Question of vehicular safety
Question of vehicular safety
(OP)
I've been having a discussion with my wife regarding the safety of automobiles. My wife hit a deer today with her car and later made the comment that it's a good thing the car didn't crumple like an accordian. I tried explaining that the crumpling is what makes the car safer to the passenger because it helps to dissipate the energy of the impact as well as decelerates the car at a slower rate (which, in turn, imparts less acceleration and force to the passengers). She is convinced that a car that could make it through a head-on collision with no damage is the safest car to be in (while I told her that is actually the most un-safe car to be in) Let's for argument's sake say a 1970 chevy nova is in a collision with a 2010 toyota camry - she believes the passengers in the nova will make out better. She suggested I come here to pose this question. I already know what the answer is, but I would appreciate if some of you could weigh in.





RE: Question of vehicular safety
The goal is - as you correctly noted - to dissipate the energy of the collision in a controlled way. The reduces the deceleration experienced by the occupants.
The super stiff car subjects the occupants to much higher decelerations and corresponding injury.
The 1970 Nova might crumple in an uncontrolled way, including deformations that reduce the survivable space in the passenger cabin. Uncontrolled crumpling is bad.
Numerous sophomore or junior engineering design competitions involving eggs demonstrate this.
RE: Question of vehicular safety
Perhaps she should ride in a car with no shock absorbers or springs to experience the instantaneous accelerations to her body, then ride in one with them to see which ride she prefers.
No different in an accident. Any energy that anything in the accident absorbs rather than transfers, is less energy your body has to deal with.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Question of vehicular safety
She probably wouldn't even notice the impact.
Or if she were driving a big rig.... big rig drivers also have been known to wipe out a passenger car and not notice.
JMW
www.ViscoAnalyser.com
RE: Question of vehicular safety
might show her this one (59 bel air vs 09 malibu)
http://www.youtube.com/watch?v=joMK1WZjP7g
RE: Question of vehicular safety
Here is one you don't want to be in ...
http://www.youtube.com/watch?v=8kuSghb7P7U
Here's what happens when a new car hits an old one ...
ht
Take particular note of the interior views. The interior of the new car is hardly deformed. The old car is quite another matter.
Here is another good one comparing a modern vehicle with an older one.
http://www.youtube.com/watch?v=uvoumToSP5c
RE: Question of vehicular safety
The most valid collision scenario is one between two identical vehicles. Two identical, rigid vehicles produce a less survivable collision regardless of mass. Mass becomes irrelevant - it is the deceleration distance (crumple dimension) that determines the magnitude of the deceleration the occupants are subjected to.
RE: Question of vehicular safety
Kinetic Energy = (1/2)mV^^2
So for unfortunate Bambi crossing your path, the KE is almost zero. Versus your poor car buzzing along at 45mph...no contest. Masses AND velocities come into play. Some of the modern weaponry these days rely heavily on the V^^2 component to deliver enough KE to damage a target sufficiently. Think of the NATO 5.56mm round.
Then also, remembering "Conservation of Energy"...all that KE(car1) and KE(car2) must go somewhere. Hopefully car1 and/or car2 can take all that KE and turn it into mechanical deformation energy and heat. But usually there are some other components of re-directing one KE vector into another KE vector, which produces those abrupt changes in momentum ("accelerations") that snap necks and such. Think of Dale Earnhardt's accident when he hit that wall at almost 200mph. Now most all them boys wear those collars.
TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com
RE: Question of vehicular safety
RE: Question of vehicular safety
First, you are arguing with a non technical person. I make this assumption based on her position in this case. A technical person would know better right off.
Second, you are arguing with a woman. Sorry, but to most of them that I have ever met, logic and facts mean nothing, emotions mean everything.
Lots of good and valid information has been presented here by experienced professionals, but I don't think it will matter a twit to further your case.
The operative words are "Yes Dear, you were right, I am sorry." Then go to work and impress your technical buddies with your technical gleanings from this thread.
And hope she never gets in a head on collision.
rmw
RE: Question of vehicular safety
- Steve
RE: Question of vehicular safety
The second was I asked her to put a book tight to her nose. I asked if she would rather I punched the book or rather I replace it with a pillow.
Neither of these examples got my point across.
RE: Question of vehicular safety
Newton's laws really work.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Question of vehicular safety
A stiff car collides with a soft car. The forces of impact are equal so deceleration is inversely as the masses and thus I will choose the larger stiffer car as safer against a smaller softer car, if that is the test.If the cars are of equal mass, then the decelerations are equal and there is no benefit of the softer car, but only for this test.
So your wife is not exactly wrong for this .
However if you choose to hit a tree, the reverse is true.
In summary,I'll take a tank any day for this test.
So, go buy your wife a Hummer.
RE: Question of vehicular safety
-AAFuni
RE: Question of vehicular safety
I'm right ≠ she's happy
TTFN
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RE: Question of vehicular safety
A mistake I also made in this thread....a well earned star for RMW.
