1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculating impact force

  1. Aug 16, 2014 #1

    I need your help, please.....this is true

    I was rear ended and I would like to know the impact force....

    I was waiting for the car in front of me to turn left, so I had my foot on my brake, I was driving a 2004 Lexus RX330......call it 3500 lbs.

    A large truck was texting and driving....and without braking ran into the back of me @ 35-40 mph.....his truck is 17,000 lbs and he was carrying another 5,000 lbs of deliveries

    After the initial rear end crash, then my car was catapulted into the minivan in front of me trying to take a left....my car was totaled from the rear, and the front collision.....

    Can someone please tell me approximately the impact force that hit me from behind? I am not an engineer, just a guy with a bunch of metal staples and stitches in my head.

    Someone, please respond. Thank you very much!
  2. jcsd
  3. Aug 16, 2014 #2


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Hi and welcome to PF.
    I am afraid that you won't get you want from PF because there is no way of knowing the "impact Force" that you are asking for. PF gets posts like yours very frequently and people are always disappointed by the answers they get.

    The first point is that motor car collisions are very complex; they are not like the more straightforward billiard ball collisions that we do in elementary Physics. The second point is very fundamental and that is that collisions are not instantaneous and there are many combinations of Force and the time for which the force is applied that will give the same outcome. There are two quantities that count in collisions and they are Kinetic Energy and Momentum - see, it's getting heavy already.

    Motor car manufacturers and road safety labs spend many millions of pounds / dollars etc. in attempts to minimise passenger injury at the expense of the rest of the car being totalled. There is a massive knowledge base and a long history of court cases and insurance claims.
    Successful court cases rely on 'expert opinions' about the likely circumstances of car crashes. There is a lot of data about speeds and damage (to cars and to people) and not much of it is indisputable (afaik - because expert witnesses will disagree very often). Photos of tyre skid marks are the best evidence of speed before impact but even those need to be presented by an 'expensive' witness and I don't think any DIY case would be worth the effort.

    If you have evidence that the truck driver was texting then you surely have him bang to rights. If the order of the impacts was a rear shunt, followed by your vehicle being pushed into the one in front then he should be liable for all the damage. Otherwise, I think it's normal for insurance companies to divvy up the claims according to their own magical rules and there is seldom much you can do about it (not in the UK, at any rate). The basic rule is that they never pay as much as you think they should and they are bigger than the customer!!
    Sorry, but I reckon that's the way it is and PF has failed you.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook