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

[NC_Lane]

Hey all,

Been seeing all these articles on how a lot of the new small safe cars are better to be in a crash than in say a 4wd and I have question...

so we say for example that a there is a collision between a small say 1Ton car and a 3Ton 4wd at say 100kmph does it mean that the force encountered is the same for both vehicles?

From what I can gather, wouldn't there be say 3 times more force applied to the car than the 4wd? I would expect the 3Ton 4wd to slow down to a stop in this collision and the car to end up going backwords..

Does this sound right/can someone clarify?

Cheers,

[Revolver]

All I can comment on is the speed at which they hit.

If they are both doing 100, then the speed of impact (Head on) is 200kmph.

There maybe some form of calculations to clarify the force of the impact wieght wise. But yes logically speaking, the odds would be in the superior mass.

Thats why you never pick o a bloke 3 times the size of you.

Never **** with a superior mass.......

[EgoFG]

Mass is interesting.
Larger mass means more energy that needs to be absorbed (or deflected)
If you have a significantly larger mass and greater rigidity then you can make all of the energy get transferred to the other vehicle (I used to polish the datsuns off my Chrysler by Chrysler) - this is why we win when we hit an insect.
But if we have more mass, and greater rigidity then it is worse if we crash into an immovable object (tree).

So it is a balance - resist crumple to avoid small amounts of damage, but crumple all except the passenger cell in a larger accident.

It could be that a lighter car needs better crumple control as it will be more objects will be, from its perspective, immovable.

So it really depends on what you plan on running into.

I think a large mass car with a High Ancap rating, and avoid crashing into anything larger than you.

Originally Posted by Blue Beast II

If they are both doing 100, then the speed of impact (Head on) is 200kmph.

This is correct, but the accident is no worse than two cars crashing into two walls at 100 kmph. There was a mythbusters ep on this.

[flappist]

Originally Posted by Blue Beast II

All I can comment on is the speed at which they hit.

If they are both doing 100, then the speed of impact (Head on) is 200kmph.

There maybe some form of calculations to clarify the force of the impact wieght wise. But yes logically speaking, the odds would be in the superior mass.

Thats why you never pick o a bloke 3 times the size of you.

Never **** with a superior mass.......

Unfortunately your comment in completely wrong

If they are both doing 100km/h the the impact is 100km/h NOT 200km/h.

The impact speed for each object is the difference between what each object is doing before the crash and what they are doing immediately after the crash.

The 200km/h is a common misunderstanding.....

[Yellow_Festiva]

Originally Posted by flappist

Unfortunately your comment in completely wrong

If they are both doing 100km/h the the impact is 100km/h NOT 200km/h.

The impact speed for each object is the difference between what each object is doing before the crash and what they are doing immediately after the crash.

The 200km/h is a common misunderstanding.....

This was my understanding of the matter. Both vehicles, if square and head on will essentially be hitting a brick wall (so to speak).

Could be wrong of course... not the first time lol

[DBourne]

edit: beaten

[sgt_doofey]

It's simple Physics, but unfortunately, it's been quite a number of years since I did it at high school. The 3T 4wd will exert more force on the lighter 1T car due to it's mass.
Force = mass x acceleration

[sudszy]

Originally Posted by sgt_doofey

It's simple Physics, but unfortunately, it's been quite a number of years since I did it at high school. The 3T 4wd will exert more force on the lighter 1T car due to it's mass.
Force = mass x acceleration

You've forgotten newton's 3rd law, the forces on each will be of exactly the same magnitude but in opposite directions.

Since the force on each is the same, then the object with the higher mass will suffer less acceleration, newton's 2nd law.
Basically in any two or more vehicle collision, higher mass vehicle suffers the less change in speed and is more survivable for the occupants.

[NC_Lane]

So does that mean that in theory (as long as your NOT smashing into concrete barriers) a 3Ton 4wd is safer than a 5star hatch?

[Yellow_Festiva]

Originally Posted by NC_Lane

So does that mean that in theory (as long as your NOT smashing into concrete barriers) a 3Ton 4wd is safer than a 5star hatch?

