Speedraser

I think MetalSolid's reminder of Newton's Law makes the point. If a vehicle hits a truly unyielding object, such as a concrete wall, that wall pushes back with the same force as the object that struck it -- the equal and opposite reaction. An F150 going 40 that hits a wall exerts a force on that wall, and the F150 experiences the equal and opposite reaction of that same force -- that of an F150 going 40 mph. Similarly, an F150 going 40 that hits an identical F150 head-on moving at 40 experiences the force of an F150 going 40 -- the same crash forces as the F150 that hits the wall at 40. Since the wall absorbs NO energy, ALL of the F150's energy is absorbed by that F150.

mpm '95 C4

The likelihood of two vehicles at 40 mph hitting so squarely that they wouldn't send some energy careening off in another direction is a lot slimmer then hitting a wall at 40. I'd take my chances trying to cause a glancing blow.

Many times (like Dale Earnhardt GRHS) it's not the impact itself, but it's the results of complete deceleration from hitting an immovable object - like a wall. The F150 looks like it crunched right into the wall with no rebound, and the rear mass continued to crush into the passenger compartment.

Water based organs liquify <img border="0" title="" alt="[Eek!]" src="eek.gif" /> .

MetalSolid

<img src="http://www.adn.com/ips_rich_content/57-m_hummer.jpg" alt=" - " />

Rich Sandor

And the correct answer is:

DON'T HIT ANYTHING, STUPID!

LOL

Richard C4S

The big news 2 years ago was that F-150 was fatal in a glancing head on collision. That's why I unloaded my supercab. Seems not to be the case for Expedition/Navigator though. Must have a slightly different structure. I still wouldnt want to get caught in a Mini. Jeez, can you imagine getting rear ended in a Mini by one of these behemoths?

Flying Finn

Guys,

Speedracer is right.

Obviously this is theorethical question (no angle, wall don't give up, exactly equal vechiles etc.) but both situations are the same.

Maybe hard to imagine, but think of it it, if you'd place that brick wall between those two F-150s and then both cars would hit the wall (from opposite direction!). both of cars would still hit the brick wall at 40 mph (which would remain where it is, as it would in the case where only one car hit it), right? Not 80 mph as some suggested.

NHTSA might be bogus but that's the way this 'trivia' is.

I dunno why I even asked this & now I'm explaining it here...
Sorry guys, I guess I had too much spare time, was bored or something... <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" />

PogueMoHone

Congratulations, Speedraser!

Speedraser

Well, gee, Colm, I don't know what to say <img border="0" title="" alt="[Wink]" src="wink.gif" />

Flying Finn

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by Speedraser:
<strong>Well, gee, Colm, I don't know what to say <img border="0" title="" alt="[Wink]" src="wink.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">My technology institute's physics teacher would be very proud of you! <img border="0" alt="[king]" title="" src="graemlins/r.gif" />

(If that old numbnut still teaches there! )

John Murray

OK. Same two F150's. Same speed. Same angle, but this time a train leaves Boston a 8:36am traveling at a speed of 72.6 mph, with a tailwind of 14.8 mph. What happens then?

PogueMoHone

Those on the train celebrate?

John Murray

Yes. BUT, only with 2.6 bottles of Louis Jadot, chilled of course.

Carrera GT

Huh? Short answer: for Pete's SAKE!

This article (http://www.bridger.us/2002/12/16/CrashTestingMINICooperVsFordF150) was written by someone with very little clue. The real issue is survivability and only the test data from the crash test dummies would reveal the fates of the driver in each case. Any parent who has gone through the business of getting an effective child seat for their new born or toddler will (if they're the typical Porsche owner) have gone through the self-education process to understand the issue of crash safety and survivability. This article (and this thread) demonstrate a lack of awareness of the basics.

There are so many misconceptions in this short thread, I don't know where to start. First up, the combined 80mph total is a much worse business. If you're not 100% clear on this, take a defensive driving course or read authoritative information or talk with a recognised road safety authority, don't just take a forum posting (including mine, below...)

The people talking about the 80mph incidental speed are correct -- 2x40mph is far worse than -- but not simply twice as bad as -- 1x40mph+1x0mph. Whoever quoted the NHTSA, please post a link so I can read this nonsense. I googled <a href="http://www.nhtsa.dot.gov/" target="_blank">http://www.nhtsa.dot.gov/</a> and other non-US vehicle safety sites (UK, Australia) and couldn't find any authority suggesting that "brick wall" tests simulate head-on collisions in any extrapolation, it's all "one-sided" based on the "effective incidental impact velocity subjective to a single vehicle, not simulating specific vehicle-to-vehicle scenarios."

The conservation of momentum could, theoretically be identical. In reality, once the event initiates at the incidental combined velocity, nothing will be symmetrical. Each occupant would experience deceleration forces from 40mph. Seat belts and air-bags to the rescue. But then the chassis of each car experiences an 80mph incidental collision at the point of contact which dissipates through both cars. There's two cars to create the energy at impact and two cars to absorb and dissipate the energy, but the point of origin will begin with an 80mph event, not two 40mph events.

A rule for safe driving -- it's always better to find a solid obstruction that to encounter a vehicle traveling in the opposite direction.

Enough on that; let's get to the crux of the matter, survivability. Aside from the woeful state of the broken-legged chap in the F-150 -- which weighs 4000lb, where did this 6000lb number come from? A fully laden Expedition? -- the real issue becomes the effect of the airbag, the seat belt and the duration of the event (how long did the driver's body have to slow down from 40mph to zero?) In other words, if the Mini driver had two feet to stop and the cabin is still integral, the driver's organs and brain might be mush. If the F-150 owner had four or five feet to slow down, the cabin has broken his legs, but his body has not experienced fatal deceleration trauma.

But this test was a frontal offset, which exposes the chassis weakness (loss of integrity in the cabin) and crumple zone (ability to absorb and dissipate the total forward momentum of the mass of the vehicle) and this shows that a 4000lb (not even the Expedition weighs 6000lb ... only the Range Rover gets that heavy ... I guess the Excursion is up there) truck has a lot of weight behind the cabin that just wants to keep going. Offset collisions are killers. Full frontal collisions are considerable more survivable. Sadly, cars and roads are designed to increase the likelihood of frontal offset collisions. But at least we have a painted line there to make sure nobody strays onto the wrong side of a country road at 75mph.

My final point, as mentioned by others in the thread is the reality of road collisions. A mini and an F-150 colliding in any scenario, the 2500lb car will suffer disproportionately worse than the 4000lb car. I've studied Saab and Volvo tests that show the survivability of "light" cars is all but zero when colliding with "heavy" cars because the deceleration of the heavy car transfers to the light car -- the light car literally goes in the direction of the heavy car after impact, thus the occupants of the heavy car have even more time to decelerate while the occupants of the light car have even (fatally) less time and end up traveling at some speed (even if it's only 5mph or 10mph for a split second) in a "reverse" direction causing fatal internal deceleration trauma.

If people in small cars have any reason to complain about SUVs, it's not the effect on the environment (which is, for the most part, bogus, spurious hysteria) it's the impact on road safety. I have an SUV for towing and camping etc., but we use it for commuting as a matter of "arms escalation" ... I just don't see myself sharing the road with these 6000lb+ behemoths in a 2000lb sports car -- any collision will be potentially fatal as their bumper comes over the front of my bonnet ("hood") and in through the windscreen ("windshield") so no level of crumple zone or air-bags will come to save me or my family. I'd gladly give up my individuality and drive a generic commuter vehicle if everyone did the same and we'd all be safe and find it easier to park etc. But today, that's not a foreseeable reality.

Cheers,

Speedraser

CarreraGT,
Re-read my last post (top of pg 2 in this thread). From a purely theoretical physics viewpoint, the 40 into a wall (zero angle) IS identical to two identical vehicles going 40 hitting head-on (again, zero angle). Although the closing speed is 80, both vehicles crumple rather than just one. Whether or not either "perfect" crash happens in the real world was not the point. And no one here said he would choose to be in the Mini if it and the F-150 hit each other.

Also, the dummies in the crash-test vehicles are instrumented -- the deceleration at various parts of their "bodies" is measured. The Mini did better than the F-150 in the offset test because the dummies recorded lower deceleration figures, not just because the passenger compartment didn't squash them. The Mini is the better seat to have IF you have the crash that was tested -- offset into an immovable barrier.

I hesitate to say this given your "arms-escalation" commuter-vehicle thinking, but it is NOT always better to hit a solid object. If you hit something softer and/or lighter than your own vehicle, you may well be better off than if you hit a wall. If you were in the F-150, would you rather hit a wall or a Mini? The Mini's occupants' will hope you don't think of this at the critical moment.

It is very interesting that SUVs don't have better safety records. The 993 has a better injury record than virtually all SUVs. See this site for crash injury records: shttp://www.hwysafety.org/vehicle_ratings/ictl/previous/ictl_0399.pdf.
Much of this must have to do with active safety -- the ability to avoid an accident. I wouldn't want to hit an SUV in any 911, but I'm less likely to crash in the first place. Look at emergency lane change abilities, stopping distances, etc. Most Porsches can stop from 70 in 160-170 feet. Most SUVs require over 200. Most Porsches can stop from 80 in 210-220 feet; most SUVs need over 250 feet, and some require over 300. Think about that: the Porsche driver could have stopped completely, while the SUV is still moving at considerable speed for another 50 - 80 feet. It could mean the difference between not having a crash, or hitting something at 30-40 mph or more. I'll take not having the crash (I just hope an SUV isn't behind me if I need the Porsche's brakes). Of course, some crashes are unavoidable, but most are. Needless to say, far more SUVs roll over than cars, whether the driver simply makes a mistake, or he tries unsuccessfully to avoid an accident that a car could have avoided successfully.

Carrera GT

I was trying my hand at sarcasm with the comments about arms escalation -- and apparently I didn't convey much wit.

My father taught physics -- that's not to say that I learned physics, but he tried to teach.

This thread reminded me of just how difficult it is to think clearly in terms of inertia, momentum and elastic and ineslatic collisions. There's no point going deeper into the physics of how car collisions are not as simple as science room experiments of inelastic collisions.

And I won't insult the forum with a tour of Newton's laws of motion ... anyone with a browser and the ability to type in Google can purport to be a genius in almost any topic on a forum.

As my Dad is fond of saying, especially whenever he hears of my latest car:

"It's not the speed that kills you ...
it's the stopping."

Alright. One question:

Using the example of two cars colliding together without involving any other object and each car having one occupant -- regardless of the relative speed or mass of each vehicle or the incidental angle of collision or relative direction of motion -- how many discrete collisions occur before all major objects come to rest and which collision chain of events contributes most significantly to survivability for the two drivers?

I hope others are finding this thread entertaining -- it's an old horey chestnut of crash safety and entirely relevant to any Porsche enthusiast on their next track day just as it's important to first time SUV owners that might not have taken pause to consider their new mode of transport.

By the way, that link to <a href="http://www.hwysafety.org" target="_blank">www.hwysafety.org</a> sends me to their home page -- I've tried removing bits of the URL, but couldn't get anything on 993 or Porsche safety.

I did find this about men versus women
<a href="http://www.google.com/url?sa=U&start=1&q=http://www.hwysafety.org/safety_facts/fatality_facts/gender.pdf&e=747" target="_blank">http://www.google.com/url?sa=U&start=1&q=http://www.hwysafety.org/safety_facts/fatality_facts/gender.pdf&e=747</a>

Which ratherly dryly states:
"
More men than women die each year in motor vehicle
crashes. Men typically drive more miles than women and
engage more often in risky driving practices including not
using a safety belt, driving while impaired by alcohol, and
speeding.
However, deaths of female drivers have increased during
the past 20 years while male driver deaths have declined.
More women now are licensed than in the past. They drive
more miles and are more likely to be driving at night. The
fatal crash rate per 100 million miles of travel for male
and female drivers decreased similarly between 1977 and
1995 ? a 45 percent decrease for female drivers and a
41 percent decrease for male drivers.1
"

Now, to me, I think they're saying that men are better drivers than women ...