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Old 1st November 2012, 21:38   #31
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Default Re: Understanding Seat Belts : Layman Language

Quote:
Originally Posted by torquecurve View Post
But I think you are digressing from the whole point. I am just trying to make people aware that wearing a seatbelt does really help.
Digressing? Don't really think so.

Seatbelts are important. Seatbelts save lives. Well known. Really does not have to be repeated.
So it is unusual when a whole post is devoted to that. Let alone a whole new thread.
So when a new thread is started, one would expect that the lead post would be well researched, illuminating, authoritative. The definitive article. And subsequent posts building on that.
So when those posts have erroneous information, and dubious 'facts and figures', it takes away from the seriousness of the message, and lowers the quality of the board. The most glaring is the one on basic calculations, and the conclusions drawn for braking.

Let me amplify.

Quote:
S=D/t so Delta S=DeltaD/ Delta t
hence, Delta D = Delta S * Delta T.

In this case however the Delta T is considered to be about 1 second and so didnt make a difference to my further calculation.
After calculating (twice!), you get that stopping distance when evenly decelarating from 60 Km/ hr to 0 Km/ hr in 1 sec will take 16.7 m.
It will not. It will take 8.3 m.

Quote:
I dont know why does that sound convulted to you.
We need to calculate acceleration values. Bringing in mass and force, and then eliminating it definitely seems convoluted to me. In any case, the figure (1.7 g) was right.

Quote:
You can look up some websites and I am sure you will find calculations such as these. Otherwise, you can use the OpenSource Math software.
I hope not to come upon sites which calculate g figures the way you have done!
And I'll rather stick to some (very very basic) textbooks. And for this pen and paper will more than suffice.

Quote:
Cars on dry tarmac with all discs maybe provide this stopping power.
This is what I find most surprising: the lack of feel. For numbers. For the subject.
A vehicle stopping from 60 Km/ hr in 1 sec, 8.33 (or 16.7 m) at 1.7 g seems OK? Do check out the braking performance figures of cars. In fact, make that hypercars. And then think about why.

Quote:
In case of a crash you would slow down in less than 0.1 of a second in less than 1-2 metres probably.
We were discussing braking (As initially brought up by you), not crashes.

Quote:
The G force is equivalent to a distance travelled by a person. I was just trying to make my point.
Still don't get what point you are trying to make. Could you please amplify. In a free fall, the only force acting is that of gravity. And from the falling bodies point of view, he is weightless.

Regards
Sutripta
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Old 2nd November 2012, 09:12   #32
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Default Re: Understanding Seat Belts : Layman Language

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Originally Posted by rohanjf View Post
Can ABS reduce the injuries that are caused by seatbelts (dislocated shoulder, fractured ribs etc)?

I feel so, because these injuries are caused by rapid deceleration. However, when ABS gets activated, the deceleration rate is not constant. In fact, it keeps reaching 0. Can the body adjust to the ABS rhythm, and thus, reduce the damage to itself?
I do not think ABS reduces injuries that are caused by seatbelts though I may be wrong. What ABS does is it avoids locking up of wheels and keeps them rolling so that the driver can still provide steering input.


I feel ABS is one of the most misunderstood features among laymen. I have actually heard people trying to convince others that ABS is just to prevent the car from toppling over while cornering at high speeds, and is not needed if we are on straight highways.


Quote:
Originally Posted by Sutripta View Post
After calculating (twice!), you get that stopping distance when evenly decelarating from 60 Km/ hr to 0 Km/ hr in 1 sec will take 16.7 m.
It will not. It will take 8.3 m.
Sutripta is correct. dv/dt is the decelartion of the vehicle and 16.67m.s2 is the deceleration of the vehicle and not the distance to stop.
deceleration calculated by v = u + at .
8.3m is the correct distance calculated by the formula S = ut + 0.5 at2.

