Car physics

[Franco Cozzo]

I was wondering about this just before and I can't remember any of my yar 11 physics stuff, but would hitting a solid imovable object at 100km/h be worse than hitting another car head on also travelling at 100km/h?

[1LOUDXFUTE]

yes, hitting an omcoming car travelling at 100km/h is alot worse, almost as bad as hitting a solid object at ~200km/h

[Dave R]

Hitting the other car... it's like hitting the solid object while it's travelling 100km/h at you, double the force!

[Chopped]

It would be the same either way.

[Maggot]

^Agreed

You are always better off hitting a car that can move and has a crumple zone than hitting something solid and immovable (solid concrete block).. but if the oncoming car is going the same speed as you and is the same mass, then it wouldn;t make much difference.. you would be dead either way.

[geckoGT]

Originally Posted by Maggot

^Agreed

You are always better off hitting a car that can move and has a crumple zone than hitting something solid and immovable (solid concrete block).. but if the oncoming car is going the same speed as you and is the same mass, then it wouldn;t make much difference.. you would be dead either way.

True in a way, the effect is devastating.

The thing is the question was not really about injury patterns but rather is was about the physics of the matter.

A "solid" object suggests one with no crumple zones and he asked about one that is immovable. So your vehicle has crumple zones which will decrease the impact but not to a survivable level. In fact most cars do not provide much survivability in any impacts greater than 60-70 km/h.

Now, assuming the scenario of another vehicle also traveling at 100 km/h in a head on is the same type of vehicle with similar mass and crumple zones. The impact would not be exactly equivalent to hitting a solid immovable object at 200 km/h as has been suggested. There are two main reasons for this, firstly the other car is not immovable and will deflect or rebound to an extent, thereby reducing impact force at the collision point and dispersing it into another direction. Secondly the other car also has crumple zones, therefore vehicle deformation absorbs energy. A solid, immovable object provides neither of these. To illustrate the concept of crumple zones, what will have more force at the point of impact, two pillows colliding at 100 km/h or two bricks (of equal mass to the pillows), of course it is the two bricks.

Now all this does not mean that the forces on the subject vehicle is equal in the car vs solid object at 100 and the car vs car at 200. The car vs car will have considerably more force at point of impact than car vs solid object.

Given the choice, I would take neither.

[Maggot]

The thing he was asking is which is worse..and the fact is that hitting a completely immovable and solid object at 100, and hitting an oncoming car of the same mass and speed as you actually will have the SAME affect on you.. as the rusultant decelleration will be the same.

If the other vehicle is smaller than you then you are always better of hitting it than a solid wall..

[GTP owner]

Maggot got it right. Two cars of exactly the same type and mass hitting each other at 100km is NOT equal to a 200km/h collision. If your car weighed substantially less than the opposing vehicle (say you are a barina and they are a truck) and you go backwards as a result of the collision at 100km/h, then, and only then is the force equivalent to a 200km/h collision.
So two equal cars colliding will have exactly the same crumple zones, so will be exactly the same as hitting a brick wall. There will be no reduction in force as a result of their crumple zone giving way unless you weigh more than they do.
This is why it is seen as safer for you to have a heavier car (as in a 4x4) because more of the force is transferred to the smaller car - ie. they go backwards, while you do not completely stop. As an example - you have a landcruiser and they have a barina. They will go backwards at 20km/h, meaning their impact is the equivalent of a 120km/h collision, which is unsurvivable. The cruiser decelerates to 20km/h, meaning the force is of a 80km/h collision, which will probably be fatal.

[LTDHO]

I disagree.

Hiting object at 100kpm will not be as bad as hitting an oncoming object @100klm of same mass.
Whilst you may not stop immediately when hitting the oncoming object, however the force at impact will be greater when 100kph meets 100kph.

Eitherway you are dead!

My question is:
If a plane is on a conveyor...........

lol

[blueline]

Originally Posted by LTDHO

I disagree.

Hiting object at 100kpm will not be as bad as hitting an oncoming object @100klm of same mass.
Whilst you may not stop immediately when hitting the oncoming object, however the force at impact will be greater when 100kph meets 100kph.

Eitherway you are dead!

My question is:
If a plane is on a conveyor...........

lol

^^ agreed, when it comes to the force of when you hit something coming the other way at the same speed, it's whatever your speed plus the speed of the other car. it doesn't matter bout stopping, or getting pushed back, or whatever the outcome is. It's not about being in a bigger vehicle because it transfers more force into the smaller vehicle, it boils down to how much force your vehicle can take.

