Vehicle mass: What effet does it have in an accident?

[AussieAV]

Originally Posted by sudszy

Lets see: If the velocity goes from +100km/h to 10km/h in the opposite direction, we have a change in velocity of 110km/h, if it just comes to a stop in then its only a 100km/h change in velocity, that's a higher change in velocity when it "bounces", fairly straight forward isnt it?

the former creates a higher deacceleration (assuming collision time is equal) since acceleration is the rate of change of velocity for both the car and the occupant, assuming of course they are wearing a seat belt.

Claiming "excess" momentum is converted into deacceleration is nonsense. Momentum is not converted into other quantities, it is conserved/transferred shared amongst other bodies in the collision.

Actually sudzy, I think I've just realised exactly where the flaw in your argument is - it's the assumption that collision time is equal. The car can't just travel in the opposite direction instantaneously. At some point its travelling 1km/hr, then 2km/hr etc up to the point of 10km/hr in the opposite direction (as per your example). This can't happen in zero time.

If you dispute this as well, them please PM me and we'll continue the debate in private.

[aussie muscle]

Originally Posted by HULK_BA

Which car will end up better off? A stationary f150 pick up truck or a fiesta hitting it at 150km/h

Clearly the f150 is double its mass?

survivability of an accident has little to with mass and lot to do with forces going through your body and how much it gets flung around the cabin.

[Quicksand]

Originally Posted by WMD351

Here's a couple of threads that have gone into the question (relating to an older bigger car) in much more detail.
http://www.fordforums.com.au/showthread.php?t=11305690
http://www.fordforums.com.au/showthr...6&page=1&pp=30

Before this thread goes any further...i recommend everyone read the above two threads. They are fairly recent and they cover this topic extensively. The threads in question resulted in a lot of fighting, angst and locked threads...there is a wealth of information provided for everyone.

Question: If an empty can of worms crashes with a full can of worms, will this stop the Falcon from being canned?

[cheap]

In this Goliath V's David battle, I would rather be with Goliath.

As well as mass, a 4x4/truck has the added advantage of body height over the little guy. As far as I know and checking various videos NCAP doesn't crash a small car into a truck. The ANCAP/NCAP tests seem to be controlled front and side impacts at set heights.

How representative are these tests are in the real road conditions we face? How many people "plan/control" their collisions to the standards that ANCAP/NCAP expects? Or how many people feel relaxed during their collisions knowing that ANCAP/NCAP is on their side? My point is that ANCAP/NCAP can lead some people to a false scene of security.

If a small car collided with a 4x4/truck there is a likelihood of the small car literally being run over by the higher vehicle. From my perspective broken bones for the occupants within the 4x4/truck seems better than decapitation/crushing for the occupants in the smaller car.

[prydey]

Originally Posted by Quicksand

Before this thread goes any further...i recommend everyone read the above two threads. They are fairly recent and they cover this topic extensively.

the previous threads assume that the larger car is an older car. this thread is asking about the effect of extra mass in a colision. lets assume both cars have modern crumple zones and active safety. then its a different story.

there is a vid on the 1st page of a 5star small car hitting a 4 star audi q7 (i think). 5 stars is only relevant if the object hitting you has a similar mass, give or take.

[NC_Lane]

Originally Posted by prydey

the previous threads assume that the larger car is an older car. this thread is asking about the effect of extra mass in a colision. lets assume both cars have modern crumple zones and active safety. then its a different story.

there is a vid on the 1st page of a 5star small car hitting a 4 star audi q7 (i think). 5 stars is only relevant if the object hitting you has a similar mass, give or take.

That is my question.... Newer cars/4wds have a lot of safety equipment in them..
The question is more to the point of would a say 3 start landcruiser/patrol with airbags be safer than a small 5 star hatch...?

[Quicksand]

Fair enough guys...i still think there is a lot of useful information from those threads to add discussion to this one.

[sudszy]

Originally Posted by NC_Lane

That is my question.... Newer cars/4wds have a lot of safety equipment in them..
The question is more to the point of would a say 3 start landcruiser/patrol with airbags be safer than a small 5 star hatch...?

As has been said many times through the thread, there is no substitute for a mass advantage in a collision.The star ratings have their problems, the frontal impact is with a fixed object, though the side impact one involves the same mass being swung at the vehicles in all tests so they are comparable.

Possibly it would be good to see the actual ratio of one vehicle accident to multi vehicle accidents to decide.

Looking at the big picture, by driving a bigger vehicle to increase our own safety, we actually reduce that of others who continue to drive smaller vehicles. Freedom of choice, perhaps, but where would it end, every one wanting something heavier than the next person to get themselves back a safety advantage?

