Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Figuring out force.

  1. Dec 30, 2009 #1
    Hi, I'm a person that likes physics a lot, but I'm unsure of how to address this problem I'm currently facing.

    I was recently in a car wreck, and am backing myself up with evidence to go to court with. A woman hit me in the back right side of my car, and I'm not sure how to calculate the force of her car that was transferred to mine.

    Okay. So I'll give you the givens, I suppose.

    In this situation, I am A, the woman is B.

    Okay, so the explanation is somewhat difficult.

    The woman stopped at a stop sign, and then accelerated her car to go across an intersection, and into a parking lot. I was driving 25 mph through that parking lot, in a perpendicular direction to where she was going. The distance she travelled before she hit my car was about 50 feet.

    My car spun a full 90 degrees. I'm not sure how to calculate the distance of that, my car is about 14 ft long though.

    Her car weighs 1888kg, plus two 60 kg passengers. 2008 kg total.
    My car weighs 1094kg, plus one 60 kg passenger. 1154 kg total.

    I'm honestly not sure about how fast she was going when she hit me, but the frame damage suggests over 20 mph. Lets say 25 mph.

    I'm a bit rusty on my physics, but wouldn't that be about 25100N of force, with an average acceleration of 18.3 fps?

    If I'm wrong, please correct me.
  2. jcsd
  3. Dec 31, 2009 #2


    User Avatar
    Gold Member

    How much force is involved at any point in time is dependent on many details. The amount of force involved is not an informative piece of information.

    For example:
    If two marbles hit each other their time of contact is very very short, since marbles are very very hard. So in a marble-marble collision there will be an enormous spike in the contact force. In contrast with that: in today's cars the bodywork is designed to deform a lot on impact. The deformation elongates the time of contact. There is still the same amount of change of kinetic energy, but the impact is spread out over a longer interval of time, which gives a correspondingly lower maximum force.

    The issue is: which details give useful information?
    Amount of sustained damage is informative. Amount of displacement (spinning around) is informative. A guestimate of the maximum force is not informative.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook