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Question of vehicular safety
5

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

Controlled, designed crumpling, combined with a rigid cage around the passengers is what makes a safe car in a collision.

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

In any collision, there is a total amount of energy to dissipate before equilibrium state of no motion is acchieved.  There are many ways to do that...

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

2
Of course, if she was driving a main battle tank and hit a passenger car, she'd be OK.
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

as noted above, she should try dropping eggs until she finds a way to keep them from breaking.

might show her this one (59 bel air vs 09 malibu)
http://www.youtube.com/watch?v=joMK1WZjP7g
 

RE: Question of vehicular safety

You can find crash test videos on youtube that will illustrate the difference between a modern car (very stiff "cage" around the occupants with designed-in crush zones outside that) and an old one (in which the passenger compartment deforms).

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 ...

http://www.youtube.com/watch?v=fPF4fBGNK0U&feature=related

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

One reason your wife may be having trouble, is she is relating to her experience of hitting a deer. There is a big difference between hitting a deer and colliding with something having similar mass to your own vehicle. Colliding with a deer would be no problem in any vehicle with: 1. sufficient mass and 2. sufficient strength in the passenger cell. Not much need for crumple zones.

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

Besides the crumpling issue (which is correct), a few are dancing around the physics involved with a collision.  If you'll recall from that beastly Dynamics class:

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

Mortals are silly!

RE: Question of vehicular safety

3
StructuralEIT, you are making 2 mistakes.  (I am making the assumption that the EIT in your handle indicates your age to be young to some degree.)  I hope what I say here will help you.

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

... before trying to explain impact mechanics, try warming up with something simpler, like heat transfer as it relates to home heating/cooling.

- Steve

RE: Question of vehicular safety

(OP)
I tried some simple examples - here is one: I asked her if someone were going to hit her in the stomach with a bat, would she rather have a book tight to her stomach or a pillow.  Of course she goes and says she'd rather a book thinking that the person would hurt their hands when they hit it!!!  

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

One of the odder results we got from a deep dive into NHTSA crash data was that not only are heavier vehicles safer than light vehicles in collisions, as you'd expect, but also heavier variants of a given model were (slightly) safer than their lighter brethren. This is despite the fact that often these heavier variants were convertibles.

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

Maybe one vote for your wife.

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

If you have a heavy stiff car and everyone else has a crumpley small car, your car will benefit from the crumpley cars design (although not as much as if you both had crumpley cars).  As long as your wife is selective in what she hits (only small crumpley cars and soft squishy animals) the stiff car will be a cheaper choice as it will suffer less damage.
-AAFuni

RE: Question of vehicular safety

And that is why engineers get divorced, they spend too much time focussing on the problem and not the client (in StructuralEIT's case, his wife).
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

Phew!  Jmw, star for the excellent analysis of the problem, and outline for solution.  Good luck to Structural...

RE: Question of vehicular safety

Well in the collision with a deer she is right, she would be better off with a rigid car.  Colliding with something with a mass much less than the car will not kill you from rapid deceleration.  The danger in an accident with a dear comes mainly from the possibility of the deer coming through the window at you.  For this reason the ridged car is the better option as it will sustain less damage and be a cheaper repair, although it will make mush out of the deer.

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

StructuralEIT,

   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.  

               JHG

RE: Question of vehicular safety

Quote (aafuni):

The danger in an accident with a dear

Paging Dr. Freud...

RE: Question of vehicular safety

dgowans,
I think I typed it that way nearly every time and had to correct myself each time.

RE: Question of vehicular safety

aafuni,

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

If she is a blonde - like my wife --- GIVE IT UP..  She is right - always right - and DO NOT FORGET that.  because it WILL COST you in the long run - or even the short run!!!!!!!!!!

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

Yeah dgowans, I was thinking the same thing.

RE: Question of vehicular safety

Remind me never to bring this up with the ex-SO.  Maybe I can pollute our offspring with the idea...

JMW rocks, as ever.

- Steve

RE: Question of vehicular safety

Better yet would, Structural, would be if you could be "exposed" as an "incompetent" by some snooty superior engineer (a role playing friend your ongoing argument and chimes in on the wife's side (with all the material Eng-Tips can fake) because that way, he is attacking you.

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

Someone silly enough to get between an engineer and his wife will probably flail helplessly.  KISS principle applies here.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: Question of vehicular safety

zekeman, you'd actually be better off in a massy crumply car every time. Everyone benefits from more crumpliness, you alone benefit from the extra mass.

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

"ekeman, you'd actually be better off in a massy crumply car every time. Everyone benefits from more crumpliness, you alone benefit from the extra mass."

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

"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.
"
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

Actually, the IIHS has been doing its own, non-DOT testing for decades, and with each improvement in the IIHS testing came improvements in both cars and the DOT testing.  IIHS was the only proponent of crash testing against parking pillars, and corner crashes.  

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

FAQ731-376: Eng-Tips.com Forum Policies

RE: Question of vehicular safety

I always think about this sort of things in terms of acceleration/deceleration. The human body can only tolerate however much acceleration before whatever happens internally, externally (or when internal things become internal). The whole point of the crumple zone (at least as I think of it) is to elongate the period of time that the change in velocity lasts for and hence the less acceleration on the person. In a rigid car, if the car stops in 0.1s, then you stop in 0.1s (perhaps not all of you though).

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

That point is q bit moot, since all cars have to pass DOT tests, and most cars get tested by IIHS.  In both instances, getting a passing grade requires the car to have crumple zones.  Otherwise, they would get crappy results in the testing.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: Question of vehicular safety

In the early 70s my cousin whacked a deer while driving my Grandma's Porsche 911 and he was OK but the upper portion of the car was bent badly. Maybe totaled.

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.

http://www.vti.se/EPiBrowser/Publikationer/S342A.pdf

 

RE: Question of vehicular safety

Up here in Alaska, we get quite a few moose on the roads every winter. They actually have signs with a running total for the year, as a reminder to slow down and watch out.  It takes a pretty big vehicle to do anything but send the moose into the wind shield, so the crumple zone doesn't help much with it.

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

I guess she's right, if see had no internal organs at all.

RE: Question of vehicular safety

Flowers.

RE: Question of vehicular safety

rmw,

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

Some people, it seems, need to have two or three wives before they learn these lessons.

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

jmw, I understand the former soviet union was big on 'centralized heating systems' using 'waste heat' from various industrial processes to heat nearby offices, apartments etc. and that they didn't really invest in individual thermostats or temperature control of said offices & apartments - the solution being as you say to open windows.

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.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Question of vehicular safety

And speaking of divorce, Structural, we are now desperate to know the outcome.... I see you are still alive and not road kill because you posted yesterday....but....hammer is not the way to get ideas across.... and unless there was a new strategy?

JMW
www.ViscoAnalyser.com

 

RE: Question of vehicular safety

This is a mechanical engineering forum, it is refreshing to hear the "energy" thought.  

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

Quote:
"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

We can strangle the industry now or decapitate it later when the resources start to run out.

Engineering is the art of creating things you need, from things you can get.

RE: Question of vehicular safety

KACarrol,

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

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