126SEC Easter Weekend Fatalities - Page 3 - Mercedes-Benz Forum

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post #21 of 36 (permalink) Old 05-14-2007, 08:19 PM
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I'm surprised the Impala held up better than the SEC...but then again...the Impala is more modern thus much safer.
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post #22 of 36 (permalink) Old 05-15-2007, 03:47 PM
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Originally Posted by chinny4290
I'm surprised the Impala held up better than the SEC...but then again...the Impala is more modern thus much safer.
I doubt it.

From the look of the accident physics dictate that the SEC received the hardest hit. Considerably harder.

These women were cruising along on the grass median at ~ 25 - 30 mph, while along comes a speeding Impala in the outside lane, he brakes when the SEC suddenly swerves in front of him but it is too late. The Impala, shouldering the most inertial force slams into the Mercedes and the Mercedes absorbs the greatest amount of energy.

I'm guessing the driver of the Mercedes had some kind of seizure of sorts, while her friend was trying to bring the car to a stop. This would seem to match the reason as to why there were no drugs or alcohol involved and the fact that the driver was elderly.
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post #23 of 36 (permalink) Old 05-15-2007, 04:49 PM
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Interesting but sad demonstration of crash dynamics at work. Speaking of physics, you have to look at this in the proper reference. This collision is a closed system. Each car recieved the same amount of force during the initial collision. No car was hit harder than the other. What is different is how that energy was dissipated in the system during the collision. Each car buckled during the impact and turned kinetic energy into deformed metal and heat. Taking away energy and slowing the impact forces in the car and giving the occupants a better chance of survival is the game. Even though the cars did a good job at protecting the cabin the SEC probably experienced greater decelleration forces against the heavier car. This was beyond the edge of survivability for a pair of +60 year old women.
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post #24 of 36 (permalink) Old 05-15-2007, 08:39 PM
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Originally Posted by AzimuthAviation
Interesting but sad demonstration of crash dynamics at work. Speaking of physics, you have to look at this in the proper reference. This collision is a closed system. Each car recieved the same amount of force during the initial collision. No car was hit harder than the other. What is different is how that energy was dissipated in the system during the collision. Each car buckled during the impact and turned kinetic energy into deformed metal and heat. Taking away energy and slowing the impact forces in the car and giving the occupants a better chance of survival is the game. Even though the cars did a good job at protecting the cabin the SEC probably experienced greater decelleration forces against the heavier car. This was beyond the edge of survivability for a pair of +60 year old women.
What's to understand?

If the Impala was traveling at a greater speed than the SEC then the bulk of the combined 100 mph impact's energy is transferred to the SEC.
Simply, F = MA, the second law of Newtonian physics.

All the energy of the force from the Impala overpowering the SEC and causing the SEC to absorb the most energy from the wreck, while the women experience greater deceleration forces, indeed, not just from the lack of energy absorption but because of the greater force.

If I am incorrect, please explain why.
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post #25 of 36 (permalink) Old 05-16-2007, 06:22 AM
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Originally Posted by DslBnz
What's to understand?

If the Impala was traveling at a greater speed than the SEC then the bulk of the combined 100 mph impact's energy is transferred to the SEC.
Simply, F = MA, the second law of Newtonian physics.

All the energy of the force from the Impala overpowering the SEC and causing the SEC to absorb the most energy from the wreck, while the women experience greater deceleration forces, indeed, not just from the lack of energy absorption but because of the greater force.

If I am incorrect, please explain why.

hmmm wished i'd pay more attention in physics class! but AzimuthAviation's explanation sounds right too...but i suppose if a bowling ball and a ping pong ball was on a collision travelling at the same speed the ping pong would be toast...but is the impala that much heavier than the SEC? how bout conservation of momentum? does that have anything to do with anything?
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post #26 of 36 (permalink) Old 05-16-2007, 01:26 PM
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Originally Posted by picklesam
hmmm wished i'd pay more attention in physics class! but AzimuthAviation's explanation sounds right too...but i suppose if a bowling ball and a ping pong ball was on a collision travelling at the same speed the ping pong would be toast...but is the impala that much heavier than the SEC? how bout conservation of momentum? does that have anything to do with anything?
This whole thing is ridiculous.

Forget weight for a moment. Weight is important, but not the sole determinant. Weight and inertia are. The object shouldering the most inertia involved in the impact will suffer only the resistance of the object it comes into contact with.