My 2cents for people who dismiss seat belts/helmets is "If you bought a mask when you heard some people died of swine flu, you better belt up as many more have died due to not wearing seat belts/helmets"
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Old 2nd November 2012, 09:35   #33
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Default Re: Understanding Seat Belts : Layman Language

Quote:
Originally Posted by rohanjf View Post
Can ABS reduce the injuries that are caused by seatbelts (dislocated shoulder, fractured ribs etc)?

I feel so, because these injuries are caused by rapid deceleration. However, when ABS gets activated, the deceleration rate is not constant. In fact, it keeps reaching 0. Can the body adjust to the ABS rhythm, and thus, reduce the damage to itself?
Will Airbags not prevent this by providing an instantaneous cushion? I believe the airbags help in pinning the individual in place, thereby reducing whiplash and thus also preventing the said injuries as stated by you.

It remains that seatbelts are sadly and extremely ignored in our Bharatvarsh, along-with rules around seating of children in a vehicle.
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Old 2nd November 2012, 09:41   #34
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Default Re: Understanding Seat Belts : Layman Language

Thanks for the explanation Sir,

I do use seat belts and insist on the driver side passenger using them for two reasons:A)Safety, B)Rule violation, penalties.

Thanks to your article, and the seriousness of the consequences of not using the belt have made me decide that from now on I will insist my rear passengers also use the belts. Else they wont travel in my car.

Once again thanks for simplifying the science behind the seat belts.
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Old 3rd November 2012, 11:28   #35
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Default Re: Understanding Seat Belts : Layman Language

This has been an eye opener for me ! I have started wearing seatbelts even in city driving from last 1 year or so after having met with a disaster so near to my home. We tend to think there is no need to wear seatbelt in City as speed is less.

Another improtant aspect is ensuring your co-passengers are wearing them too. I will ask them to get down if they dont want to wear seat belts from now on.

Huge thanks for starting this thread.
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Old 3rd November 2012, 18:58   #36
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Quote:
Originally Posted by Sutripta
Digressing? Don't really think so.

Seatbelts are important. Seatbelts save lives. Well known. Really does not have to be repeated.
So it is unusual when a whole post is devoted to that. Let alone a whole new thread.
So when a new thread is started, one would expect that the lead post would be well researched, illuminating, authoritative. The definitive article. And subsequent posts building on that.
So when those posts have erroneous information, and dubious 'facts and figures', it takes away from the seriousness of the message, and lowers the quality of the board. The most glaring is the one on basic calculations, and the conclusions drawn for braking.

Let me amplify.

After calculating (twice!), you get that stopping distance when evenly decelarating from 60 Km/ hr to 0 Km/ hr in 1 sec will take 16.7 m.
It will not. It will take 8.3 m.

We need to calculate acceleration values. Bringing in mass and force, and then eliminating it definitely seems convoluted to me. In any case, the figure (1.7 g) was right.

I hope not to come upon sites which calculate g figures the way you have done!
And I'll rather stick to some (very very basic) textbooks. And for this pen and paper will more than suffice.

This is what I find most surprising: the lack of feel. For numbers. For the subject.
A vehicle stopping from 60 Km/ hr in 1 sec, 8.33 (or 16.7 m) at 1.7 g seems OK? Do check out the braking performance figures of cars. In fact, make that hypercars. And then think about why.

We were discussing braking (As initially brought up by you), not crashes.

Still don't get what point you are trying to make. Could you please amplify. In a free fall, the only force acting is that of gravity. And from the falling bodies point of view, he is weightless.

Regards
Sutripta
I agree to what you say. I should have put some more research into this. My first thread so you could write it up to newbie mistakes please.

The reason I thought it deserved a thread by itself was because on this very forum I have seen people writing that they don't wear seatbelts as it is useless at city speeds. I even read a post where a member had written that as he can use the steering wheel to support himself he doesn't need a seatbelt.

I am enlightened however now and my next thread will be better.

