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Please just remember to be careful! watch

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    (Original post by ciderpeter)
    Seeing things like that makes you think about speed etc and whether it is worth risking your life and the people in other cars life to just go a little bit faster, in my car especially (escort), it is built to go fast, but it is not built to stop fast and it is not built to be safe either.
    This is where being a pessimist comes in handy - you're constantly assuming the worst therefore will tend to err on the safe side. The problem is you become so aware of the high possibility of being killed if say, you did something as simple as moved a few iches to the left, you freak out. You need the balance between being sufficiently scared so you don't risk other people's lives, and having enough confidence to drive well in the first place.

    I wish track days were more popular (so I guess cheaper?) - people could really get that aggressive driving out of their systems and be more chilled on the road.
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    (Original post by pghstochaj)
    I think it's more than possible, a quick search shows it could be anything from 40 G to 100 G.

    According to wikipedia (so don't take it as fact!!!):

    Involuntarily: Formula One race car driver David Purley survived an estimated 179.8 g in 1977 when he decelerated from 107 mph (172 km/h) to 0 in a distance of 26 inches (66 cm) after his throttle got stuck wide open and he hit a wall.
    Well, if you say so...

    I just find it surprising, considering that fighter planes "only" reach about 9g. And thats cornering at quite significantly above 100mph. So for braking forces from 30mph to be able to reach 60g is interesting.

    I suppose a 60g force is possible when braking from 30mph. But (by my reckoning), you'd have to stop in 0.00226 seconds and 0.00150 metres. So actually it's more likely *possible* in a crash, but only if the car took none of the force by crumpling, forcing you to take the deceleration. As cars (and the things they crash into) rather considerately deform, then I'd guess 60g doesnt actually happen.

    Thats rather a big tangent, however
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    It's an entirely irrelevant point if a fighter plane can pull a max of x g, i assure you that if you flew that plane into a brick wall and it would be an entirely different matter

    However, I doubt when we quote g-forces you're talking overall, more about individual body parts.

    Rather than me writing anything or doing calculations, take a look at:

    http://hypertextbook.com/physics/mec.../acceleration/

    Also:

    http://www.becomehealthynow.com/arti...oresearch/615/

    Typically, although other factors are involved, I was under the impression that it takes over 40g to set off an airbag. I may well be wrong.
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    There are three phases to a car crash.

    Phase 1: The initial impact, the car stops and you fly forward hopefully stopped by the seatbelt.

    Phase 2: Your body stops but your neck continues until the end of its reach and then flies back, pulling your neck muscles (whiplash)

    Phase 3: Although your body and neck have now stopped, your internal organs are still moving, they smash into your rib cage stopping instantly. This is the most crucial phase, depending on how fast your internal organs hit your rib cage dictates whether you live or die.

    The above all happens in milliseconds, but the effects can be lifelong. Until you have been in a crash, you don't appreciate the forces involved. Crumple zones do bugger all, they just absorb the energy, the energy is still transfered to you. I crashed at like 20mph, i still had whiplash and the biggest, badest bruise on my shoulder from the seatbelt. There are some big forces involved from stopping suddenly!

    Graham
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    (Original post by gbduo)
    ...The above all happens in milliseconds, but the effects can be lifelong. Until you have been in a crash, you don't appreciate the forces involved. Crumple zones do bugger all, they just absorb the energy, the energy is still transfered to you. I crashed at like 20mph, i still had whiplash and the biggest, badest bruise on my shoulder from the seatbelt. There are some big forces involved from stopping suddenly!...
    Yes, I'll grant that. But the car doesnt stop *instantaneously*, which is what would need to happen for *you* to take a 60g decelerative force. It absorbs a lot of the force by bending the metal of the car (and remember that whatever you hit will take a fair amount of the force too). You will take much longer than two hundredths of a second to stop!

    I know there are big forces involved in stopping suddenly, but the force you're quoting is sixty times the gravitiational pull of the earth.

    By the way pghstochaj, one of the links you posted says that:
    The acceleration during the crash that killed Diana, Princess of Wales, in 1997 was estimated to have been on the order of 70 to 100 g, which was intense enough to tear the pulmonary artery from her heart -- an injury that is nearly impossible to survive. Had she been wearing a seat belt, the acceleration would have been something more like 30 or 35 g -- enough to break a rib or two, but not nearly enough to kill most people.
    That's what I've been saying - Yes, there are huge forces involved, but the majority of them are absorbed by the car, seatbelt, and airbag (if its there). Also remember that the crash that article references occurred at *much* more than 30mph.
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    All we are talking is G-force is it not? 'G-force' is not a force, it just has that name. It is irrelevant how much of a crumple zone of a car, it's how long it slows the crash is it not?

    Acceleration or retardation = dv/dt
    So, for example, at 15 m/s if the initial impact from 15-0 m/s takes 0.1 seconds, that's a retardation of 150 m/s/s, so without getting a calculator, about 15 g.

    However, retardation is by no means uniform. It may be that the initial retardation from 15 m/s is 100g (if you have a tough initial outer shell) but on average it may be that 15 g from above.

    In terms of 'g-force', the only thing you can change is the time the crash takes, of course you can look at the crumple zones in another number of ways such as the energy removed.

    I don't do any of this type of maths anymore so I may well be wrong.

    What do I know anyway I am just a chemical engineering student...
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    I'm going to the do the calculations on this soon, it was bugging me last night so much I almost took my calculator into bed with me. :eek:
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    (Original post by pghstochaj)
    ...In terms of 'g-force', the only thing you can change is the time the crash takes, of course you can look at the crumple zones in another number of ways such as the energy removed....
    Exactly. I think we're getting confused as to *where* the deceleration is...

    Certainly in a crash, parts of the car will have massive decelerative forces, because they stop almost instananeously (in, say, a crash straight into a brick wall). But the crumpling of the car means that the passenger cell will decelerate slower than, say, the front of the car that hits the wall. Also, the occupants are (usually) wearing seat belts, which also slow you down a bit slower. If there are airbags, they also help.

    So whilst there *are* massive decelerations involved for *parts* of the car, for the passenger there are *lesser* decelerations. They're still rather large, but at the speeds we're on about (30mph), not usually enough to kill you.

    I do get the feeling this has gone on longer than it should have, though
 
 
 
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