
No I wasn't...but he marked that on my ticket. It was the car in front for sure...

Ho fast do you think you were going? And I thought you said all the cars were basically going the same speed...
 
I was about 65mph so was everyone else but the car in front was going a bit faster and as soon as he saw the cop parked pushed the breaks...but I don't have any evidence for that ;(
 
Call up the officer that issued the ticket and ask to meet so you can discuss the ticket. They WILL meet with you over the matter. Be nice, talk to him about it, plead your side of the story, perhaps he will understand that a mistake could have taken place and drop it.

The majority of reports that I have read about people beating the Lidar gun in court all boil down to the guns calibration dates being wrong. Though, I don't know where one would go to get that information after-the-fact.
 
Ingrid12345 said:
I was about 65mph so was everyone else but the car in front was going a bit faster and as soon as he saw the cop parked pushed the breaks...but I don't have any evidence for that ;(

Sorry, I don't believe you. Radar guns are not that inaccurate.
 

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