Thanks and apologies.
Nik
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Old 3rd November 2012, 20:20   #37
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Default Re: Understanding Seat Belts : Layman Language

Quote:
Originally Posted by torquecurve View Post
The reason I thought it deserved a thread by itself was because on this very forum I have seen people writing that they don't wear seatbelts as it is useless at city speeds. I even read a post where a member had written that as he can use the steering wheel to support himself he doesn't need a seatbelt.
Thanks for starting this excellent thread. Whether the mathematics is correct or not, the thread is very relevant, and has produced some interesting discussions/viewpoints. Infact there was some heavy discussions in the ‘Bad drivers thread’ which probably have prompted you to start this one.

Just read the post right above yours to see the positive impact

Thanks again!

Last edited by vb-san : 3rd November 2012 at 20:21. Reason: spelling
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Old 4th November 2012, 21:08   #38
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Default Re: Understanding Seat Belts : Layman Language

Quote:
Originally Posted by torquecurve View Post
I should have put some more research into this.
......
I am enlightened however now and my next thread will be better.
Instead of another thread, why not put up an authoritative post on this thread only. That would be helpful and appreciated.

Regards
Sutripta
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Old 5th November 2012, 10:13   #39
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Default Re: Understanding Seat Belts : Layman Language

To me, wearing a seatbelt continues as habit even before the rules were enforced. I was taught to drive a car with seatbelts on. Just wanted to add my humble 2 cents to this wonderful thread. Seatbelts with pre-tensioners and load limiters should always be preferred. In the event of a crash, the pre-tensioner tightens the seat belt almost instantaneously to prevent the occupant from jerking forward where as a load limiter absorbs and softens the load as the passenger moves forward because of inertia. It is also helpful in case the pre-tensioner tightens the belt too much.

Last edited by Sabareesh : 5th November 2012 at 10:15.
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Old 5th November 2012, 16:07   #40
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Default Re: Understanding Seat Belts : Layman Language

May I take the privilege to add my few cents here?

1) Seat belts for ALL PASSENGERS - The driver and all passengers must wear seat belts at all times. Yes even the rear seat passengers must wear seat belts else they (especially the one in the middle) may get thrown out through the front windshield or loose a few of your precious tooth or a limb or two or can even die from the impact with the back of the front seat or the door panels or the gear lever. One cannot say which direction you may get thrown in case of an impact and which part of the car's inside you end up hitting.

2) Neck Restraints in all seats saves you from Whiplash effect - In case of a sudden frontal impact the seat belt will stop your body from hitting the dash or steering, but it does not stop here. Your body and head bounces backwards once the forward motion is stopped and your head hits back the neck restraint. Without the neck restraint in place you will have severe (fatal or permanently damaging in most cases) neck injury. Thus always keep the neck restraint in place properly adjusted for height. Please read the car manual for detailed instruction, but a general guideline the top of the neck restraint must not be lower than the top of your ear.

3) Airbag and seat belt - In cars fitted with airbags, it is even more important to wear seat belts. Otherwise the exploding airbag will most likely injure you more than the crash itself.

4) Child seat - Babies and children travelling in a car must be secured into child seats (of proper shape and size depending on the child). Incidentally most child seats for smaller children has 5 point seat belts instead of 3 point. However strong the mother's lap is, she will not be able to hold the baby back in case of a head-on collision even if she is wearing seat belts.

5) No children in front seats - One must not allow small children to seat in the front seats with or without child seats. In most developed countries, children up to a certain weight and height are not legally allowed to seat in the front seat. I vaguely remember seeing figures like 35 Kg/ 130 cms somewhere. A healthy 12 year old in the Indian context can be used as the benchmark.

These points came into my mind as I read through this thread and thought sharing them would add to my minuscule contribution towards saving a few lives.

Cheers!
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Old 5th November 2012, 17:31   #41
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Default Re: Understanding Seat Belts : Layman Language

Quote:
Originally Posted by latentpotential View Post
Will Airbags not prevent this by providing an instantaneous cushion?
NO! Please see Noopster's link which talks about some numbers regarding the explosion velocity of the airbag opening system.

Quote:
I believe the airbags help in pinning the individual in place, thereby reducing whiplash and thus also preventing the said injuries as stated by you.
I guess you are confused between airbags and seatbelts. Seat belts pin down a person who is belted. Airbag just reduces facial and ribcage injuries hence called SRS Airbag = "Secondary Restrain System", means airbags will help only with a primary restrain system = seat belts!

