One of the things that I look forward to each summer is our annual trek to the family homestead. My children love to spend time with their grandparents hiking in the woods, fishing in the pond, hunting for botanical and zoological wonders in the immense garden, and visiting with all 25 + or - grandchildren / cousins which all seem to show up at the same time!!
One of the things that I look forward to the most is visiting with my little brother (10 years younger than me!). Randy is a full fledged donut eating, coffee drinking, swing shift working policeman in our home town. Now don't get caught up on the stereotype mentioned here - I will go to great means to show that he does a lot more than consume pastries while on duty....After all, he is the guy who suddenly appears in your review mirror that strikes fear in your heart and causes an involuntary action which makes you to slam on the break pedal. Randy is not one of the T. V. stereotype "dumb" policemen - in fact very few of them are. Randy got nearly straight A's in high school and scored near perfect on the ACT .... and as I discovered has a profound knowledge of applied physics. Randy is also a certified Fireman and will be getting Paramedic certification in the near future.
When I return to my home town I look forward to the times that I get to do the "ride along" with my little brother. We respond to calls, do traffic duty, pull over speeders, and patrol the town. The particular day that I rode along this summer, Randy was assigned to help with the traffic division on accident assessment and investigation that day - an assignment that he grumbled at after leaving the briefing session, but turned out to be very educational for me. We collected a large envelope of materials (protractors with shapes and figures cut into it, a slide rule looking thing, a booklet of equations and figures, several tape measures, a calculator, a camera, etc.) and off we went.
"Patrol 35 - assist on a code 10-50 at the intersection of 17th and Center," came the call on the radio which was immediately followed up by "details on the computer." The details that were mentioned immediately showed up on the E-mail instant messenger program on the on-board computer system with all the details of the accident scene recorded from the call to the 911 dispatch center. Yes, you heard right, an on-board computer system that is hooked to a dedicated cell line / modem located in the trunk of the car (which every car in the fleet has!!) which is hooked up and running anytime the car is running allowing for continuous e-mail, internet access, access to data bases is most states, and which allows for reports to be written at the scene and transferred electronically to the main frame computer at the station. I always wondered how I could get e-mail from Randy's mobile office - now I knew - he was also a tech junkie!!
Now, this is the cool part.
This lady had been traveling at an undisclosed speed and was not paying attention as she
rear ended the car in front of her which was stopped at the red light. Once the people had
been attended to by the paramedics (both of which were taken to the hospital with minor
scrapes, cuts and bruises) Randy went to work. He got out a camera and immediately took
pictures at multiple angles (he said this was more for the insurance companies than for
himself!!). Then he got out a measuring tool which he ran the length of the skid mark. He
pointed out some very interesting things, like "see that jiggle there in the skid
mark - that was the point of impact" and "look a the even breaking pattern -
this will be an easy one to figure out." He then pulled out a little "cheat
sheet" of equations and began plugging in numbers at the end of which he said that
her initial breaking speed (which he described as point of perception) was around 30-35
mph. And she was still doing about 15 mph at the point of impact. He then took out a
template and traced little car figures onto a blank piece of paper, recorded the
individual measurements and car positions of the scene. Then the tow truck hooked up the
cars and hauled them off!!
OK - I was fascinated by the paramedics, tow trucks, glass and the fact that I got to
direct traffic for about 5 minutes, but what really impressed me was Randy's ability to
figure out the speed of initial breaking and impact??? He was always bright, but I had to
figure this one out. So we took a lunch break (and no - we didn't have donuts and coffee!!
- we had a salad and a diet soda at a curb side café.). During lunch Randy educated me in
car accident physics or Kinematics.
Kinematics is the application of basic equations of motion to traffic accident reconstruction (Fricke, 1994) "The branch of engineering mechanics which deals with the motion of particles, lines and bodies without consideration of the forces required to produce or maintain motion is called Kinematics." Fricke explains that there are three basic equations to illustrate this application:
There are multiple pages of equations to establish each of the variables (unknowns) as listed above (refer to Figure 2) (Fricke, 1994).
Randy used the equation which states that the speed at the point of perception is equal
to the reaction distance (skid mark) plus the speed calculated by the skids prior to
impact. The speed from the skids is 5.5 times the square root of the drag factor (the drag
factor is a set of calculated measures determined by the surface composition and
conditions of the road surface). Once he calculated point of perception, he was able to
plug that value in as vi in the algebraic equation and calculate impact speed
(or end velocity). No big deal!! OK - Randy is also a mathematician and applied physicist
- not to mention his ability to problem solve and use both inductive and deductive
investigative abilities. I could just hear him quote Sherlock Holmes.... "Quite
simple my dear Watson, you see ...."
Well, after a fine day of multiple car accident investigations - and a day full of learning the application of Kinetics, I had a new appreciation for my donut eating, coffee drinking, swing shift working, techno junkie, applied physicist, problem solving, and very intelligent little brother - officer Randy!!
That
was a great experience, but the demise of Old Red really brought the whole experience
home. One evening John Cannon and I were having one of our regularly scheduled EJSE
editorial meetings, splitting a bottle of fine wine, when we heard a terrible noise in
front of his house. The noise began as a low grumble which accelerated into a very loud
squeal and ended in a terrible smashing sound (I know physics of sound!!) Anyway, it turns
out that a brand new Chevy Tahoe, carrying several underage intoxicated teenagers, had
lost control of their vehicle and had slammed into John's 1967 Chevy Pick-up truck (Old
Red). Of course the police responded immediately and amongst the tears of terrified kids
in handcuffs, very upset parents, sirens, emergency folks running everywhere, one officer
began the investigation...Kinematics.... The skid mark measured over 120 feet, the point
of impact was marked, and the officer quickly estimated that the point of perception was
approximately 70 mph!! Speed of impact was officially "undetermined" due to the
fact that the vehicle had turned sideways and had an irregular impact impression / skid,
but was said "unofficially" to be somewhere between 25-35 mph. And that ended
the last EJSE editorial meeting and created the demise of Old Red!! (which John then sold
to the wrecking yard for a whopping $50.00!!)
I wrote this editorial for several reasons, but the most important reason for us as science educators is to understand that all of our students will have application for the science which we teach them. We may not fully realize this now, but in the case of my little brother, he has a career of applied science as a police officer - as does a chef, a bartender, a construction worker, a farmer, etc. We just need to realize the science involved in these occupations and make it visible to our students so they realize the importance of understanding basic science and its application to the real world!!
Welcome to the 4th year of the EJSE, we hope that you enjoy reading the articles and as we enter into the next millennium we will continue to bring you quality research in a technologically advanced venue for FREE!!
Dave Crowther
Oct, 1999
Reference
Fricke, L. (1994). Traffic Accident Investigation Guide. National Highway Traffic Safety Adminsitration (NHTSA). Northwestern University.