You are mixing 2 variables there, weight and safety.

What is the age / construction / condition of the 4wd? The 4x4 my fare better in an accident, but the occupant may smash their head on the wheel rather than the airbag of the smaller hatch.

How safe a car is depends on sooooooo many factors.

[13101093]

what needs to be considered here is decelaration, thats what causes injuries in a car accident, if you had a 3 ton fourby that was solid as, you hit a concrete wall, your going to bounce around inside, or hit your seatbelt pretty hard, and the car will probably bounce off the wall. if you hit it in a 1 ton small car with proper crush zones etc, the car will crumple around you and all the energy is taken up by the car and not by you.

[NC_Lane]

Originally Posted by 13101093

what needs to be considered here is decelaration, thats what causes injuries in a car accident, if you had a 3 ton fourby that was solid as, you hit a concrete wall, your going to bounce around inside, or hit your seatbelt pretty hard, and the car will probably bounce off the wall. if you hit it in a 1 ton small car with proper crush zones etc, the car will crumple around you and all the energy is taken up by the car and not by you.

Woops missed the NOT in my above post. Fixed now

[Geez Louise]

Originally Posted by 13101093

what needs to be considered here is decelaration, thats what causes injuries in a car accident, if you had a 3 ton fourby that was solid as, you hit a concrete wall, your going to bounce around inside, or hit your seatbelt pretty hard, and the car will probably bounce off the wall. if you hit it in a 1 ton small car with proper crush zones etc, the car will crumple around you and all the energy is taken up by the car and not by you.

I was just thinking that myself. Different cars have different crumple zones, therefore changing the results.

[tik-4d]

if both vehicles are travelling at 100 kph and collide head on, the total force will be equal to a crash at 200 kph, however because the two vehicles each weigh differently, the force of the impact is spread accordingly.

using momentum (mass)x(final velocity) and (mass)x(initial velocity) you can calculate the change momentum of each vehicle and thus finding the final veloctiy after the crash.

on a head on collison (mass)x(final velocity) and (mass)x(initial velocity) of one vehicle must eqaul the same of the other vehicle, then we can find the unknown variables in the eqaution.

from my calculations, just after the impact the 3ton 4wd is still travelling at 20.85 m/s while the 1ton hatchback is travelling at 13.9 m/s in the opposite direction. during the impact, the 4wd will exert a net result of twice the momentum of the hatchback.

i could be wrong though i'm pretty sure i'm right, don't hold me to it.

[flappist]

Originally Posted by tik-4d

if both vehicles are travelling at 100 kph and collide head on, the total force will be equal to a crash at 200 kph, however because the two vehicles each weigh differently, the force of the impact is spread accordingly.

using momentum (mass)x(final velocity) and (mass)x(initial velocity) you can calculate the change momentum of each vehicle and thus finding the final veloctiy after the crash.

on a head on collison (mass)x(final velocity) and (mass)x(initial velocity) of one vehicle must eqaul the same of the other vehicle, then we can find the unknown variables in the eqaution.

from my calculations, just after the impact the 3ton 4wd is still travelling at 20.85 m/s while the 1ton hatchback is travelling at 13.9 m/s in the opposite direction. during the impact, the 4wd will exert a net result of twice the momentum of the hatchback.

i could be wrong though i'm pretty sure i'm right, don't hold me to it.

This has been done to death several times.

The 200km combined crash speed IS COMPLETELY MISLEADING and is commonly used by "road safety freaks" to beat up an emotional reaction.

There is almost no difference between a vehicle hitting a brick wall at 100km/h and hitting an oncoming vehicle of similar mass at 100km/h.

If the oncoming vehicle has a greater mass them the first vehicle will be accellerated backwards.

For it to be a 200km/h crash the first vehicle would have to be accellerated to 100km/h in the opposite direction........

[tik-4d]

i clearly state the total force of the impact, as in the total force of the system is equal to a crash at 200 kph as both cars have a crash, both doing 100 kph.

