In the situation involving two vehicles the crumple zones and the airbags are working to protect the occupants of _that vehicle only_. In that sense it is no different than the situation involving one vehicle and a wall. In the single vehilce collision, the air bags and crumple zones are still only working to protect the occupants of one vehicle.

Also, you have the Mass of one vehicle X the Velocity of one vehicle not the Energy of the vehicle. The Energy of the vehicle is = Mass X Velocity.

In the case of two vehicles hitting each other you have twice the energy, but you also have twice the distance over which to dissipate it (2 crumple zones) and the force, in the end, is the same.

The problem is you have no point of reference. When was the last time you saw what happened to a car when it rammed straight into a solid wall that did not collapse? Probably never. I know I have never seen it in real life. In all of the crash videos, however, the damage is astonishing.

Look at it another way:
A car traveling 60MPH hits a wall. The moment the front bumper hits the wall it stops moving. A force is being exerted by that wall to stop the car without letting it move beyond the point that the bumper contacted the wall.

In the case of two cars hitting each other, the bumper of the other car is acting exactly like that wall. It is exerting a force on the other car to stop it from moving without moving itself. If that is the case, then distance over which to bleed off the energy of the accident is the same whether it a one car or two car accident.

-Don

 

Umm...not exactly like the wall as this (two cards) has forward momentum and if the mass is great enough it will have more impact then just hitting a wall.

 

Ah, see there? I didn't check back on what happened, and I was WRONG. But, since I didn't know the people in the motorhome in any way, I am sure it was their fault...

For the record, I completely agree with you. Stupid is as stupid does, no? :P
Uh, the difference being they hit a vehicle more than twice their GVWR??? Not a point most people have touched on in this thread(and quite the physics lesson it is for me!) but the mass of the two vehicles involved in Tundras case is quite different. That and the type/design of the other vehicle is why there were no fatalities in the motorhome in Tundra's accident.

On a smaller note, you mention the other driver as "the innocent person in the oncoming lane". What if that person was or is responsible for the next Hitler? What then? If your answer is "we don't/can't know that" then thank you, you have proved my point.

Thank you, and I will, they deserve at least that much.

 

To all the physics majors(and wannabes) -

I find this very interesting. I know its a little OT from the intent of the thread, but nonetheless its obvious there are WIDELY deiffering opinions on how this whole crashing thing works. I have read all the replies thus far and find myself agreeing with both sides at times!

I have a question though. If an object at rest tends to stay at rest, then if a vehicle hits another head on at 60 mph, wouldn't the target vehicle(whichever, lets call it vehicle two) not move much follwoing the impact - having to not only absorb the force of going 60 to zero but also being hit at 60 mph?

I am such an amateur its sad, but it is interesting!

 

Ok I give up. I am going to go to bed and get some sleep so I can actually get up for work in the morning.

Before I leave, however, let me make one final attempt:

When a single car hits a wall, the wall exerts a force on the car equal and opposite to the force exerted by the car on the wall. If the force exerted by the car were greater, the wall would move. If the force exerted by the wall were greater, the car would accelerate backwards.

In order for the car to have a 0 velocity after the impact, the wall and car must exert equal and opposite forces on each other for the duration of the deceleration.

The force exerted by the car on the wall can be calculated by F=MA. The force is equal to the mass of the car multipled by the acceleration (or in this case deceleration) of the car. The deceleration of the car takes place over the distance of the crumple zone.

This means we know the force that the wall must exert on the car to bring it to a stop. As a result, we also know the force exerted by the car on the wall. They are equal and opposite.

Now if two cars hit each other, and each one comes to rest over the same distance (the crumple zone) as when it hits a wall, then we know the force is the same as if it hit a wall (It has to be since the car distance over which it came to rest is the same and the initial velocity was the same).

Since we know the force of one car, and the cars are at rest after the accident, then we know the force of the other car was equal and opposite. In other words, car A exerts a force of X on car B and car B exerts a force of -X on car A. If this were not true, the cars would not be at rest after the accident.

In the case of the car hitting the wall, the car exerts a force of X on the wall, and the wall exerts a force of -X on the car.

Whether it is a car exerting a force on another car, or a wall exerting a force on a car, the force it self is still the same magnitude.


x = v0t + .5 at^2

Thus a = 2(x - v0t)/t^2

Where x is the distance over which the deceleration takes place. In this case it is the length of the crumple zone of the car. v is the velocity and is 60 MPH in every example.

In order for both cars to be at rest after the accident, the forces must be equal and opposite. Thus: F0 = -F1 or M0A0 = -M1A1 where F0 is the force exerted by the first car and F1 is the force exerted by the second car.

If a car hits a wall, and comes to rest, then once again we must have equal and opposite forces. The force exerted by the wall must equal the force exerted by the car. F0 = -F1 or M0A0 = -M1A1.

The force required to stop the car is:
F = M * (2(x - v0t)/t^2)

It does not matter whether it is another car exerting that force, or a wall exerting it, it is the same in either case.

It is late and I am beginning to ramble. Night folks.

