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Question on calculating speed

  1. Jun 8, 2010 #1
    Can someone explain to me how to calculate the speed of an object on a video.

    I was involved in a car accident last week that was captured on my office security camera. The car that hit me is perpendicular in the film. The video is choppy, so real time is not possible, therefore I've not been able to use the standard distance/time. The police and insurance company have told me there is no way to prove the speed at which the car was traveling. I don't remember much from physics class (long time ago) but know there has to be a way.
  2. jcsd
  3. Jun 8, 2010 #2


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    Staff: Mentor

    You just need the frame rate of the video, and you can estimate the distance by knowing the length of the car.
  4. Jun 8, 2010 #3
    If the video has a timestamp with milliseconds or hundredths of seconds or a constant framerate, you can calculate the speed with enough accuracy. Estimate the distance of a specific point on the car between two frames and divide it by the time between the frames you are comparing. Of course you would have to convert the measurement from feet (or meters) per second to miles (or kilos) per hour.
  5. Jun 8, 2010 #4


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    Gold Member

    Why? This is what they do.
  6. Jun 8, 2010 #5
    Because it's easier & cheaper to just pay off the claims.
  7. Jun 8, 2010 #6
    Thank you for responding. I know there are much more interesting threads on this forum. It's been very informative looking around this board, it makes me want to learn more so I can understand them.

    I will try to figure out at what rate the video recorded and look up the length of the other person's SVU.

    My car was 3 months old, with less than 5 K miles on it. My state is no fault unless one of the vehicles is breaking the law. I'm motivated for several reasons: one because everyone keeps saying the calculation can't be done (do I hear a challenge ?). Another, I estimate the other car was going at least 60 in a 45 and was less than 4 seconds from a 25 mph school zone. I tried to accelerate from 25 to 45 in a fuel injected 6 cylinder car today in 4 seconds and made it to 30 max.
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