Originally Posted by XCPWSF

I was wondering about this just before and I can't remember any of my yar 11 physics stuff, but would hitting a solid imovable object at 100km/h be worse than hitting another car head on also travelling at 100km/h?

and in answer to this, hitting another car travelling at 100km/h while you are doing 100km/h is worse than hitting an solid immovable object.

and i also would not want to take part in either situation as well.

[Chopped]

If you roll a ball into a wall it will rebound back a certain distance.

If you roll two balls at each other with equal speed they will still rebound apart at the same distance as if they hit a wall.

So it's that same.

I have a piece of string, how long is it ?

[Brazen]

From a purely physics point of view, hitting an immovable object is the equivalent of hitting an object of the same mass and speed from the opposite direction.

That is why I am critical of ANCAP tests, a five star Ford Fiesta hits the wall at 60kmh - is the equivalent of hitting another Ford Fiesta travelling at 60kmh from the opposite direction. But my question is how many cars on the road weigh the same as the Fiesta? In reality the Fiesta would collide with a lot more heavier cars on the road which throws the test out in real world conditions.

That is why ALL THINGS BEING EQUAL a five star heavier car (like a Falcon) is probably safer in real world conditions than a light 5 star car.

[geckoGT]

Originally Posted by GTP owner

Maggot got it right. Two cars of exactly the same type and mass hitting each other at 100km is NOT equal to a 200km/h collision. If your car weighed substantially less than the opposing vehicle (say you are a barina and they are a truck) and you go backwards as a result of the collision at 100km/h, then, and only then is the force equivalent to a 200km/h collision.
So two equal cars colliding will have exactly the same crumple zones, so will be exactly the same as hitting a brick wall. There will be no reduction in force as a result of their crumple zone giving way unless you weigh more than they do.
This is why it is seen as safer for you to have a heavier car (as in a 4x4) because more of the force is transferred to the smaller car - ie. they go backwards, while you do not completely stop. As an example - you have a landcruiser and they have a barina. They will go backwards at 20km/h, meaning their impact is the equivalent of a 120km/h collision, which is unsurvivable. The cruiser decelerates to 20km/h, meaning the force is of a 80km/h collision, which will probably be fatal.

When you are talking two passenger cars involved in a 100 km/h head on collision, individual vehicle weight have very little to do with it, neither will have a "survivability" advantage. This of course relevant to two passenger vehicles, if you make one a car and the other a B double, that is different.

I assume in your example that both vehicles are traveling at 100, the landcruiser will not decelerate from 100-20, it will stop (quickly). Considering the combined force of the impact is 200 km/h, both vehicles, regardless of mass still sustain a 200 km/h impact. Your example gives the false impression that you are more likely to survive in a landcruiser than a barina. This is a over simplified assumption and does not take into account effectiveness of crumple zones, safety restraints and force transference to occupants. Interestingly, statistically you are more likely to be involved in an accident in a 4wd and when you are you are more likely to be killed. Does not say much for the "safety of 4wd's theory" does it?

Looking at forces involved, the other car at same speed in opposite direction is still worse than stationary object. Although not twice as bad as the speeds involved would suggest due to other factors, but still worse. At least that is what all the research and study I have done on vehicle accident kinematics suggests. The end result is neither would be particularly survivable, in any vehicle.

[geckoGT]

Originally Posted by Brazen

From a purely physics point of view, hitting an immovable object is the equivalent of hitting an object of the same mass and speed from the opposite direction.

That is why I am critical of ANCAP tests, a five star Ford Fiesta hits the wall at 60kmh - is the equivalent of hitting another Ford Fiesta travelling at 60kmh from the opposite direction. But my question is how many cars on the road weigh the same as the Fiesta? In reality the Fiesta would collide with a lot more heavier cars on the road which throws the test out in real world conditions.

That is why ALL THINGS BEING EQUAL a five star heavier car (like a Falcon) is probably safer in real world conditions than a light 5 star car.

The calculation of the 5 star rating is made on passenger injury patterns and passenger cell deformation. If a small car has achieved a 5 star rating and a large car has achieved a 5 star rating, they both demonstrated similar injury patterns and passenger cell deformation when equivalent forces are applied. There is no difference between small car and large car 5 star ratings.

[SLO AU XR8]

Originally Posted by geckoGT

When you are talking two passenger cars involved in a 100 km/h head on collision, individual vehicle weight have very little to do with it, neither will have a "survivability" advantage. This of course relevant to two passenger vehicles, if you make one a car and the other a B double, that is different.

I assume in your example that both vehicles are traveling at 100, the landcruiser will not decelerate from 100-20, it will stop (quickly). Considering the combined force of the impact is 200 km/h, both vehicles, regardless of mass still sustain a 200 km/h impact. Your example gives the false impression that you are more likely to survive in a landcruiser than a barina. This is a over simplified assumption and does not take into account effectiveness of crumple zones, safety restraints and force transference to occupants. Interestingly, statistically you are more likely to be involved in an accident in a 4wd and when you are you are more likely to be killed. Does not say much for the "safety of 4wd's theory" does it?