Quote:
It remains that seatbelts are sadly and extremely ignored in our Bharatvarsh, along-with rules around seating of children in a vehicle.
Very true! Rightly said about child seats too!
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Old 5th November 2012, 20:18   #42
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Default Re: Understanding Seat Belts : Layman Language

Seating configuration plays a very important role in seat belt effectiveness.
Too many SUVs in India have side facing seats, in the name of more seating capacity. And to the best of my knowledge, such seats do not come with seat belts. Side facing occupants, without seat belts are not only a hazard to themselves, but also to the occupants in the front seats. In case of a head on or offset collision, they would be flying forward, into the front seat occupants.
The most disturbing is when you see a lady packed into the back of such an SUV, sitting sideways, while balancing a baby in her hands and the vehicle is speeding way beyond it's safe breaking and stopping capacity. At such times all rationality deserts my mind and I simply send out a silent prayer.
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Old 5th November 2012, 21:21   #43
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Default Re: Understanding Seat Belts : Layman Language

Quote:
Originally Posted by torquecurve View Post
For people who say, "when my time comes even a seatbelt will not save me". Just one thing, don't tempt fate please.
========
The only exceptions are if you are Superman or have been given vardaan to live 100 lives. In which case, why are you using a car
OMG! I have a chevy caprice 1979 and by looking at the body work of that car, i thought it will never crumple like this one did. I thought these old cars were the safest cars on road. Seriously, my dad drives it daily and I got so terrified that I called and asked him to view this video. he says he might stop driving this car on highways now.
Thanks of lot for sharing!!!
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Old 6th November 2012, 16:11   #44
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Default Re: Understanding Seat Belts : Layman Language

Guys I have a question by which I dont mean to undermine the importance of wearing seat belts at all. I wear them in the back seat too!

Isnt the math missing something (not in case of an accident)? I mean there has to be something that prevents people from feeling that much stress (like falling from a building etc). Could it be anticipation or the fact that the force is still distributed to the entire body.
This only comes to mind since the bikers dont have seatbelts and they do just fine under hard braking.
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Old 7th November 2012, 11:18   #45
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Unhappy Re: Understanding Seat Belts : Layman Language

I don't have all the data with me but let try to explain.
Lets take an extreme case of an ariel atom.

0-160-0 data shows 10 secs approx, 0-160 for atom 6.86 secs
160-0 3.8 secs (times taken from the atom wiki)

Assumptions:
Ariel atom from 160 kmph takes about 3.8 secs to stop.

speed initial = 44.44 m/s (u)
time = 3.8
speed final =0 m/s
acceleration = accel= (speed final - speed initial)/ time
= -11.69 m/s^2 (where the minus shows direction which is backwards)

this acceleration is also experienced by you sitting in the car

assuming you weigh 80 kg the force acting on your hands

f= mass * accel
f= 80 * 11.69 = 935 N = 95 kg weight.

This shows that your wrists might not break.

What can happen is you banging your head into the steering as to prevent that your arms need to be able to do a push up with extra 15 kgs and hold it for 3.8 secs.



What happens in the case of an accident is very different.

The maximum g that a typical human can survive is about 17 g (sustained) without his/her internal organs being crushed to a pulp. (shock g 's can be a lot higher and mainly depends on the frequency of the shockwave )

assumptions

speed 100 kmph = 27.77 m/s

distance to stop = 2 m (which is typically the crush zone in the front of the car)

formulae:

initialspeed^2 - finalspeed^2 = 2*accel*distance


771.6 m/s / 2 m = 2*accel

accel = 192.90 m/s^2

in terms of g = 19.68 G

So the force acting on your arms in case of an accident @ 100kmph would be

80kg*19.68 = 1574 kgs.

Equivalent to push up with an Innova on your back.

Which nobody's arm can withstand.

So please wear a seatbelt.

Cheers,
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