This is one time the client is always right.....
This is one time when you could be IK Brunel and a world expert and win (?) the argument but lose the war....
This is also an illustration that we should be wary of being focussed on the wrong problem by the client.
In our case the client is StructuralEIT who presented an engineering problem which we all tried to solve rather than a marriage counselling problem which it really is and RMW spotted.
Listen to the rest of us and pretty soon Structural would be sitting his wife down and lecturing her with Power Point presentations and You Tube videos helpfully provided by the Eng-Tips members.... only for StructuralEIT to end up as road kill.
You are obviously in real trouble.
Offering to put a book in front of the wife's nose and punch it is not recommended. It does suggest that this has escalated already into a fairly intense argument.
The more you argue, the more stubborn she gets.
She will never ever accept the real answer (unless you can get it printed in the Sunday Supplement horoscopes).
No, a sudden reversal on your part will only make things worse.
If you've been saying "its only simple mechanics that a three year old could understand, so why doesn't she?" then you are way past "Hey, guess what, I was wrong and you were right honey."
Because if she was baring her teeth before, she might skip straight past going home to mum and on to her own experiment with you as the soft squishy animal.
Your only hope now of saving your skin and maybe even your marriage is to generate a plausible explanation that shows your wife to be right.
So, everyone, heads together and fake up a way to show, scientifically, that the wife is right, complete with PowerPoints, graphs, a hockey stick chart and You Tube videos and all planted on the internet somewhere (OK, you can create a fake web page and run it in IE6).
It can't be all that hard, I mean, look what they've been able to do with a few tree rings and a some ice cores.
JMW
www.ViscoAnalyser.com
RE: Question of vehicular safety
RE: Question of vehicular safety
For the purpose of this conversation neglect the car vs. car situation and stick to the deer situation, in which your wife is sort of right, it is best that the car didn't really get that damaged.
RE: Question of vehicular safety
Part of your problem is that your wife is looking at a specific accident, and you are looking at wide range of potential accidents. She actually is right, that a sturdy car sustains less damage when she hits a deer. This also is true for supermarket fender benders. If she hits a concrete abutment, or another car head-on, this is not true.
Think about all the people who bought SUVs because they were bigger, therefore, safer in a crash. They focused on the head-on collisions, and they ignored roll-overs, which is what makes a lot of SUVs more dangerous than cars.
Quite a few years ago, I have driving on a limited access highway at 100km/hr when a deer ran across in front of me. I was in a 1988 Honda Civic. If I had hit the deer, it probably would have gone through the windscreen, and it would have been very dangerous.
RE: Question of vehicular safety
Paging Dr. Freud...
RE: Question of vehicular safety
I think I typed it that way nearly every time and had to correct myself each time.
RE: Question of vehicular safety
I hope you took no offense to my remark, none was intended. After the thread turned to how best to extricate StructuralEIT from a tenuous marital situation I found that portion of your reply quite humorous.
RE: Question of vehicular safety
Kind of along the lines of a local "touchless" car wash ad.
She says " IF he won't go touchless - then I will" Hint - hint!!
RE: Question of vehicular safety
RE: Question of vehicular safety
JMW rocks, as ever.
- Steve
RE: Question of vehicular safety
You could stage this at some suitable wifi hotspot where you take your wife for coffee or something.
You needn't worry about how to steer the conversation around to the topic in question, just the opposite. Try and keep away from it. If your wife is like my wife, and has un unresolved "situation" a nice public place to beat up on her husband is all the prompt she needs to kick off the subject herself.
You might even try shushing her when she gets started.
That works with my wife, nothing more sure to cause and increase in decibels and an intensification of attitude.
She now has either to accept her new champion and in which case you can concede gracefully, or she will resent someone else trashing her man.... she may now attack him which means she has to reverse her position to protect you.
Your friend need not fear long term consequences, he isn't married to her so she can't divorce him, but she may be volatile enough to take drastic "heat of the moment" measures so make sure his PPE includes a stab proof vest.
JMW
www.ViscoAnalyser.com
RE: Question of vehicular safety
TTFN
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RE: Question of vehicular safety
That's from a simple model using an SDOF model of an energy absorber plus a mass for each car.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Question of vehicular safety
Agreed.
Speaking of safety, how come governments don't mandate testing cars against other cars and trucks at various speeds and angles of collision to get a REAL safety result.
Crashing cars against walls is meaningless when it comes to safety. Obviously , if they tested cars properly and reported the results accurately almost nobody would buy a SMALL car, regardless of the high marks it might receive from its socalled "crash" test.
Do you think governments are more interested in saving oil than saving lives??
RE: Question of vehicular safety
"
Complexity, cost, reliability, repeatability.