Think of it this way. If you were to interpret the speeds of impact as the same, 30 mph, it would be like having a 9K lb truck hit the 4K lb SEC at a combined speed of 60 mph with each vehicle at 30 mph. The damage to the SEC would be the same.

FWIW, the SEC is similar in weight to the Impala.
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post #27 of 36 (permalink) Old 05-17-2007, 02:06 AM
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Originally Posted by DslBnz
What's to understand?

If the Impala was traveling at a greater speed than the SEC then the bulk of the combined 100 mph impact's energy is transferred to the SEC.
Simply, F = MA, the second law of Newtonian physics.

All the energy of the force from the Impala overpowering the SEC and causing the SEC to absorb the most energy from the wreck, while the women experience greater deceleration forces, indeed, not just from the lack of energy absorption but because of the greater force.

If I am incorrect, please explain why.
No problem! It is a closed system with a single point of reference at initial impact. The design of the cars will distribute the energy over time. In your first sentence it would make sense then that if the SEC was absolutely stationary, then the only damage would have been to the Benz! A car going 100mph into a stationary one, and two cars hitting with each going 50mph is the same in a closed system. The net result is a 100mph collision. A feather and a bowling ball each experience the same amount of force during a collision. It's very obvious though that the object with lessor mass will experience a greater change in it's energy state during a collision (same force but less mass equals a greater acceleration) but the systems energy remains the same. You're correct in the basics of F=ma. The initial force on the bumpers was the same. You're now taking the kinetic energy (1/2 mv^2) of the system and trying to turn it into a result of zero. Do the math and a litte less mass is going to have to slow down much faster expending greater amounts of energy using great forces in the cabin of that car after the frame has met resistance from further distortion. Again, the crumple of the car frames is trying to take that energy and turn it into heat.

Last edited by AzimuthAviation; 05-17-2007 at 02:14 AM.
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post #28 of 36 (permalink) Old 05-17-2007, 03:07 PM
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Originally Posted by AzimuthAviation
No problem! It is a closed system with a single point of reference at initial impact. The design of the cars will distribute the energy over time. In your first sentence it would make sense then that if the SEC was absolutely stationary, then the only damage would have been to the Benz! A car going 100mph into a stationary one, and two cars hitting with each going 50mph is the same in a closed system. The net result is a 100mph collision. A feather and a bowling ball each experience the same amount of force during a collision. It's very obvious though that the object with lessor mass will experience a greater change in it's energy state during a collision (same force but less mass equals a greater acceleration) but the systems energy remains the same. You're correct in the basics of F=ma. The initial force on the bumpers was the same. You're now taking the kinetic energy (1/2 mv^2) of the system and trying to turn it into a result of zero. Do the math and a little less mass is going to have to slow down much faster expending greater amounts of energy using great forces in the cabin of that car after the frame has met resistance from further distortion. Again, the crumple of the car frames is trying to take that energy and turn it into heat.
I assume weights to be the same.

Generalizing:
A car traveling at 70 mph is producing more kinetic energy than one traveling 30 mph. The two energies together produce a force upon impact. The 70 mph vehicle of equal mass will cancel out the 30 mph vehicle's speed and force it to a stop (there's your stationary) or further back (which could take some energy with it), but considering the wheels were probably locked, not much. The combined impact, the total force, depends on which vehicle was the slowest moving. The one with the greatest kinetic energy will fare better than the one with the least.

If I slam my head into yours, YOU will be the one with the headache, not ME.
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post #29 of 36 (permalink) Old 05-17-2007, 08:42 PM
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geeish, i'm really confused now..so aviation is saying if object A colliding into a stationary object B at 60mph, the wreck will be the same as A and B colliding at 30mph? and DslBnz is saying B will be worst off in the first scenario?
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post #30 of 36 (permalink) Old 05-17-2007, 09:00 PM
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Originally Posted by picklesam
geeish, i'm really confused now..so aviation is saying if object A colliding into a stationary object B at 60mph, the wreck will be the same as A and B colliding at 30mph? and DslBnz is saying B will be worst off in the first scenario?
That's what I'm saying.

The total energy of the wreck will be the same in both, but depending on the scenario the overall outcome will vary.

Remember that video many of us members saw of the W126 slamming into that pack of cars at 70 mph? That's what happens. That energy was absorbed by that pack of cars, not by the W126. The only energy the W126 absorbed was from the resistance the stationary economy cars provided (which wasn't much).

It would've looked a bit different had the Fiat slammed into the W126 at 70 mph.
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