Thorn Consulting Services - Certified Accident Reconstructionist

Momentum Analysis

Vector DiagramThe use of vector sum analysis plays a very important role in accident reconstruction. To understand vectors and their components is to understand momentum. A vector diagram is a way to draw a visual representation of the dynamics of the collision. It also allows you to calculate the impact speeds. You may be asking yourself, "If I can solve it mathematically, why bother with this?" Remember, you may have to explain how you came about your conclusions to a jury. I am sure that a fair percentage of any jury would be comprised of "visual learners". There have been a few notable trials in recent years where the jury has returned a not-guilty verdict, possibly because the scientific evidence was not understood. Now imagine spending over an hour explaining to a jury how you mathematically calculated the impact speeds for two vehicles and what sine and cosine mean. Do you think that you may lose the interest of a few of your jurors? To be honest, when you have to explain some of this stuff to people, it can get pretty boring. Vector diagramming is a way that allows you to visually represent the collision and easily explain it to jury.

In addition, the vector diagram will help you determine what the delta-V (change in velocity) and the principal direction of force (PDOF) are. This "change in velocity" experienced by the vehicle, and its occupants, is what determines the severity of the collision and will act along the PDOF. The delta-V correlates well with serious injury and fatality collisions. Emergency room doctors are very interested in the delta-V experienced by their patient. They know if the delta-V is high enough they can expect to see life threatening injuries. The delta-V can be calculated mathematically and through a vector diagram.

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