Its already getting out of control with soccer moms driving around in those 3 tonne porsche,cruiser thingos because hubby likes his bimbo and kids to be safe as she isnt that good a driver.

[xc4me]

Originally Posted by sudszy

you got the forces right, but not the change in momentum/impulse. The change in momentum/impulse(same thing) of the bodies in a 2 body collision is the same in magnitude, opposite direction.

of course, bit of a d'oh moment haha you got me.. it was 1am, what can ya do haha the velocity changes most in the smaller body (could go negative blah blah in order for conservation of momentum... it wont be perfect because this isn't an ideal physics world but you get the point..)
still feeling like a dummy

[WMD351]

Originally Posted by prydey

the previous threads assume that the larger car is an older car. this thread is asking about the effect of extra mass in a colision. lets assume both cars have modern crumple zones and active safety. then its a different story.

True, but the main argument put forth by the old car brigade was primarily related to mass and its effect in a collision so I think it has relevance to this discussion.
As a result that thread (which would probably take days to read from start to finish) contains links to a good amount of information about mass and the laws of physics (but that's all too tekanogical for me).

I'm going to stick with my argument that it's all about how much force is transferred into the occupants bodies and not how much force is put into the vehicles chassis.
All things being equal I think mass wins out, and the point of impact (eg. truck runs completely over roof of car) is entirely relevant, but going on my belief about force being transferred into the human body vs. force being dissipated or absorbed by a crumbling car, consider that a 4WD by design is likely to have a much more ridged and stiffer chassis (therefore less inclined to crumple / absorb / dissipate energy and more likely to transfer the forces into you) owing to the designers misguided belief that at some point the things actually leave Toorak and go off road.

Originally Posted by NC_Lane

The question is more to the point of would a say 3 start landcruiser/patrol with airbags be safer than a small 5 star hatch...?

As I said the stars aren't the be all and end all, they're just a guide. To get all five stars you need to have ABS, ESC, seat belt warning alarms, and other things that are related to avoiding the crash and won't have any effect when it comes to the results of actually having a crash.

Originally Posted by cheap

Or how many people feel relaxed during their collisions knowing that ANCAP/NCAP is on their side? My point is that ANCAP/NCAP can lead some people to a false scene of security.

I thought so too so I started a thread on it.
http://www.fordforums.com.au/showthread.php?t=11306200
The conclusion I drew from that was that it wasn't the ANCAP rating but rather the terrible standards of driver training we have in this country.

If only there was someone here with some first hand experience in these sorts of things who could give us some egsamples of what can happen to 4WDs in a crash, someone who was/is respected by the entire forum not because of some silly smilies but because of the selfless effort and hard work he put into making the forum a better place for all of us...

Originally Posted by Quicksand

Question: If an empty can of worms crashes with a full can of worms, will this stop the Falcon from being canned?

What I'd like to know is why has every old Falcon I've owned had tin worm?

[sudszy]

Originally Posted by xc4me

of course, bit of a d'oh moment haha you got me.. it was 1am, what can ya do haha the velocity changes most in the smaller body (could go negative blah blah in order for conservation of momentum... it wont be perfect because this isn't an ideal physics world but you get the point..)
still feeling like a dummy

No worries, sometimes it just comes out wrong,

[Ford_The_Win]

http://www.youtube.com/watch?v=TBNiQ...eature=related

[geckoGT]

I will predict the outcome of this discussion, it will be the same as all the previous ones.

You can not safely generalise and say that larger cars are safer than smaller cars, there are too many variables and it is the design features and safety systems of the individual cars regardless of size that will determine the survivability of that vehicle an a crash. Added to that, a vehicle that performs well in a frontal crash may be a death trap in a side impact etc. Another thing to consider is that a particular type of vehicle may be safer in a crash compared to a smaller car, but due to elements such as centre of gravity, road holding, braking characteristics etc, that car may be more likely to be involved in an crash which negates the crash survivability. Better off not being in the crash in the first place rather than surviving one.

There too many variables and too much design and tech that can give huge improvements in crash survivability that may not be expected for its size.

Personally, I suggest if you are in the market for a new car, look at the other elements of the car that you require (eg size and features etc) and then look at the safety elements. Large vs small, although an element of safety is not the be all and end all of vehicle safety. Look at it this way, if you had a budget of $25k, what would be safer out of a Fiesta Zetec or a Great Wall 4wd? We all know the answer to that one. The budget of those two examples is about the same, too buy a 4wd that has similar safety to the fiesta, you would have to spend $50k instead of $25k.

[388cube_edxr8]

So what you are saying is that if I buy a Patrol, rebuild the front guards out of 1/4 inch steel plate and build a bullbar made of 2 inch thick solid steel bars, it will be barely any safer in a head on with an Excel than it was from factory.

At some point size and more particularly weight has to play a substantial part in it. Who would be game to drive a 5 star Focus with airbags and crumple zones and stuff into the front of a bulldozer at 50km/h?

[burnz]

Originally Posted by 388cube_edxr8

So what you are saying is that if I buy a Patrol, rebuild the front guards out of 1/4 inch steel plate and build a bullbar made of 2 inch thick solid steel bars, it will be barely any safer in a head on with an Excel than it was from factory.

At some point size and more particularly weight has to play a substantial part in it. Who would be game to drive a 5 star Focus with airbags and crumple zones and stuff into the front of a bulldozer at 50km/h?

if you were to drive both cars at a bull dozer @ 50kph you would survive in the focus..
i serouly doubt you would survive in the patrol with those mods,,youed probably be jellow, every bone shattered from impact transferance.

[geckoGT]

Originally Posted by 388cube_edxr8

So what you are saying is that if I buy a Patrol, rebuild the front guards out of 1/4 inch steel plate and build a bullbar made of 2 inch thick solid steel bars, it will be barely any safer in a head on with an Excel than it was from factory.

At some point size and more particularly weight has to play a substantial part in it. Who would be game to drive a 5 star Focus with airbags and crumple zones and stuff into the front of a bulldozer at 50km/h?

Let me put this scenario at you.

You are driving a 11.54t armoured personnel carrier (APC) surrounded by 50 mm compressed aluminium armour traveling at 60 km when you hit a large immovable tree. The shell of the vehicle suffers almost no deformation and is still usable without any repair required. Despite the seat belt and padded surfaces around you, you still end up with a fractured pelvis, c spine fracture and depressed skull fracture. Why is that?

Now go through the same crash but this time you are driving a brand new fiesta zetec. The vehicle is a complete writeoff and has evidence of the impact all the way through the front, the roof and the doors. This time you walk out with a bit of bruising on your chest from the belt, some abrasions and some mild neck pain but you leave the hospital that night and feel fine a few days later. Why is that?

The simple answer is the both vehicles have been through the same forces, the APC stops immediately, 60-0 in a split second without any force being absorbed by the vehicle structure. The means that as your body slams against the belt and the interior surfaces, it is at full force with no momentum absorbed by the vehicle. In the Fiesta, the crumple of the body increases the pulse time it takes for the force to be applied to the occupants, dissipating much of the energy and therefore decreasing the amount of force applied to the occupants. The car dies so that you may live.

Your modifications to your patrol would only move your chances of survival away from that of a car and closer to that of the APC driver, not a good mod. But at least I guess someone else would be able to fix your car up and use it later, not so good for the occupants though.

[geckoGT]

Originally Posted by burnz

if you were to drive both cars at a bull dozer @ 50kph you would survive in the focus..
i serouly doubt you would survive in the patrol with those mods,,youed probably be jellow, every bone shattered from impact transferance.

Agreed, the focus occupant would be subjected to much less force of impact than the driver of the aforementioned modified patrol.

[wozman]

wood it come down to the people in the car eg old ,young,children weather they live or not?

[geckoGT]

Originally Posted by wozman

wood it come down to the people in the car eg old ,young,children weather they live or not?

Yes to a degree it would, some segments of the demographic deal with vehicle trauma better than others. There is considerable evidence and popular professional opinion is that young children and the elderly, along with other ages in between where the individual has a complicating injury or illness are more likely to die/sustain severe injury in a crash that a person outside those groups would survive. Having said that, vehicle safety mechanisms are designed and tested according to forces applied to the occupant and the expected injury patterns that the average person would sustain as a result. Although in testing a child is simulated individually due to the physical size differences, something that is not seen in an adult age 17-70 and an elderly person.

[cheap]

Originally Posted by burnz

if you were to drive both cars at a bull dozer @ 50kph you would survive in the focus..
i serouly doubt you would survive in the patrol with those mods,,youed probably be jellow, every bone shattered from impact transferance.

The comparison isn't fair.

So lets make it fair and relevant to the original question, if we have a 5 Star 4WD and a 5 Star Focus hit each traveling at 50kph and they have a 'perfect' head-on (just like NCAP). Which would you rather be in and why?

[prydey]

Originally Posted by cheap

The comparison isn't fair.

So lets make it fair and relevant to the original question, if we have a 5 Star 4WD and a 5 Star Focus hit each traveling at 50kph and they have a 'perfect' head-on (just like NCAP). Which would you rather be in and why?

something i've often wondered regarding the ancap testing. logic says the occupants of the similarly rated larger car will be better off, but i'm no physics expert or ancap expert so i'm not 100% sure if thats how it all works.

[WMD351]

Originally Posted by prydey

something i've often wondered regarding the ancap testing. logic says the occupants of the similarly rated larger car will be better off, but i'm no physics expert or ancap expert so i'm not 100% sure if thats how it all works.

I agree with you there prydey. I'd personally advocate buying the biggest and safest car you can if safety's your number one priority, although I'm not a physics or ANCAP novice, let alone expert so it's just my personal opinion.

I pointed out the 4wds high center of gravity earlier and how could be a factor here and if I could poach something from another thread,

Originally Posted by Zedjay

i had a head on with a fiesta in my NP pajero and the chick driving the fiesta wasnt too badly injured...but i havnt worked since have back and shoulder problems.. if you saw the cars you would be like .

she went straight under the drivers side wheel and flipped us over 3 times.

and before anyone wants to reply to this, no I can't find any egsamples of a head on where the badges in the center of the grills perfectly lined up with each other to the millimeter.

[geckoGT]

Originally Posted by cheap

The comparison isn't fair.

So lets make it fair and relevant to the original question, if we have a 5 Star 4WD and a 5 Star Focus hit each traveling at 50kph and they have a 'perfect' head-on (just like NCAP). Which would you rather be in and why?

ANCAP testing bases the majority of its score based on data from accelerometers and load sensors in the Hybrid III crash dummies which gives accurate and consistent injury prediction. Due to this, two vehicles with similar scores in a same crash of equal conditions will offer similar crash survivability.

Everyone needs to remember that a bulk of the assessment under ANCAP comes from the effect on the occupant, not the state of the car afterwards and its ability to be repaired. It is almost true to say that up to a certain force the probability of surviving a crash is inversely proportional to the amount of panel damage. By this I mean at average speeds, new cars with controlled crumple offer more protection from injury than cars with little to no crumple or uncontrolled deformation. I hope that makes sense, it is certainly my observation out at the sharp end of traffic crash scenes.

I have seen people walk out of amazingly crushed wreck with not a mark on them and I have pulled dead bodies out of cars with seemingly little damage, it is all a question of force on the occupant, not the car. Anecdotally, my observation is size has next to nothing to do with it unless you are talking car v bus or car v truck and there is a massive difference in weight.

[cheap]

Originally Posted by geckoGT

ANCAP testing bases the majority of its score based on data from accelerometers and load sensors in the Hybrid III crash dummies which gives accurate and consistent injury prediction. Due to this, two vehicles with similar scores in a same crash of equal conditions will offer similar crash survivability.

Everyone needs to remember that a bulk of the assessment under ANCAP comes from the effect on the occupant, not the state of the car afterwards and its ability to be repaired. It is almost true to say that up to a certain force the probability of surviving a crash is inversely proportional to the amount of panel damage. By this I mean at average speeds, new cars with controlled crumple offer more protection from injury than cars with little to no crumple or uncontrolled deformation. I hope that makes sense, it is certainly my observation out at the sharp end of traffic crash scenes.

I have seen people walk out of amazingly crushed wreck with not a mark on them and I have pulled dead bodies out of cars with seemingly little damage, it is all a question of force on the occupant, not the car. Anecdotally, my observation is size has next to nothing to do with it unless you are talking car v bus or car v truck and there is a massive difference in weight.

Does momentum have any relevance to ANCAP/NCAP?

Forgive me my physics is a little rusty.

A 4WD @ 3000Kg x 50kph = 833333 kg meters / second

A Focus @ 1000kG x 50kph = 277777 kg meters /second

The 4WD has 3 times more momentum than the Focus.

All things being fair and equal, if both the both 4WD and Focus attain 5 star ratings which measures the data from the crash test dummies, wouldn't it be logical to conclude the 4WD has had to provide 3 times the protection to its crash test dummies so that they sustain equivalent damage to that of the crash test dummies in the Focus?

[geckoGT]

Originally Posted by cheap

Does momentum have any relevance to ANCAP/NCAP?

Forgive me my physics is a little rusty.

A 4WD @ 3000Kg x 50kph = 833333 kg meters / second

A Focus @ 1000kG x 50kph = 277777 kg meters /second

The 4WD has 3 times more momentum than the Focus.

All things being fair and equal, if both the both 4WD and Focus attain 5 star ratings which measures the data from the crash test dummies, wouldn't it be logical to conclude the 4WD has had to provide 3 times the protection to its crash test dummies so that they sustain equivalent damage to that of the crash test dummies in the Focus?

In theory yes I suppose it would but there are a number of issues with your question. The first is your weights are way off and over state your example.

The weight of a Nissan Patrol in its heaviest variant is 2638 kg and Ford Focus is 1300 kg, so the difference is not that great, closer to twice the weight and not x3.

Also consider that although the 4 wd has more mass and therefore more kinetic energy to absorb, it also has more metal work and structure to absorb that energy before intrusion to passenger compartment occurs or force is applied to the occupants but the end result is the same.

That is my question.... Newer cars/4wds have a lot of safety equipment in them..
The question is more to the point of would a say 3 start landcruiser/patrol with airbags be safer than a small 5 star hatch...?

The short answer is no because the testing is centered mainly around the forces applied to the dummies. In this case, the 4 wd applied significantly more injury causing force on the dummies than the small hatch did.

There is a good explanation of this here

[Brazen]

Instead of ANCAP smashing cars to an imoveable wall- which is the equivalent of a Fiesta hitting an oncoming Fiesta and a Patrol hitting an oncoming Patrol.

They should smash the car into a oncoming moving object which simulates the average car, ie the Fiesta is now hitting an oncoming object the weight of a Commodore and the Patrol is now hitting an oncoming object the weight of a Commodore.

I think it would be scary to see the difference in ratings...There is probably a bit of social pressure to not do this, as it would just encourage people to buy heavier and heavier cars.

[HLC]

F = ma

Force = mass x acceleration


That says it all really.

[In Focus]

To answer the thread question...

http://www.liveleak.com/view?i=212_1248892696

As to whether small cars are less safe, well other factors come into it, as mentioned earlier in the thread. Another factor overlooked is that, all other things equal, small cars tend to brake more quickly and, often, will be moving at a slower speed at impact.

[cheap]

Thanks for the ANCAP link, here are some interesting FAQ's

Question: If a large, heavy sedan and a small, light sedan both receive five stars and the same ANCAP scores, is the large sedan safer for the occupants than the small sedan?

Answer: It is not appropriate to compare ANCAP ratings across vehicle categories, particularly if there is a large weight difference. The reason is that in car-to-car crashes, the heavier vehicle has a theoretical advantage (due to the physics of the crash). Similarly, a higher ride height might be an advantage in a car-to-car crash. However in single vehicle crashes, such as with solid fixed objects, the weight might no longer be an advantage. So it depends on the type of crash. Also some small cars do remarkably well in crashes with larger vehicles as they have very strong passenger compartments and advanced occupant restraint systems and these features make up for the mass disadvantage.

Question: Is it better to have a small car with a 5 star rating or a medium car with a 4 star rating?

Answer: It is not appropriate to compare ANCAP ratings across vehicle categories, particularly if there is a large weight difference. The reason is that in car-to-car crashes the heavier vehicle has a theoretical advantage (due to the physics of the crash).. Similarly, a higher ride height might be an advantage in a car-to-car crash. However in single vehicle crashes, such as with solid fixed objects, the weight might no longer be an advantage. So it depends on the type of crash. Also some small cars do remarkably well in crashes with larger vehicles as they have very strong passenger compartments and advanced occupant restraint systems and these features make up for the mass disadvantage.

Question: Can ANCAP results be used to compare the relative safety of the vehicles tested?

Answer: ANCAP results can be used to compare the protection offered to occupants in the event of a severe frontal and side crashes for vehicles of similar size and weight. [B]Care must be taken when comparing results for different vehicles as only those vehicles of similar mass can be correctly compared. As a heavier vehicle will generally provide better protection in a collision with a smaller and lighter car, any result comparison should be restricted to cars of a similar class. To assist with the comparison, ANCAP publishes the kerb weight of the cars tested.

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So if you're about to have a collision. Vehicle A is a 5 Star ANCAP rated 4WD/2600Kg and vehicle B is a 5 Star ANCAP rated Focus/1300Kg, both traveling at 50kph and they're about to have an unavoidable head-on crash with each other.

Which car would rather be in, the 4WD or the Focus?

Newton's 2nd law (momentum) is such a wonderful thing.

[sudszy]

Not quite sure what question we want answered or was answered in the last few posts, but if its a focus 1300kg colliding headon with a 4wd-2600kg at 50km/h, then the best case scenario for the focus if it "sticks" to the 4wd is that it would go from 50km/h to 16.6km/h in the opposite direction, a velocity change of 67km/h, or the equivalent of slamming into a concrete barrier at the same speed, probably not survivable.

For the 4wd, it has continued to move forwards at the same speed as the focus stuck to the front:16.6km/h , same thing as hitting a brick wall at 33km/h, very survivable.