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How to work out the impact force of a colision

  1. Dec 14, 2014 #1
    Hi :)
    Here is a true story... I was in my car which weighs 820 Kgs,
    I for arguments sake weighs 80Kgs
    and the vehicle has an acceleration of 0-100 Kph in 15sec
    I was at a stop and went to go around a stationary vehicle in front of me..
    I locked the wheel and attempted the pass but instead made contact with the vehicle in front.
    I calculate that I must have been less than 1 meter from the vehicle in front as if it were any further from the vehicle I would not have made contact... there was very minor damage to both vehicles on close examination.
    Later my insurance company called and said that I was being claimed against for personal injury by the driver of the car in front which I had come in to contact with... yea I know!!
    So my question is... what was the force of the impact?
    and how much energy was released in the collision?
    I have looked at the formula of E = 1/2 m v2 but am not sure if I am applying it correctly..
    Can anyone help?
    Many thanks
    Mike
     
  2. jcsd
  3. Dec 14, 2014 #2

    mfb

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    The force depends on the way the cars get damaged.
    The acceleration depends on the velocity (and how fast you actually accelerate), so that number does not help.

    With cars (in general), it is possible to reach a speed of a few meters per second within 1 meter. If you tried to make a sharp curve, I'm sure you did not go for maximal acceleration, on the other hand...
    An inspection of the damage by an expert should give a more accurate estimate for the velocity.
     
  4. Dec 14, 2014 #3

    Danger

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    Hi, Mike. This type of question has been raised here at least a dozen times that I can remember. The answer is always the same. For any official purposes, such as court cases, the only acceptable course of action is to hire a professional accident reconstructionist. It absolutely cannot be done over the net.

    edit: Hi, mfb. You sneaked in while I was composing.
     
  5. Dec 14, 2014 #4
    Thanks:)
    I read that velocity only applies to moving in a straight line, that in a curve you increase in speed but your velocity changes.. I think that was the gist of it anyway.
    Yes I'm sure that an expert will know but I would love to be able to work it out for myself..
    I kind of thought that with an acceleration of 0-100kph in 15 seconds from a standing stop would give an approximate velocity of 1.3meters per second or so...
    If I was traveling fast and from a long distance I'd say that the numbers would be tough to work out without being accurate but at a meter distance and low velocity the realms of probability I'd hope could be found lol
     
    Last edited: Dec 14, 2014
  6. Dec 14, 2014 #5

    Hi and thanks for replying Danger... yea it is being handled by the experts but its more the spark for an answer to the question for myself that I am curious about at this stage.... applying the mathematical formula and so on you know..
    But yes there are people for whom this is bread and butter so as I say its more for my own personal reference than for legal purposes
     
  7. Dec 14, 2014 #6

    mfb

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    Well, cars are able to get a few meters per second over one meter, that mainly depends on the friction between tires and street.
    The acceleration is limited by friction for low speed and by motor power for high speed.
     
  8. Dec 14, 2014 #7
    Ah I see.. so its not just a simple case of knowing what the vehicle is capable of, but also the means by which its travelled.
    never thought of that
     
  9. Dec 14, 2014 #8
    Its interesting I read that when a projectile strikes something energy is released in the form of sound and heat, yet this energy was diminishing with distance and some was transferred through the air as a shockwave so to speak.. then some energy created by the engine and the subsequent friction by the tires on the surface meant that the vehicle itself depending on the surface would possibly have performed in efficiently
     
  10. Dec 14, 2014 #9

    The more I think of your mail the more I say to myself that I perhaps am not welcomed in posing such a question?
    To me it is exactly real things in life that serve as catalysts for people becoming interested in science and wondering how people as great as Sir Isaac Newton came up with the laws he did and how we can apply them today.
    I appreciate that this site is probably a high level physics discussion forum but I also feel then if that is the case the question I posed would have been easily answered.
    I suppose I was hoping that someone would engage me and have the passion for the subject enough to educate me on the various variable that come in to play and how they interact with one and other.
    I know that you probably get people coming on here all the time asking the same lame questions and so on and that its old news to some of the brilliant brains that are on this forum but to me these are new things and I am trying to lean about them.
    Mike
     
  11. Dec 14, 2014 #10

    mfb

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    Car collisions depend on the way the cars were moving before the collision. That shouldn't be surprising.
    Your car is not a bullet going at supersonic speed.
    I don't understand that part.
     
  12. Dec 14, 2014 #11

    Danger

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    That is absolutely not the case at all. Of course you're welcome to ask things like this, especially if you are trying to learn about the subject as well as just being curious.
    Most of the people who have asked this sort of thing before have done so because they intended to treat our answers as "expert testimony" in court or in arguments with their insurance providers. I was merely pointing out that doing so is a waste of time, because a court will not accept it. They require someone with credentials that they can put on the stand to cross-examine. A proper determination of the details involves such things as physical examination of the scene for such things as road surface, crush characteristics of the vehicles, and other variables that cannot be determined via computer.
    I'm sorry if I made you uncomfortable.
     
  13. Dec 15, 2014 #12
    I'm trying to see the relationship between energy put in and energy that comes out or is lost...
    Sorry I'm not explaining my train of thought correctly... Just thinking to myself that if a burst of energy occurs then after the fact its all down hill from there for it, in its purest form.. I mean its being lost through transformation either with heat that then cools... force that is absorbed or sound that then dissipates.. . god I hope that I'm understanding this right... the same way when a bullet is fired from a gun we see the flash then the shockwave then hear the sound... and as the bullet travels its energy is lost through resistance from the air and gravity and its slows...
    A poor example perhaps but when the bang occurred in my cars engine the wheels turned but depending in how clean my fuel was, depending on how new my tyres were or what else the car might have been laden with or if sufficient traction was found from the roads surface, wet or dry, asphalt or gravel... even if there was strong gusts of wind that day which created a head of tail wind, which like my engine not transferring optimum power or my tyres not gripping or the wind aiding my acceleration.
    I suppose I'm thinking to myself my god exactly how much energy is there out there when everything we have or will ever have has come almost exclusively from our sun..
    and when I read things like 1 Joule is equivalent to 1 Watt per second... or equivalent in energy to that of a baby crawling... then I look at the bottom of my kettle and I see that it takes 3.5KW going for 5 minutes just to make myself a pot of tea... then I say holy god is that the equivalent of 360Kg being pushed a meter a second for 5 minutes just so I can crack out the chocolate biscuits? what the hell are we doing with this resource that is so inefficiently used by us.. how wasteful we are
    I hope Ive not lost you with my ramble..
    I thought about you saying how friction effects more at low velocity and that's it engine power then that impedes at higher velocity and just wondered about the trade off
     
    Last edited: Dec 15, 2014
  14. Dec 15, 2014 #13

    Thanks for replying to me.
    Its not your fault that I felt uncomfortable more my own feeling of inadequacy where hard scientific facts are concerned in posing a question to a community that I am unfamiliar with.
    I suppose I'm just tired of being inspired by the Discovery channel and thought I might as well actually swallow my anxiety and actually try and throw myself to the wolves as it were...
    To folk on here I'm sure the topics and discussions are just part of their every day existence, things that are outside the purview of the majority of those who live on this planet... but that are real and influence the lives of us all and very existence of everything we know and for those who follow us..
    I went to a Christian brothers school where blind faith was required for more than just religion but also for science and mathematics... there was no practical learning whatsoever.. and if truth be told we were more likely to get a bang of a book then we were to have the opportunity to understand what filled one.
    You're dead right about not trying to jump into deep legal waters though when attempting to argue a legal case.. for that I think you do me a favour in suggesting I use what I may learn here as just that, learning... and not try to become an overnight crash expert... point taken.
    No... thank you for giving me honest guidance and splitting the topic between that of learning and that which is legal.
    I wont deny that I was slightly intimidated coming on to this forum as I have no experience with this kind of thing and actually when I did a search for similar topics like you said there were loads of questions like mine were posed and really I should have been more patient and just looked harder for a similar scenario and reply as there are definitely a lot.
     
  15. Dec 15, 2014 #14

    Danger

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    No sweat. I started here by making a couple of jokes in serious threads, not realizing how elite the site is (I stumbled across it by accident in a Google search), and was redirected to the General Discussion forum where I spent most of the next few years. I never finished high-school, but it gradually dawned upon me that I actually knew a few things (in some cases things that no one else did). It gave me a sense of purpose, but I still hang out in GD being a smart-ass most of the time.
    Believe it or not, this is the only forum that I've ever visited. I'm terrified to enter one on Adventure Quest even though I have questions/suggestions/complaints about the game that aren't covered in the FAQ's or Encyclopedia as far as I can tell.
     
  16. Dec 15, 2014 #15
    Adventure Quest... ha ha.. brilliant! I'd keep my head down if I were you lol... :)
    Yes elites are elites for a reason and rather then slowing them down to my level I would much rather try and catch up.. even if its just for that fleeting moment lol...
    But I think that like they say if you play a better player you become a greater player yourself at something.. similarly I'm hoping if I can hang out with a few great minds and maybe catch them in good humour I may just manage to acquire a little insight into something that which previously I might have been fearful to question or enquire about..
    One of the things that always stopped me from getting into things was because of a poor start in academia, then thinking it too late by the time I realized that some of this stuff is actually quite interesting... hmm I'd say to myself it doesn't really matter in my everyday grind of life... but as we both know that's not true at all.
    So I have a choice, I can either keep being bugged by these tiny threads of knowledge that I keep pulling at which seem to only lead to mazes... feel scared and not try to get anywhere... or else grab the thread hand over hand till I drag myself through it :) I'll try to keep my mitts to myself as to not drag anyone with me I promise lol..
     
  17. Dec 16, 2014 #16
    Automobile collisions are very complex, a lot of non-linear things going on. You start with KE = (1/2)(mV^2), of course. But that only works for rigid bodies. Cars are not rigid. That KE must be dissipated somehow, someway. The angles of collision, friction of tires (tyres) on the road surface, crumple zones of cars, sqooshiness of bodies and bodies sitting in urethane foam seats, coefficients of restitution...the list of factors is very extensive. As Danger implies, you get what you pay for here on the internet. I suspect that the legal, auto, and insurance industry have developed standardized analysis methods for collisions (and their subsequent debate in courts of law) that have degraded into limited set of acceptable outcomes. The Tag-ee Plaintiff gets a stiff neck, the lawyers get their fees to limit the award settlement, the insurance companies pay up a reduced amount and gain an agreement to no further litigation, the Tag-er Defendant's insurance is denied or get increased rates. Modern Society at its best.
     
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