Go Back   Team-BHP > Under the Hood > Technical Stuff


Reply
 
Thread Tools Search this Thread
Old 24th October 2012, 14:33   #1
BHPian
 
torquecurve's Avatar
 
Join Date: Oct 2009
Location: Pune
Posts: 598
Thanked: 629 Times
Default Understanding Seat Belts : Layman Language

Hi Everyone,

I am starting this thread to make an attempt at explaining why we need those safety features and what all the Automotive Jargon means in layman terms.

The reasons for doing this are manifold.
1. I have seen some people on this same forum, questioning the need for seat belts. Some are open enough to accept they dont wear it, while some don't want to get beaten up by others.
2. There are many who have gone for tyre upgrades, light upgrades etc, in some cases without considering the dangers that it can bring in.
3. To dispel the attitudes that we have towards our own and others safety.
4. Sometimes, it is important to show the mirror, some may not still see reason, but if I help save even one life, I think the effort is worth it.

While I am no guru I certainly feel it is important to explain these things in as easy language as possible.

I will start this series with a simple topic of Seatbelts.



Seatbelts

A brief history -
The earliest cars didn’t have seatbelts, derived as they were from Horse drawn carriages. They didn’t even have rubber tyres!
In the early 1950's seatbelts were introduced in cars as speeds went up and accidents led to many deaths with a high number of people crashing into the steerings, hard dashboards and the like.
In the 1970's it became mandatory for people in some US states to wear seat belts. Insurance companies, soon realising how it saved lives, lobbied the government to make it mandatory and the rest as they say is history.

What does a seatbelt do?
A seatbelt, also called safety belt, is designed to hold you back in your seat in case of a sudden deceleration (read slowing down) of your car. The Three way strap of the seatbelt is designed to move the forces caused away from your body into the frame of the car. This is the basic premise of the seat belt.

Okay, but why wear it? As a driver I can just hold on to the steering wheel which will stop me from banging into the steering wheel. The passengers can wear it, I don’t need to.

Note: This comment is from a very recent post on the Accidents in India/Bad drivers thread.
Seatbelts don’t just help in case of accidents, they also help when you suddenly have to slow down (e.g. another vehicle/ person comes in your way).
About holding on to the steering wheel, okay, I am going to use some physics (basics) to explain why this is not safe.
Lets say you are driving at a speed of 60 Kmph. You weigh about 80 Kgs (I weigh 100 ) And you suddenly have to slow down (Brake) from 60 to 0 kmph very quickly and this happens in 1 seconds. 60 Kmph = 16.67m/s
Simple physics - Force = Mass X Acceleration(Deceleration)
To calculate Decelaration I use another formula = (0-16.67)/1 = -16.67 m/s square.
So the total force exerted is about = 80x16.17 = 1293.6 (Newtons)
Okay before you say, this is not laymans language, I will try to make sense of these numbers.
I have considered that your car is braking (not crashing) just to show what are the effects of this. 1293.6 Newtons of force is approximately equal to a weight of about 132 Kgs kept on the ground. Imagine that on your hands in this case).
If you change the weights, you get the below (for same speeds).

At 100 kgs, the force is 100X16.17 = 1617 N (165 Kg weight!)
At 90 Kgs, the force is 90 x 16.17 =1455 N (~150 kg weight!).

To give you an idea of the force
"An oft-cited 1985 study of Frank Bruno, who'd go on to be WBC heavyweight champ, showed he could punch with a force of 920 pounds in the lab. Researchers extrapolated that to a real-life blow of 1,420 pounds, enough to accelerate his opponent's head at a rate of 53 g -- that is, 53 times the force of gravity." 1420 foot pounds is almost 6000 Newtons! (Wolfram-Alpha).
"Another study found martial artists needed 687 pounds of force to break a concrete slab 1.5 inches thick. " this is almost 3000 N.

http://www.connectsavannah.com/news/article/102548/

I dont think my bones are as strong as concrete, or neither do I train to be a martial artist/ boxer. My bones can easily fracture under these stresses. So unless you are, well.
Many times, you will not get major fractures but there will surely be minor stress fractures which sooner or later will lead to major issues. The seatbelt in this case will take this force and transmit it to the body shell of the car through the B-Pillar and the lower support strut. The car is designed to take this kind of force.

Another thing, with increase in speed, this factor changes drastically.
For an 80 kg person in a car at
80 kmph the force is 80 X 22.22 = 1776 N and at
100 kmph = 80 X 27.77 = 2221 N

This is Way beyond what your hands can support and can easily break your hands. And I am considering just Braking.