Looking at forces involved, the other car at same speed in opposite direction is still worse than stationary object. Although not twice as bad as the speeds involved would suggest due to other factors, but still worse. At least that is what all the research and study I have done on vehicle accident kinematics suggests. The end result is neither would be particularly survivable, in any vehicle.

From a Physics point of view, hitting a moving oobject of the same mass at the SAME SPEED is the equivalent of sitting a solid, immovable object. It is only when speed and mass differences occur that the equivalent forces are different, and can change the equivalent speed to be higher or lower.

[Wally]

Originally Posted by XCPWSF

I was wondering about this just before and I can't remember any of my yar 11 physics stuff, but would hitting a solid imovable object at 100km/h be worse than hitting another car head on also travelling at 100km/h?

Kinetic energy increases by the square of the velocity. A car travelling at 100 kph relative to an object has 25% of the kinetic energy compared to travelling at relative 200kph

Cars are made to absorb/convert impact energy by deflecting or compressing over an extended displacement. e.g. by buckling side frame crash boxes. This gives rise to vehicle crush stiffness coefficients. But because the F=ma law still applies the total % absorption depletes by the square of the velocity once again. A crash box might only need 100kN to buckle 100mm, a car doing 100kph is going to have a lot more force than that.

A solid immovable object ideally won't absorb any energy, but your chances are theoretically better hitting it at 100kph than another car head on doing the same speed, by a factor of about two.

[dsyfer]

My guess is this question is about: if you see a car heading towards you on the wrong side of the road and if you had the time to react, would you choose to put your car into a tree or have a head on with the car?

[Brazen]

Originally Posted by geckoGT

The calculation of the 5 star rating is made on passenger injury patterns and passenger cell deformation. If a small car has achieved a 5 star rating and a large car has achieved a 5 star rating, they both demonstrated similar injury patterns and passenger cell deformation when equivalent forces are applied. There is no difference between small car and large car 5 star ratings.

Hitting an immovable object is the equivalent of hitting a car with the same mass at the same speed from the opposite direction, how many cars on the road are the same mass as a 1000kg Fiesta?

The point I was making is that a Fiesta gets the 5 star rating in a test which is the equivalent of hitting another Fiesta head on (ie same mass), the Fiesta isnt tested against hitting an object of greater mass (ie against a Falcon or a Landcruiser) - This has been demonstrated is numerous tests including a 4 star Audi SUV (greater mass) hitting a 5 star Smart car (smaller mass), the results were minor injuries to the Audi driver with life-threatening injuries to the Smart driver. The Smart gets its 5 star rating hitting the equivalent of another Smart at the same speed, not against hitting the average vehicle on the road.

The Ancap tests are good for comparing cars which are hitting trees or solid walls, they are not good seeing what the results would be hitting other cars where differences in mass come into play.

[Auslandau]

I would say that 2 objects exactly the same weight, size etc hitting at 200 would be twice that as a solid object at 100.

The impact coming at you at is travelling at 100 km/h also (overall speed=200kms/h) and once hit isn't going go to absorb much if anything .....

I'll supply the cars and a helmet! Just need someone to steer. For $100 anyone?? ..... would make good you tube!



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[SLO AU XR8]

Originally Posted by auslandau

I would say that 2 objects exactly the same weight, size etc hitting at 200 would be twice that as a solid object at 100.

The impact coming at you at is travelling at 100 km/h also (overall speed=200kms/h) and once hit isn't going go to absorb much if anything .....

I'll supply the cars and a helmet! Just need someone to steer. For $100 anyone?? ..... would make good you tube!

Yes, But that is incorrect. At impact, it is the equivalent of of hitting a stationary object on both sides. both cars will be hitting at the same speed and cancelling out the fact that the other is moving.

[Auslandau]

Originally Posted by SLO AU XR8

Yes, But that is incorrect. At impact, it is the equivalent of of hitting a stationary object on both sides. both cars will be hitting at the same speed and cancelling out the fact that the other is moving.

..... but what you are saying is that there is no difference to hitting a stationary car and one coming at you at 100km/h?



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[Wally]

Originally Posted by SLO AU XR8

Yes, But that is incorrect. At impact, it is the equivalent of of hitting a stationary object on both sides. both cars will be hitting at the same speed and cancelling out the fact that the other is moving.

If someone threw at a 100kph ball at your baseball bat and you didn't swing it would be a bunt, if you swung the bat with equal force you might hit it out of the park.