"Crashing cars against walls is meaningless when it comes to safety. Obviously , if they tested cars properly and reported the results accurately almost nobody would buy a SMALL car, regardless of the high marks it might receive from its socalled "crash" test."
I suspect that real customers don't think they'll crash head on into another car. I actually drive a smallish car, for whatever that is worth.
"Do you think governments are more interested in saving oil than saving lives?? "
No, not really. I think the crash testing came about as a way of improving the existing vehicle fleet, rather than starting from the other position, which would be answering "what is the most 'cost' effective way of transporting people"? Where 'cost' includes all aspects of vehicle operation including the cost to society of oil and accidents. I'm pretty sure a Hummer is not usually the amnwer!
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Question of vehicular safety
If you've looked at some of the videos from IIHS testing, you'll be amazed at what even a small car can survive now, compared to 20 yrs ago.
In fact, it used to be that car companies would cry foul about low test scores from IIHS, but they'd quietly fix the vehicles, and pass the following year and trumpet the results.
TTFN
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RE: Question of vehicular safety
Also, the argument for everyone having super crumpley cars is good provided EVERYONE has crumpley cars, otherwise you are going to get the self centered jerks rocking around in rigid cars ruining other peoples cars in accidents relying on their crumple zones, until of course they hit another rigid car or something solid.
RE: Question of vehicular safety
TTFN
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RE: Question of vehicular safety
I think a vehicle designed with Moose crash tests in mind may be in order. That meant Volvo or SAAB. No idea what it means today.
Supposedly 90 accidents involving cloven footed animals occur in Sweden every day. Stout A-pillars, etc.
ht
RE: Question of vehicular safety
Engineering is the art of modelling materials we do not wholly understand, into shapes we cannot precisely analyse so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance.
-A R Dykes
RE: Question of vehicular safety
RE: Question of vehicular safety
RE: Question of vehicular safety
While I completely agree trying to argue technical matters with a non-technical individual is clearly a futile battle, I sincerely hope that your second argument was a joke.
____________________________________________________
StructuralEIT,
Non-technical people can make me develop an eye twitch within seconds of conversation. It probably would be best to let this one go with your wife; I've had to bite my tongue on many subjects over the years for the betterment of a relationship.
K
RE: Question of vehicular safety
Question: Why is divorce always so expensive?
Answer: Because it's worth it.
Caveat: But only if you learn from your mistakes.
E.g. you may try to explain how the central heating system works to your first wife (see Sompting Guy's cryptic above) but you should know better than to try and explain to the next wife. Just accept that when you are hot, she will be cold and will crank the heating up to the highest setting and forget it.
When you are cold she will open the windows and let the snow in, still with the heating on full blast.
I was at a refinery in Southern Siberia when the temperature was about 30C below. Getting fed up with freezing in the pump room (a potential death trap due to all the exposed high voltage switch gear in there) I headed for the control room.
This was a couple of hundred meters away and the doors and windows were wide open. You could feel the heat roiling out from several paces away.
To be fair, it may well have been that they had no control over the massive steam pipes running through the control room but I suspect it had something to do with the fact that the control room seemed to be entirely staffed by large women.
JMW
www.ViscoAnalyser.com
RE: Question of vehicular safety
The thing that annoys me is my son seems to be following my wifes system. This is complicated by living in a desert with big temperature swings this time of year, compounded by our primary cooling being evaporative not AC.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Question of vehicular safety
JMW
www.ViscoAnalyser.com
RE: Question of vehicular safety
However, I think this time "force": the force the body will feel. The change in momentum.
THUS:
1) The Chevy Nova will undergo a change of momentum of about half of that of the Toyota. Your wife may be right and the Nova would be better off in the Nova Toyota head-to-head.
2) Also, like the other poster mentioned the soft crushing of the Toyota will be shared with Nova--but the Nova's mass will benefit the Nova alone and detriment the Toyota.
It would make things a lot simpler if everyone drove a car with less mass. The answer is higher gas prices--but no one is going win that election. Henry Ford intended his cars to be light, spartan, the fewest parts possible and all interchangeable and universal: the opposite of the current American designs.
RE: Question of vehicular safety
"It would make things a lot simpler if everyone drove a car with less mass"
Ya, the killer acceleration would be really save.
Quote
"Henry Ford intended his cars to be light, spartan, the fewest parts possible and all interchangeable and universal: the opposite of the current American designs"
Ya, so HE could make more money. But that way your basically strangling the whole industrie. Real good idea.
RE: Question of vehicular safety
Engineering is the art of creating things you need, from things you can get.
RE: Question of vehicular safety
Sorry, but the second point wasn't a joke at all; it was an opinion based on life's experiences. (One mother, one wife, 3 daughters - it is like having 5 mothers.) Men and women in general operate from different sides of the brain. That doesn't make men or women inferior or superior, just different, and thankfully so. Actually, when it comes to things like intuition I think women are superior to logical men and I am glad of it.
rmw