What Is the Role of Physics in Collision Reconstruction?

[CuriousCop]

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Hello all,

First off, thank you for taking time out of your no doubt busy schedules.
A little background, I am a police officer in SC. . . . .yes I can hear the wheels turning in your brains.
I have a run of the mill Associates Degree and working on a Bachelors.

This being said, I am without a doubt clearly not as smart or educated as most of you on this forum( it is very difficult not to type "ya'll").

Please forgive my grammatical errors and have patience with me. I am here to learn more about everything in the physics world. I have recently found a love for astronomy, quantum physics ( my favorite is field theory but that may be bc its easiest to wrap my brain around and Sean Carroll is very adept at explaining things well in his lectures).
I am part way through becoming a certified collision (vehicle) reconstructionist and have used math that I never thought I was able to understand. I realize that this is simple physics(drag coefficient, force and mass equations, classical Newtonian mechanics) but I find it exciting!
I would have never thought that the feeling of completing a math question with 5 pages of equations to find a few simple values would feel so fun!

I look forward to learning from you all and maybe asking some questions if permitted. Thank you for your time and attention to this and please feel free to ask me anything(physics related or police related).

-Hoyt

 

[fresh_42]

Hello and !

Finally we will be able to actually name an expert!

I am part way through becoming a certified collision (vehicle) reconstructionist

You could imagine that we often get questions in that direction, and of course we cannot answer them for several reasons: not enough information, wrong platform, legal issues, and so on and so on. We always recommended to search for a local certified person. Soon we will have a member who is!

Have fun and stay curious!

P.S.:

...yes I can hear the wheels turning in your brains.

Doesn't matter, we have a strict "no politics" rule.

 

[CuriousCop]

Thank you! Lol my wheels turning remark was more aimed at the thought that some may have that I am a poorly educated regular guy, which is mostly true.
I will say that I appear to maybe have an aptitude for more of the cerebral things than most of my coworkers, but I am not beyond being a knuckle dagger every now and then.
Thank you again for the kind reply! I will always attempt to be available for answering any questions, about my work, legal aspects, physics we do for collisions, aspects of data collection, how cool it is to drive fast, what equipment I carry ect.
I am also a certified radar and lidar smd(speed measurement device instructor) so I have a rudimentary understanding of the electromagnetic wave spectrum and doppler principle as it pertains to those devices.
I am also in the SWAT team and a breacher/entry team member, so any physics related questions( or resllt anything the mods allow and my department policy will allow)ill be more than happy to answer.

Alas, as a sign of my mediocrity, I edited my first intro and it dissapeared, thus leading me to believe it lost. I made a new intro, found a grammar error, edited it and it dissapeared, then it dawned on me that when I edit somthing it may pend a review.
So I apologize for my probably 2 similar intros. The second being a bit more polished. . . .. .yup I'm a dummy sometimes and I'm alright with it if it makes you all smile every now and then ( :

 

[fresh_42]

Ok so I'm not sure if this will be a double post. My original introduction disappeared after I posted it. I apologize for any confusion on my part.

I merged the two. It wasn't your fault. Some threads are going into moderation automatically. I think because of certain keywords or attachments, but I couldn't figure out a scheme yet. I approved your previous thread (post #1 above), and answered (post #2) only to find it on moderation again. So I approved it for the second time. We'll see for how long it will last this time ...

 

[CuriousCop]

I merged the two. It wasn't your fault. Some threads are going into moderation automatically. I think because of certain keywords or attachments, but I couldn't figure out a scheme yet. I approved your previous thread (post #1 above), and answered (post #2) only to find it on moderation again. So I approved it for the second time. We'll see for how long it will last this time ...

Thank you so much! I apologize for that. I will try very hard not to disrupt and be very cautious of words I use. I do not wish to offend anyone and I have absolutely read the rules. I am here to learn and also to contribute as much as I can, in any way. I won't be leading the way in quantum gravity anytime soon but I believe I can be helpful to some and I hope to find clarity on some field theory questions in some of the forums. Thanks again!

 

[CuriousCop]

Hello and !

Finally we will be able to actually name an expert!

You could imagine that we often get questions in that direction, and of course we cannot answer them for several reasons: not enough information, wrong platform, legal issues, and so on and so on. We always recommended to search for a local certified person. Soon we will have a member who is!

Have fun and stay curious!

P.S.:

Doesn't matter, we have a strict "no politics" rule.

Yes I was pleasantly surprised at the amount of police radar( and lack of lidar) questions asked and I am finding out that teachers and professors like to use a speeder and police car type scenario as the basis for some homework questions.
Now they always seem to be missing the friction coefficient of the roadway, median, ( as in a multi surface speed combination for the police car, as we usually sit in a grass median so our tires start in the grass the move to the road). So I am excited to contribute to these scenarios.
Being mainly a traffic officer, I do a lot of that for a living.

 

[fresh_42]

I guess a lot of accidents especially by young people could be avoided if they had a better understanding of physics. I remember I once replied to someone who put new tires on my car as he complained how little people care about their tires: "This rubber is all that keeps me on the road!"

 

[CuriousCop]

I guess a lot of accidents especially by young people could be avoided if they had a better understanding of physics. I remember I once replied to someone who put new tires on my car as he complained how little people care about their tires: "This rubber is all that keeps me on the road!"

Absolutely! People(most) have no idea that it is only a few inches of rubber that contacts the road. That small amount of rubber controlling the incredible forces acting on and coming from the vehicle is scary.
On a sad note, the more fatalities one works, especially when it involves teenagers, the less you start to feel bad about writing a citation to someone for speeding. I will say that if you wear your seatbelt, it's amazing what you can survive. Most deaths I have had the unfortunate duty of working, could have been avoided with a seatbelt and a minor reduction in speed. Past 45 mph, force starts to increase at an alarming rate. At that speed and above, 10mph of speed does not equal a similar increase in force.

On a positive note, viewing some of the threads, I have already learned an applicable fact about how force is transferred at the speed of sound through solid objects( the ole faster than light communication via an incredibly long stick thing). Fascinating! I'll be turning some of my coworkers on to this forum.

 

[fresh_42]

At that speed and above, 10mph of speed does not equal a similar increase in force.

Yes, energy goes with the square of speed. I remember I once had to brake from 160 km/h down to 100 km/h on a short range. This was definitely different than stopping a car from 60 km/h.

We have a certain kind of accidents here, I call them disco-accidents. Ingredients: one or two male youngsters, filled with testosterone, usually with some alcohol, too, one or two girls. Saturday night at the disco, monday morning in the local news.

 

[CuriousCop]

Yes! It's difficult for someone like me with no physics background when we get to recon class phase 1(the first of 4 classes, that are 2 weeks each) and see that speed and force aren't directly proportional.
Then you add in speed loss when braking over different surfaces, flips and vaults, momentum in and out(that one actually isn't bad lol) and our brains started to hurt.
I suppose it's far easier than a general physics course though as we are learning a single specialized set of equations and how to apply them to find certain values applicable to a set list of legal questions about a vehicular collision.