In case of a collision the speed reduces from 60 to 0 in a few milliseconds. (consider 10 ms) then the force is
Decelaration (0-16.67)/0.10=-166.7 (note that this is literally increased by 10 times)

Force = 13336 N! for an 80Kg body.

Which is almost equal to the weight of 1360 Kgs lifted! Or four martial artists hitting you at the same time. Now can you handle that kind of energy?

I know this sounds like a lot of Jargon and I promised to make it into layman terms. But the fact of the matter is a seatbelt will save you in case of a crash or even when there is a quick slowdown.

Can a seatbelt injure me?
Surprisingly, the answer is "Yes". Look at the calculations I have done here, the forces are massive. Some of them are going to be transmitted to your body (in a crash), the forces of a slowing vehicle are easily absorbed. Also as it happens over a longer period (yes 1 second is a pretty long time) the seatbelt is easily able to dissipate the energy.
In a crash, the seatbelt does not have enough time to contain and dissipate the forces also the vehicle body is already under strain to dissipate the other forces of the crash. But, remember this in case you don’t wear it the ENTIRE force is transmitted to your body. Most people wearing a seatbelt will at the most have cracked ribs or a dislocated shoulder. Injuries which will heal over a few weeks. But yes, the chances of survival are increased a LOT!.
Statistics show that Risk of fatal injury reduces by about 45% for a person on the front seat wearing seat belts. More than 55% of people involved in otherwise minor collisions and not wearing seatbelts have had critical or fatal injuries.
Also, improperly worn, old, frayed seatbelts can do a lot of harm. Do not attach anything to the seatbelt. (Pins, clips, seat belt covers etc).

Please see the videos below, one more reason why and how seat belts save you.





For people who say, "when my time comes even a seatbelt will not save me". Just one thing, don't tempt fate please. Just imagine if your "time" is yet not come and because of a debilating injury you have to be bed ridden for the rest of your life.

My signature has a message - It is not just the people who you injure that you hurt, you never know how many people (our families included) will be hurt, emotionally or physically.

Seat belts save lives. Please wear them.

And, yes, they come for free with the Car, why not use it if it is free?

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

Last edited by torquecurve : 27th October 2012 at 18:11. Reason: Adding an image of a seat belt :), Added couple of videos and made some corrections.
torquecurve is offline   (68) Thanks Reply With Quote
Old 25th October 2012, 12:51   #2
GTO
Team-BHP Support
 
GTO's Avatar
 
Join Date: Feb 2004
Location: Bombay
Posts: 47,700
Thanked: 89,136 Times
Default Re: Understanding Seat Belts : Layman Language

Thread moved from the Assembly Line (The "Assembly Line" Forum section) to the Technical Section. Thanks for sharing!
GTO is offline   (2) Thanks Reply With Quote
Old 25th October 2012, 16:28   #3
BHPian
 
Abhi_abarth's Avatar
 
Join Date: May 2012
Location: Hyderabad
Posts: 330
Thanked: 111 Times
Default Re: Understanding Seat Belts : Layman Language

Thank you for this wonderful information torquecurve. This should be more than enough for any person to understand the significance of a seat belt.

Sadly, in our country even a person who tries to educate people to wear a seat belt is laughed at.

The bottom line is pretty simple "Seat belts saves life"
Abhi_abarth is online now   Reply With Quote
Old 25th October 2012, 16:32   #4
Senior - BHPian
 
Swanand Inamdar's Avatar
 
Join Date: Jan 2011
Location: Chicago, IL
Posts: 1,648
Thanked: 573 Times
Default Re: Understanding Seat Belts : Layman Language

The point torquecurve is trying to make is, wear your seatbelts. Regardless of the weight, the speed, the time taken to stop etc etc.
Just wear the belt!

Quite an important topic torqucurve. .

Last edited by noopster : 29th October 2012 at 09:15. Reason: Thanks! Opening post corrected now
Swanand Inamdar is offline   Reply With Quote
Old 25th October 2012, 17:30   #5
Senior - BHPian
 
rohanjf's Avatar
 
Join Date: Nov 2009
Location: Adelaide
Posts: 1,190
Thanked: 684 Times
Default Re: Understanding Seat Belts : Layman Language

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?
rohanjf is offline   Reply With Quote
Old 25th October 2012, 17:48   #6
BHPian
 
AlphaKilo's Avatar
 
Join Date: Nov 2010
Location: VOMM-EDDW-EDDM
Posts: 773
Thanked: 362 Times
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?
No!
Excuse me if I sound like a nerd here. Remember, first law of newton? Inertia? Braking with ABS or without it doesn't matter for inertia. Its just a change of your state of motion, irrespective of the fact whether you come to a screeching halt or a halt! The amount of energy you dissipate is the same irrespective of the way you loose it.(unless and otherwise ABS makes the car stop like we normally do!)

Last edited by noopster : 29th October 2012 at 09:16. Reason: Thanks! Opening post edited suitably
AlphaKilo is offline   Reply With Quote
Old 25th October 2012, 18:03   #7
Team-BHP Support
 
noopster's Avatar
 
Join Date: Feb 2010
Location: Pune
Posts: 8,665
Thanked: 9,192 Times
Default Re: Understanding Seat Belts : Layman Language

A stop from 60 kmph to rest in 1 second (OP's scenario) would be the equivalent of being sat on very suddenly by a person weighing 136 kg!!!

Please check this link: explains the math behind it much better than I can.

By my calculations, a hard stop from 60 kmph without seatbelts is the equivalent of a jump from a 45 feet high building.

All said and done, whatever the maths behind it, the key thing to remember is that seatbelts do save lives, even at moderate speeds. It is very distressing to see ignorant points of view paraded as rational choices on these forums and elsewhere. THis thread is a timely reminder for all of us to buckle up! And drive safe.

Last edited by noopster : 29th October 2012 at 10:52.
noopster is offline   (4) Thanks Reply With Quote
Old 25th October 2012, 18:13   #8
BHPian
 
AlphaKilo's Avatar
 
Join Date: Nov 2010
Location: VOMM-EDDW-EDDM
Posts: 773
Thanked: 362 Times
Default Re: Understanding Seat Belts : Layman Language

Quote:
Originally Posted by noopster View Post

Please check this link: explains the math behind it much better than I can.
THis thread is a timely reminder for all of us to buckle up! And drive safe.
Fantastic link Noops sir. Especially, I love this part:

Quote:
If you fell off a 12 story building it be nice if you could hit a thick air-filled mattress? One that collapsed with a whoosh and brought you to a stop?
In fact people can survive stops from 200 km/hr, 120 mph if their stop is done in a 1 meter, 3 foot, distance and if the force is spread uniformly over their bodies. Terminal velocity for a human body in the parachutist's free fall position, face down,with body arched, is 200 km/hr or 120 mph. People have survived 10,000 foot, 3000 m, falls out of airplanes into powder snow. They are found, intact, at the bottom of a 1 meter deep crater...


The seat belt stops you. It is like jumping and being caught by a wide nylon strap after a 140 foot fall. Better than hitting steel and glass, but not as good as an airbag.
Wish our Govt. enforces this rule seriously!

With seat-belt pretensioners, I feel even more safer than earlier version of seat belts. What more in terms of technology is possible that could be implemented in this humble life saving device?

Last edited by AlphaKilo : 25th October 2012 at 18:17.
AlphaKilo is offline   (1) Thanks Reply With Quote
Old 25th October 2012, 19:11   #9
BHPian
 
Join Date: Nov 2007
Location: Pune
Posts: 574
Thanked: 159 Times
Default Re: Understanding Seat Belts : Layman Language

I have a question here. In road cars, we have airbags other than seatbelts. But the race cars like F1 or Nascars, only the seatbelts do the job. Why don't they need airbags while they travel at much faster speed and involved in crashes that are much higher in severity.
shipnil is offline   Reply With Quote
Old 25th October 2012, 19:29   #10
Senior - BHPian
 
ecenandu's Avatar
 
Join Date: Oct 2008
Location: Guruvayoor/Chen
Posts: 1,024
Thanked: 1,472 Times
Default Re: Understanding Seat Belts : Layman Language

Quote:
Originally Posted by shipnil View Post
I have a question here. In road cars, we have airbags other than seatbelts. But the race cars like F1 or Nascars, only the seatbelts do the job. Why don't they need airbags while they travel at much faster speed and involved in crashes that are much higher in severity.
Because in race cars they are not using a 3point seat belt but a 5 point one. Once properly strapped in those your body won't move an inch. It will be impractical to use those for daily purpose.
ecenandu is offline   Reply With Quote
Old 25th October 2012, 19:51   #11
Senior - BHPian
 
Join Date: Apr 2008
Location: Bangalore
Posts: 2,534
Thanked: 984 Times
Default Re: Understanding Seat Belts : Layman Language

Quote:
Originally Posted by shipnil View Post
Why don't they need airbags while they travel at much faster speed and involved in crashes that are much higher in severity.
Along with what ecenandu has already mentioned, the cockpit of the F1 cars are built to withstand some serious impact and still protect its occupant.
abhinav.s is offline   Reply With Quote
Old 25th October 2012, 20:03   #12
BHPian
 
Join Date: Jan 2012
Location: Bangalore,Coorg
Posts: 790
Thanked: 361 Times
Default Re: Understanding Seat Belts : Layman Language

Torquecurve, we can only hope that some people read this and are convinced and use their seatbelts regularly. For me I used seatbelts initially because it was mandatory in Africa, and then realized just how useful it was. Now it is habit for me to use my seatbelts wherever and whenever I drive. I try to get everybody in my car to use it as well but it is not easy. Too many people are disinterested.

@abhinav.s - most cars today are designed to take the impact of accidents. That is what the modern day design of crumple zones and passenger cells are for. Yes, the f1 cars can take a lot more. But understand, the point of seatbelts and airbags is that the person is held back in place and if he does hit something it is soft rather than hard. The reason f1 cars don't have airbags is two fold. First the seatbelts are designed and used in such a way that the person does not move. Therefore, the airbag becomes redundant as the person won't hit the airbag, unless it inflates enough to hit him, which is actually more dangerous than useful. Secondly, from a weight perspective, it makes very little sense for an f1 car. They literally count every gram of weight.

Last edited by pganapathy : 25th October 2012 at 20:11.
pganapathy is offline   (1) Thanks Reply With Quote
Old 25th October 2012, 20:12   #13
Distinguished - BHPian
 
Join Date: Jul 2009
Location: Kolkata
Posts: 3,506
Thanked: 2,071 Times
Default Re: Understanding Seat Belts : Layman Language

^^^
Also look up HANS.


Regards
Sutripta

Last edited by noopster : 29th October 2012 at 10:53. Reason: Original post edited thanks
Sutripta is offline   Reply With Quote
Old 25th October 2012, 20:38   #14
BHPian
 
Join Date: Jun 2009
Location: Pune
Posts: 90
Thanked: 28 Times
Default Re: Understanding Seat Belts : Layman Language

Great article torqueCurve.
Yeah, it's difficult to explain to people that it saves lives. But even in cases of hard braking, it can save you minor (comparatively) injuries which is worth it.

Some of the reasons I have heard are
1) It causes crease in my shirt
2) It doesn't let me move freely in the car
3) Agar time aa gaya to jaana hi padega, yeh thodi bachaaega ( if my time has come [to die], then this seat-belt wont stop it)
4) Don't wear it, no policeman has the guts to fine me
I just roll my eyes.

If it's my car the rule is simple, it won't move ahead till passengers in both seats are strapped in.
jaygeetee is offline   Reply With Quote
Old 26th October 2012, 06:52   #15
Senior - BHPian
 
shankar.balan's Avatar
 
Join Date: Apr 2008
Location: BLR
Posts: 8,027
Thanked: 5,325 Times
Default

Quote:
Originally Posted by pganapathy
Torquecurve, we can only hope that some people read this and are convinced and use their seatbelts regularly. For me I used seatbelts initially because it was mandatory in Africa, and then realized just how useful it was. Now it is habit for me to use my seatbelts wherever and whenever I drive. I try to get everybody in my car to use it as well but it is not easy. Too many people are disinterested.
I wonder why we in India have even more primitive and archaic rules and enforcement than the chaps out there in Africa.
I insist that everyone in the vehicle wears their seat belts. The front passenger most certainly ( no getting away because the warning light and sound keeps on at it to remind one to wear the belt), and the rear passengers because it is simply safer. However, there are very few occasions where we have four people in the vehicle.
I will not allow 5 people in my car because it is too much of a tight squeeze.
shankar.balan is offline   (1) Thanks Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
5-point Harnesses / Belt-In-Seat seat belts in Road Cars? Brute_force Modifications & Accessories 10 18th February 2013 13:38
Expressway Tragedy: Bad Management and Importance of seat belts... EVO6 Street Experiences 50 16th February 2006 16:10
This is why you should fasten you Seat Belts. epyupc Shifting gears 17 15th July 2005 14:25
I Pledge.. I will always wear seat belts greatDrive Street Experiences 13 14th June 2005 17:08
Seat Belts for women normally_crazy Shifting gears 8 13th September 2004 00:55


All times are GMT +5.5. The time now is 15:02.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks