I'm in the hospital after car accident. Questions about G's

Hello Everyone,

I’m sitting in a hospital bed typing this on my phone. Last night I was in a pretty bad single car accident. I can only surmise that I possibly drifted off for a few secinds behind the wheel. My car left the road onto a very vey large shoulder. That’s when i guess I came too.

The grass was wet and neither t the brakes nor the steering did much of anything.Apparently i jumped a driveway and went airborne about 30’, then hit lets say a 40’ tall pine tree head on.

I’m very bruised, especially where the seat belt and air bag hit me. I already have an injured back and it came out worst of all, I can barely move without screaming in pain. Although after seeing pictures of the car, I know that I’m very lucky to even be alive.

I can’t say the exact speed that I hit the tree but I do know that I was going about 60 miles an hour on the road prior to leaving it. If I had to guess because I was well aware of the impact I guess I was traveling between 50 and 55 miles an hour when I hit the tree. I was driving a 2009 CX-9, which is a fairly big vehicle. It’s kind of funny because when the impact happen I’m more heard it than I felt it and then I was out of it for a little bit .

I was wondering if any of you math types could take a guess of how many G’s my body experience when it hit the tree? Maybe with the information I’ve given it’s not possible to determine that but I just thought it’d be interesting to know. Thanks in advance and I’m happy that I’m still around to be able to talk.

Glad you lived through it and are coherent enough to tell the tale!

The only G-force info I could find was related to acceleration, not sudden stops.

If any of your read that, I edited it. Sorry for the mistakes. I’m a but doozy.

Man, I don’t know how hard you hit, but don’t do it again.:eek: Seriously, glad you’re ok. Modern cars are the shit when it comes to hitting stuff and living to tell the tale.

Here’s a handy calculator from GSU. Note it gives force instead of gs, but just use 1 lb for mass and read the lb output as gs.

Speed is your guess. The big question is stopping distance. Basically, how far in the did the front of the car crumple? Seatbelts also play a role in stretching so that’s something the calculator lets you play with.

I’m guessing something in the 50-80 gs range under ideal Physics. But a lot lower in real life. A survivable range for a split second.

I can say without a doubt that the cars design team saved my life. I haven’t seen it yet since the accident, but my wife brought me lots of pictures. The front end crumbles and you can easily follow the energy trail as more and more parts for destroyed. She said you can see the ground through the drivers floor.

When all was said and done there was barely enough space for my body in the seat. I couldn’t open the driver for so had to crawl over the center console and out the passengers side.

I saw smoke and thought the car was on fire (it wasn’t) so it’s amazing how fast you can move while injured if you think you’re about to become crispy! I got maybe to the back bumper before the pain kicked in.

I have zero doubt had I’d been driving a smaller car or not wearing my seatbelt, I’d be dead.

That is total nonsense. Back in ye olden days, cars were solid, with steel chassis and it took a fair old whack to even bend a bumper. This meant that when they impacted a tree at speed a great deal of the energy involved was transferred to the occupants with catastrophic consequences.

Modern cars are designed to crumple and in doing so much of the energy is absorbed. Add in airbags and seat belts and the occupants have a considerably greater chance of survival and survival without life-changing injury.

Are you saying you’re ass sleep? :smiley:

Pretty sure that he meant “the shit” as a positive. Might be specific to the US.

@bob++. I believe that in the phrase “the shit”, the “the” essentially functions as a “not”. English is the easy…

obbn, although I don’t have an answer to your factual question about Gs, I’d like to offer my congratulations on not being dead. Have you also been considering the important scientific question about what sort of factors might have been involved in your nodding off briefly, and how to stop them happening again?

Impact metrics are generally stated in terms of peak acceleration levels–often stated as “g” (equivalent surface gravity of the Earth) = 9.81 m/s[SUP]2[/SUP] = 32.2 ft/s[SUP]2[/SUP] not “G” which is the acceleration constant–because acceleration is directly measurable and it is easy to calculate an equivalent inertial load, but it is actually the rapid change in acceleration (jerk in physics terms) which gives the actual impulse (force divided by time). A very rapid change in increase in acceleration will do more damage than a slower application both by dint of giving the body less time to respond and because the application of impulse will be localized to the first points of contact, hence why in a frontal impact the outline of the seatbelt can often be seen with distinct abrasions where the edges of the belt cut into the body.

Neither human or car bodies are rigid objects under heavy impact so in terms of damage the orientation of body with respect to the acceleration, how much of the impulse is absorbed or dampened by deformation, and how the body is restrained will dictate the experienced acceleration and what kind and how much damage will occur. A body can tolerate levels of a few hundred g of acceleration for brief periods, and accelerations in the tens of g for a few seconds. The Snell Foundation “2015 Standard For Protective Headgear For Use with Motorcycles and Other Motorized Vehicles” defines a maximum allowable peak acceleration of 275 g for an impact speed of 7.75 m/s as measured inside the helmet, which is supposed to prevent brain damage (concussion) for a frontal impact although the potential for damage has as much to do with the direction of impact as the experienced acceleration.

So for the o.p., I don’t think there is a simple answer to your question. A rough guess for frontal impact at 60 mph in a modern automobile with an approximate 0.5 m effective crush zone is that the peak acceleration as experienced at the driver’s seat is on close order of 80 g, but experienced peak acceleration will be reduced by both the airbag, stretch in the seatbelt, and any other occupant safety mechanisms, e.g. anti-whiplash devices. If your head or other body part impacted a solid surface, that would increase to hundreds or thousands of g and cause blunt or penetrating trauma, hence why modern occupant safety measures have reduced severe injury and death in moderate speed accidents, and have allowed survival in high speed accidents in which occupants would have otherwise exited the vehicle in an uncontrolled manner at a high rate of speed and be found a significant distance away from the impact site.

Stranger

Airbags can produce a pretty good cloud of crap inside the car. It’s really disorienting and can lead to the fear of a fire.

Here’s a crash test of the 2008 CX-9. Stepping through frames, counting from when the bumper first touches the barrier, the driver’s head moves about 50 inches before stopping. (I’m pretty sure the yellow/black stripes are 1 inch apart.) About half of that is the crumple zone crumpling, the rest is the seat belt stretching/slipping (also a safety feature) and the head moving forward.

Decelerating from 60 mph to 0 over 50 inch distance is an average deceleration of 29 G.

Of course the peak would be much higher. I wouldn’t be surprised if it was double that.

I can give you an approximate mathematical solution to your question, but it’s only valid for spherical chickens in a vacuum.

Just kidding. Glad you survived!

Wow, I’m glad you’re still able to post after that.

Modern car onboard computers will log all sorts of data about the vehicle speed, brake pedal position, throttle position, etc. for some time leading up to the event. Maybe even the peak G from the various accelerometers. It might be neat / super morbid to get a look at that data. Your insurance company might even do it routinely.

Holy smokes, that sounds terribly frightening. Glad you survived. I hope you find relief for the pain you are in. Heal well and soon.

“Modern cars are shit” = bad.

“Modern cars are THE shit” = good.

They hurt like hell, too. But it WAY better than hitting a steering wheel or windshield.
OP, your are truly lucky. Send your wife out for lottery tickets. Good luck.

“The worst part was hitting the ground
Not the feeling so much as the sound
Can’t help but wonder if all this is real 'cause
Tonight is the night I fell asleep at the wheel.”
–Barenaked Ladies

Stranger, you might want to double-check that. Impulse (change in momentum) is force times time, not divided. Jerk is only relevant to the extent that you can brace yourself for acceleration.