G-Force

[blitz2]

Hey,

I was talking to my friend earlier about car crashes. He told me during a car crash, a person experiences a force of 100G's when hitting a wall at 100km/h. We got into an argument about this because from what i know, rockets produce around 30G's. I don't see how someone can live through being hit by 100G's. Can some one please clear this up for me?

Thanks

[Buffy]

Remember G-Force is a measure of *acceleration* not *speed*.

A rocket accelerates very rapidly, but its *nothing* compared to the deceleration of going from 100 kph to 0 in a tenth of a second!

Drive safe,
Buffy

[blitz2]

Thanks for the quick reply. I understand the acceleration part. But how would someone survive a collision of 100G's during a car crash?

[Buffy]

Originally Posted by blitz2

But how would someone survive a collision of 100G's during a car crash?

Unfortunately, they wouldn't. Dale Earnhardt found that out the hard way...

Travel too fast and you miss all you are traveling for,
Buffy

[freeztar]

Originally Posted by Buffy

Travel too fast and you miss all you are traveling for,

Or maybe not??

“I'm thinking, ‘I've got to get this parachute that's still attached to me off,’ ” Holmes said. “[The reserve's] either going to make things worse, or there's a very slight chance it's going to make it better.”

Holmes cut away the main chute, and pulled the cord for the reserve chute. When that didn't work, there was nothing left for Holmes to do but think of something to say into the helmet camera. “I thought, ‘Oh, I've got a camera on my head. Say something,’ ” Holmes recalled.

In hindsight, Holmes realizes that “I'm dead. Bye” didn't really cover everything the British citizen wanted to say to his family and friends...

He suffered a collapsed lung and broken ankle that may require further surgery, but plans to jump again. He called the incident a “freak accident” that has changed the way he looks it life.

“I will certainly jump. It's what I do. I love it,” Holmes said.

Man lands without chute after falling two miles @ 9.8m/s^2 - (minus local atmosphere and wind conditions)

"Freak accident"
But sure, I'll jump again!

Here is a site that seems somewhat credible and has some good info on acceleration and subsequent human death.
Acceleration That Would Kill a Human

The devastating car crash of Princess Diana of Wales in 1997 was estimated to range somewhere between 70 - 100 g's. This accident was intense enough to pull the pulmonary artery from her heart. It's important to understand that velocity alone plays no role in the symptoms of injuries of a human.

[CraigD]

It’s important to understand that acceleration depends a lot on what body is being measured, and over what time period. A small mass experiencing a very large acceleration for a very short time involved very little energy – although I’ve not read or derived detailed calculations, I’ve encountered estimates of the acceleration experienced by the contact sections of your skin during actions as harmless as hand-clapping as high as several hundred g. The electronic recorders in race cars have registered momentary g-forces during crashes around 75 g, while the highest acceleration ever survived by a human being is estimated to be 178 g (David Purley, in 1977).

So, while a good rule of thumb for human lethality is 100 g – this is roughly the acceleration necessary to damage important arteries, capillaries, and veins that supply blood to the brain – a very short duration acceleration many times higher may not even cause noticeable injury, while a acceleration of only 2 g or so, sustained for many days, will cause fatal accumulation of fluid in the lungs.

For an acceleration to be dangerous to structure like a human body, it must last long enough to accelerate some fragile part of the body to a velocity high enough to damage it when it finally “runs out of slack” and stops moving. The part of the body moving, and the direction it moves, is important – a fairly small velocity of ones head, if not arrested by a headrest or similar device, can cause serious or even fatal damage to the arteries and veins in the neck, or the spine. If the motion of ones head is stopped by the wrong sort of object, at the wrong angle, a small acceleration can be instantly fatal. Famous race car driver Dale Earnhardt died instantly from a relatively low-speed impact of his face with his steering wheel that resulted in a basilar skull fracture.

In short, the mechanics of the human body under various force and acceleration is complicated, as is the measurement of very brief acceleration, making an exact correlation of the two difficult. “100 g is fatal” is a reasonable rule of thumb, but only a rule of thumb. A given instrument registering, or a given calculation indicating 100 g momentary acceleration may not be a good indication of an event being fatal to a human, while a low reading is no guarantee that an event will not be.

There are many web resources exploring the subject in greater detail, including a decent summary at the wikipedia article “g-force”.

[Buffy]

Originally Posted by CraigD

Famous race car driver Dale Earnhardt died instantly from a relatively low-speed impact of his face with his steering wheel that resulted in a basilar skull fracture.

Just a note that 150 miles per hour--the estimated speed that he hit the wall after decelerating from over 200 mph due to being pushed sideways--is not really "low-speed." Watching this live was one of the low-lights of my life....

The winner ain't the one with the fastest car its the one who refuses to lose,

[CraigD]

Originally Posted by Buffy

Watching this live was one of the low-lights of my life...

My reaction at the time was first confusion – the TV announcers mistakenly identified Ken Schrader leaning into Dale Earnhardt’s car as Dale getting out of it, so, along with the announcers and most of the viewers, I believed everybody was OK. When they medivaced him, I assumed some sort of non-life threatening injury, when in fact he was already heart and brain dead. When they announced first a serious injury, then that Dale was dead, I was shocked – I simply couldn’t square my faith in NASCAR safety engineering, the minor-looking replays of the crash, and the visible evidence that the car had done exactly what it was designed to do, absorbing energy by crumpling its front end, with the news that the crash had killed him instantly.

Dale was never my favorite driver, either for his style, personality, or skills, but his death hit me emotionally. Even my wife, who’s usual reaction to racing accidents is something along the line of “those aggressive adventure junkies deserve whatever they get”, who thought at the time that Dale Earnhardt and Richard Petty, and possibly Burt Renolds were the same person (not a close follower of NASCAR, or observant about hats, my wife), and who considers Grand Theft Auto and NASCAR to be approximately the same “sport”, was shaken.

Seeing nearly ever driver of racecars of all sorts walking around in HANS devices somehow makes me feel better about the whole business, and reaffirms my faith in technology and good sense. It also nearly always brings Dale to mind – had he been wearing one, it’s almost certain he’d have survived, and likely walked away from the crash that killed him. The device is a great example of the application of the science of biomechanical engineering to the issues we’ve been discussing in this thread.