-Don

 

Clearly the only way to resolve this is to take our trucks out and ram them into each other head on and then run some other ones into a wall and see what happens.

-Don

 

Each vehicle only has to absorb the force of itself going from 60 to 0. The other vehicle is responsible for absorbing the other 60 to 0 deceleration.

In the case of hitting a wall, the single vehicle is still responsible for absorbing the force of going from 60 to 0.

-Don

 

People like YOU are the exact reason that I didn't go into engineering. I never said I knew it all, you did.

At least I may be only flogging my ignorance. You apparently are home flogging your:

 

Ya might apply for a refund for that education.

Reminds me of the arguments my Grandmother used
to make about the truckers that hauled a$$ through our
small town at the bottom of a big mountain. "I sure am
glad that truck wasn't carrying a ton of STEEL, but rather
a ton of FEATHERS"

F=MA for each instance, so there is no way to INCREASE
("greater" in your words) the total available force or energy.

/e sits back to watch more mental masturbation ...

PS... for all you that don't believe this .. I have a Perpetual Motion
device on E-Bay that you can purchase for $100.00 <grin>

PPS... This discussion proves the law of entropy ... It's only
devolving ...

 

If you look at the two vehicles the damage explains:

The three elements of the collision. First contact= no force at this point. Maxium engagement= force is at it's greatest. Motion has stopped the vehicles, however they still move in relation to the road.

Then you have separation which = departure angles. This collision is a partial head on. The vehicles hit in a eccentric manor. Outside center of mass. Centered/eccentric hit. You can see that the van and lightning had rotation from the separation point. After all of the energy is used up they come to a final resting point.

Now to get the speed at impact you have to do a combined speed momentum formula. You use what ever knows you have at the scene to find the unknow. You put these knows into the combined speed formula.

You can also get speed from crush damage. There are a few other formulas also. It really depends on what the vehicles leave as evidence before and after impact. Skid marks, know speed of one vehicle. Weight of both vehicles, etc, etc.


Herb

 

Hey that's why I am a chemist, not a physicist
Entropy is always increasing btw...don't know about "devolving"

 

hEY GEORGIA... I use to travel 316 all the time on my commute back and forth to UGA.. I know how dangerous it is.. I think the main reason that road is so dangerous is b/c of the students rushing to make class and wanting to hurry home..I've noticed a lot of accidents on 316 occur from students on cell phones, not paying attention..Gwinnett is notorious for a lot of younger "immature" people with high performance 400hp+ vehicles..Anything from vettes,porshes, and vipers you see them a lot.. Therefore a lot of racing and high speed driving goes on in that area.. Gwinnett seems to also be the high crime capitol of Ga now for some odd reason..Very decent area but it seems to be going down.. It's just dangerous anywhere you go now guys..In this day in time it's just better to know deep in your heart and spirit where you're going in the afterlife...

Take care and be careful guys!

 

WOW.. you guys have taken the "sad day" post and turned into a physics equation...

Again... My prayers go out to the family.. Despite how the accident happened, no one is perfect thats why prayer is for everyone...

When i'm read about or see tragedies like these it makes me think it could have been me plent of times..

 

Gang:

In the simplified, generalized world of two IDENTICAL, deformable masses (coefficient of restitution near zero) with identical speed hitting EXACTLY head-on, the effect is the same as one of the masses hitting an "infinitely hard" flat wall of "infinite mass" at the same speed as the two-mass crash.

Two silver Lightnings hitting head-on, each moving at 60 MPH, is for all practical purposes, the same as one silver Lightninng hitting a big-azzed wall of granite at 60 MPH, head-on.

This was the original problem discussed, and this is absolutely true. It's not a theory. It's a BASIC law of the universe.

As soon as you complicate the issue with offset crashes, striking objects other than the infinite flat wall, and the million other complications inserted in this discussion, the analysis shifts a few percent one direction or another due to the introduced esoterica.

But to restate the original "Grandpa-told-me-at-the-local-tavern" issue, where the question is:

Two cars hitting head-on, both moving at 60 MPH, is equal to one car hitting a brick wall at...

A: 60 MPH

B: 120 MPH

The answer is most definitely "A" and not ANYWHERE in the vicinity of "B" (about 60 MPH off, to be exact).

If you want to live in a universe where the answer is "120 MPH", hot water in the ice cube tray freezes faster, trucks with tailgates down are more aerodynamic, and baseballs can rise on their way to the plate, that's your funeral, I suppose.

Fractaldragon:

I'd be VERY interested to know what university's school of science is allegedly going to give you a PhD ("piled higher and deeper") with your obvious complete ignorange of the basic laws of the universe, and your further closed-minded attitude toward learning. Somewhere in the Carribean or possibly by correspondence, I would guess.

 

Can you braniacs take your argument to a Physics forum. Maybe they will be interested in your discussion, but your arguments back and forth were old when they first started. This post was about an unfortunate accident that happened, not a Physics Science class.

My prayers go out to all the families and friends who were affected by this unfortunate accident.