[flappist]

Originally Posted by tik-4d

i clearly state the total force of the impact, as in the total force of the system is equal to a crash at 200 kph as both cars have a crash, both doing 100 kph.

Your statement is very misleading but I suspect you already knew that.....

http://www.fordforums.com.au/showthread.php?t=11282496

[sudszy]

Originally Posted by tik-4d

i clearly state the total force of the impact, as in the total force of the system is equal to a crash at 200 kph as both cars have a crash, both doing 100 kph.

No, apply Newton's 3rd law to the situation.
Consider car A going to the right versus car B going to the left each doing 100km/h

Car A is brought to a halt by a force of magnitude F acting on it in the opposite direction to its travel, this force to the left comes from car B

Similarly car B's motion to the left is arrested by a force F acting to the right, from car A. Equal and opposite forces, or sum of the magnitude of the two forces = 2F.

Consider car A travelling right into wall at 100km/h
Car A experiences a force to the left of force F to arrrests its motion, the change in speed is exactly the same as above (100 to whatever speed they bounce of each other) hence the force is the same.
The wall experiences a force of F from the car pushing it to the right
Mag of total forces = F + F =2F

the forces are exactly the same, though the amount of damage is clearly double when two vehicles are involved.

[EgoFG]

Originally Posted by flappist

There is almost no difference between a vehicle hitting a brick wall at 100km/h and hitting an oncoming vehicle of similar mass at 100km/h.

In fact, if your choice is between a tree/wall, and oncoming car YOU would be almost safer to take the oncoming car - but it may actually have people in it.

Interestingly from a legal perspective, if the oncoming car is in the wrong, and you have a choice to run into it or a wall - your insurance will have to pay if you choose to run into the wall (assuming that the other car avoids the collision).

[jpd80]

Originally Posted by flappist

This has been done to death several times.

The 200km combined crash speed IS COMPLETELY MISLEADING and is commonly used by "road safety freaks" to beat up an emotional reaction.

There is almost no difference between a vehicle hitting a brick wall at 100km/h and hitting an oncoming vehicle of similar mass at 100km/h.

If the oncoming vehicle has a greater mass them the first vehicle will be accellerated backwards.

For it to be a 200km/h crash the first vehicle would have to be accellerated to 100km/h in the opposite direction........

I finally got this concept a while ago, the laws of conservation of momentum can only
be bent in the universe of politics and road safety when calling for more speed cameras....

I am surprised that this sleight of hand hasn't been openly busted by scientists,
maybe the do-gooder road campaigners are worried that their other silver bullet,
50 kph vs 60 kph braking distances will come under even more scrutiny and dispelled...

[prydey]

this is a touchy subject for many people, but i think its worth considering. the ancap ratings get marketed reasonably hard by most manufacturers but personally i think they can only be compared accross a similar category of vehicle.

just because your buzz box is 5 star, doesn't make it safer than a 4 star 4wd.

sometimes i think its an argument that will never end. some say 5star is 5 star which is safer than 4star, regardless.


most of these questions get raised on youtube but most of the time, they compare old cars with new cars. there aren't many tests that compare new large cars with new small cars. mass is still king.

a ba/bf falcon will probably still be safer than a hyundai i30. ones 5 star, ones 4 star.

[GasoLane]

Originally Posted by prydey

just because your buzz box is 5 star, doesn't make it safer than a 4 star 4wd.

Prydy is on the money. I drive a no star Volvo, but I'll take on any 5 star car

[sudszy]

Originally Posted by tik-4d

, then we can find the unknown variables in the eqaution.

from my calculations, just after the impact the 3ton 4wd is still travelling at 20.85 m/s while the 1ton hatchback is travelling at 13.9 m/s in the opposite direction. during the impact, the 4wd will exert a net result of twice the momentum of the hatchback.

i could be wrong though i'm pretty sure i'm right, don't hold me to it.

Wont hold you to it, but it isnt correct.

if you do the numbers on yours, the smaller vehicle has suffered a great momentum change than the larger vehicle, which isnt in accordance with laws of physics which predicts that the momentum changes should be equal in magnitude and opposite in direction.
Its also impossible to predict the speeds of the vehicles after the collision unless you know the elasticity of the materials involved, the characteristics of the crumple zones of the two vehicles etc.

[jpd80]

In the worst case, a head on between two vehicles travelling at 100 kph will only ever reduce
the forward velocity to 0 kph, this is the maximum deceleration that can be applied to either vehicle,
any remaining momentum is then expressed as either a forward or negative velocity after impact.

[sudszy]

Originally Posted by jpd80

In the worst case, a head on between two vehicles travelling at 100 kph will only ever reduce
the forward velocity to 0 kph, this is the maximum deceleration that can be applied to either vehicle,
any remaining momentum is then expressed as either a forward or negative velocity after impact.

No, if the vehicles bounce back of each other(even with today's crumple zones, they will bounce off each by a few km/h), then the deacceleration will be higher.

[mikestp]

The safety of a single vehicle hitting an immovable object will depend almost entirely on the design of the vehicle, A heavier vehicle will have no real advantage because the deceleration is the same (Vehicle speed - 0) The design of crumple zones is very important for this to make the deceleration occur over the largest distance possible (without deformation to cabin area).

However in a 2 car collision the inertia of the vehicle is as important as the vehicles design. If a 1 ton car has a head on with 2.5 ton 4wd the deceleration for the 2 vehicles is not the same, The 4wd will most likely drag the car backwards.
So acceleration force on the occupants of the 4wd will be lower (cruising speed - zero over a decent distance) compared to the car (cruising speed to backwards in the blink of an eye)

Conclusion:
Id take the landcruiser over the 5 star ANCAP roller-skate anyday

[bigsta]

Its simple physics really.

First when hitting a immovable object in a bigger car there is more crumple zones and more metal to adsorb the impact as well as room for engine bits and steering racks to go before the force and said steering racks make their way to you.

When a 3t car hits a 1 ton car this is where the physics are really on your side in the big car as your momentum and force is repeatedly adsorbed by the smaller mass vehicle so in a sense you are pushing into them and using their crumple zones where as the small vehicle is experiencing more of a impact with a concrete wall as they are not only adsorbing the impact from their kinetic energy but the big cars as well. This is why its quite common to see in a impact between a 4WD or a truck and a smaller car the 4wd has almost no damage but people are being cut out of the excel.

There is a few variables that can change things such as speed angle of impact etc the worse possible accidents are those that stop you dead on such as a head on or a t bone.

[OLDFORDNUT]

Originally Posted by bigsta

Its simple physics really.

First when hitting a immovable object in a bigger car there is more crumple zones and more metal to adsorb the impact as well as room for engine bits and steering racks to go before the force and said steering racks make their way to you.

When a 3t car hits a 1 ton car this is where the physics are really on your side in the big car as your momentum and force is repeatedly adsorbed by the smaller mass vehicle so in a sense you are pushing into them and using their crumple zones where as the small vehicle is experiencing more of a impact with a concrete wall as they are not only adsorbing the impact from their kinetic energy but the big cars as well. This is why its quite common to see in a impact between a 4WD or a truck and a smaller car the 4wd has almost no damage but people are being cut out of the excel.

There is a few variables that can change things such as speed angle of impact etc the worse possible accidents are those that stop you dead on such as a head on or a t bone.

Thank you, i was about to write the same thing.

[GasoLane]

Lets face it. If it's your turn to die, nothing you're driving will stop it.

[colinl]

Originally Posted by GasOLane

Lets face it. If it's your turn to die, nothing you're driving will stop it.

In the words of Tony Abbott, "**** happens". But often it is a result of a number of factors leading up to it. I tend to enjoy riding motorcycles in a spirited manner, and have come off a few times doing this. I have no doubt that in these cases I would have been very badly injured or killed if I hadn't made the choice to wear full leathers, body armour, decent gloves and boots. It is certainly true that despite everything, you may die; but why increase the risk through making poor choices.