[4Vman]

Originally Posted by SLO AU XR8

From a Physics point of view, hitting a moving oobject of the same mass at the SAME SPEED is the equivalent of sitting a solid, immovable object. It is only when speed and mass differences occur that the equivalent forces are different, and can change the equivalent speed to be higher or lower.

Correct, equal and opposing forces will cancel each other out, the variables are weight, angle of collision and speed of the 2 objects, 2 cars of equal weight (inertia) hitting squarely head at 100kpm each will have the effect of hitting a padded (compensate for crumple of second vehicle) brick wall at 200kph...

[Auslandau]

Originally Posted by Wally

If someone threw at a 100kph ball at your baseball bat and you didn't swing it would be a bunt, if you swung the bat with equal force you might hit it out of the park.

That is a good way to put it ...... fast bowlers get wacked out the oval constantly ... faster the ball the further it goes with less effort from the batsman.



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[RedHotGT]

From a Physics Point of view - the solid object at 100km/h would be less impact and force than 2 cars of equal size/weight/speed hitting head on at 100km/h.

Inertia is what the big factor is....
one stationary object, and one travelling at speed of 100km/h
vs
two identical objects travelling towards each other at 100km/h

you can have all the crumple zones / airbags / safety features that you like....
but at the end of the day - the PHYSICS answer is that the 2 cars head on will be worse than hitting a solid object at 100km/h.

My old man wrote the book on Yr11 & Yr12 Physics (literally - http://www.seekbooks.com.au/book/Phy...0701637811.htm)
It is used in 90% of schools in Australia... He knows his stuff....
I've chatted to him, and he also agrees with the above...

[flappist]

This is a lot more complex than it looks.

Assumptions:

1) The cars are absolutly identical and symmetric (as they will be hitting each other with the opposite sides).
2) The solid object is immovable.

If these are both the case then the impact theoretically would be exactly the same.
In the case of the 2 cars each would crumple at exactly the same rate thereby presenting what would be a flat immovable object to the other.

If there was a difference in structure between the two vehicles then the result could be anything from total annihiliation to "did you here something then, sounded like bump".

But is all cases some if not all of the people will not have a lot of fun....

[RedHotGT]

Originally Posted by flappist

This is a lot more complex than it looks.

If these are both the case then the impact theoretically would be exactly the same.

Theoretically they are not exactly the same at all....

Maybe a bit more detailed question from the start would stop arguing...
The question should be based on if YOU were driving the vehicle, what would be worse for YOU...

If you hit an immovable object at 100km/h, the force/inertia/momentum of you inside the vehicle experience G forces and negative G forces (as the car would be pushed back from the object once it has hit it)...

You would experience MORE G force and negative G force from 2 x objects that has the same force/inertia/momentum when they impact each other(instead of just one with the previous example)...

But, the bottom line answer to the question is that I would rather not be involved in either scenario - and continue to order my drink at the bar thank you sir....

[flappist]

Originally Posted by loftie

Theoretically they are not exactly the same at all....

Maybe a bit more detailed question from the start would stop arguing...
The question should be based on if YOU were driving the vehicle, what would be worse for YOU...

If you hit an immovable object at 100km/h, the force/inertia/momentum of you inside the vehicle experience G forces and negative G forces (as the car would be pushed back from the object once it has hit it)...

You would experience MORE G force and negative G force from 2 x objects that has the same force/inertia/momentum when they impact each other(instead of just one with the previous example)...

But, the bottom line answer to the question is that I would rather not be involved in either scenario - and continue to order my drink at the bar thank you sir....

Exactly wrong loftie.

If one is stationary and immovable it must absorb the energy of the other object while that object collapses. The point of collision is fixed.
If both objects are identical then each absorbs the same amount of energy at the same rate and the point of collision is still fixed..

If you roll a perfect rubber ball at 10m/s into a wall it bounces off at 10m/s
If you roll the same rubber ball at 10m/s into another rubber ball at 10 m/s the BOTH bounce back at 10 m/s.

In immovable object MUST be exactly equivalent to an identical object travelling in the opposite direction OR ELSE IT WOULD MOVE.....

Ask your dad again, giving him all the details.......

[4Vman]

Oh dear...

[MAD]

Originally Posted by flappist

In immovable object MUST be exactly equivalent to an identical object travelling in the opposite direction OR ELSE IT WOULD MOVE.....

+1

The simplest way to think about it is a force balance.

1. For the car to stop when it hits the wall, the wall must present enough opposing force to cancel the force the car is carrying. Otherwise the wall would not be immovable.

2. Two steel blocks of the same weight/shape/etc are propelled at each other at the same speed they are both carrying the same speed so when they collide, each block is presented with the exact same opposing force from the other block, which will cancel each blocks movement.