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Help with an court case

  1. Dec 3, 2008 #1
    My car was hit by a semi-truck in a very low speed accident, he was raveling perhaps 1-2 mph when he bumped into my car. I sued and the magistrate ruled against me. I am appealing the decision because the truck driver claimed he was traveling on the road way at speed when I cut him off. I know that according to physics that the amount of energy that would have been transferred to my car if he were moving at road speed would have been allot higher than the 1-2 mph he was traveling. To appeal this I will need to show that his testimony is contradicted by the physical evidence.

    My story is his 25 ton truck hit my .9 ton car, decelerating from 2 mph to 0 in about three feet. The damage was inline with this as he just smashed my bumper and dented my fender and hood. He testified that he was traveling at road speed, which would be about 30 mph, and could not apply his brakes before hitting me. He also said that the collision stopped his truck in the same distance. Based upon what I have been reading that kind of impact would have generated huge forces in excess of several hundreds of tons of force.

    A couple of questions then:
    How far would it take for a fully loaded semi-trailer weighing approx 25 tons (26.67 tonnes) to stop from 10, 20, 30 and 40 mph (16, 32, 48 and 64 kph), assuming dry weather conditions on asphalt?

    How much force would be behind that truck upon impact if he were decelerating from the same four speeds to zero in three feet?

    What other numbers would be needed to help out?

    Jeremy Brown
  2. jcsd
  3. Dec 3, 2008 #2
    also how much force would his 25 ton truck generate from a 30 mph to zero deceleration in 10, 25 and 50 feet?
  4. Dec 3, 2008 #3


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    Welcome to PF, Jeremy.
    This issue has arisen here before. Really, all that you can do is hire a professional accident reconstruction specialist to testify for you. There are far too many variables for anyone to analyze the situation over the net. Even if we could, our opinions would not be admissible in a court of law. You have to have a physically present expert witness who can be cross-examined by your opponent.
  5. Dec 3, 2008 #4

    Ranger Mike

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    Danger offers excellent advise. Hopefully this reply will adhere to the rules of this web site. I am no expert on physics. I have been in auto racing since 1966. Drag racing, stock car racing now formula car racing.
    One thing I know for a fact...its all about tire contact patch.
    It is not just a question braking distance. Besides the human element of reaction time to actuate the brake..and this is one huge variable in the over all braking distance you have many other variables. I recommend you make sure the crash expert takes into account tire compound ( a 10/20 semi tire is harder than woodpecker lips), unless new.
    Most semis still use drum brakes on the rear and discs up front and heat really kills effectiveness over time. The compound of the shoes and brake pads also add huge stopping variability. Another variable is the transmission of the truck. Automatics do not engine brake ( using engines compression ratio to slow the vehicle) as effectively as a manual transmission. Two final variables are temperature and the road surface. Fresh asphalt is really slick and greasy. Doubly so when hot. I have seen track temps over 130 degrees on a hot August day. Old asphalt is less temperature sensitive..but were there tar patches ( used to patch cracks) present or was the surface consistent.
    bottom lie is , ifin you want to go to the expense, you have to replicate the same conditions of the crash as closely as possible wit the correct instrumentation to collect applicable empirical data AND present it in as simple as way as possible to convince the target audience. Good luck !
    Last edited: Dec 3, 2008
  6. Dec 3, 2008 #5


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    :rofl: :rofl:
    Oh, man... I've never heard that one before! You can bet that I'm stealing it. :biggrin:
  7. Dec 7, 2008 #6
    Guys, this is a small claims court case not a major lawsuit. All I need is some basic information that can be mathematically proven.

    I want to show that if the trucker was driving at highway speeds, the damage to my car would have been significantly greater than the simple fender bender that occurred. I need to say to the magistrate, look his testimony is contradicted by the evidence, at this speed he would be carrying this much energy. An accident involving that kind of speed and energy would cause this kind of damage, not a dented fender, hood and warped bumper.

    I have an affidavit from the collision company stating that the damage was indicative of a low speed crash, not a higher speed one as the defendant is claiming.

    Is that possible with the data I provided?

  8. Dec 7, 2008 #7

    Vanadium 50

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    Danger is right. You need a professional, not some guys on the internet.

    Personally - and this is my opinion, not anything that I would intend as legal testimony or advice - you'll have a hard time proving that this was a collision between one vehicle at 5 mph and one vehicle at 7 rather than one vehicle at 55 and one at 57. It's possible that a profession could look at your car and determine how fast it was going when it was struck, but there's no way that someone on the internet could do this based only on your description.
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