10-22-2011, 12:28 PM | #15 |
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Visualize the problem this way. Imagine 2 exactly the same vehicle hitting perfectly head-on. The middle plane where the 2 cars meet will be the symmetry plane. Then all the mass of each car from the symmetry plane all the way to the back of each vehicle will have a velocity of 120mph at impact. The crushing of the each vehicle will start at the symmetry plane and progress toward the back of each vehicle. This happens because the mass at the front of the each car slowed down first and the back of each car keeps on coming. The progression of the crushing is slowing each car until all the mass of each vehicle is completely slowed down and rebound. Neither car's front end will pass thru this symmetry plane. Hence it's equivalent to each car is hitting a rigid/fixed plane at 120mph. All cars can only be designed for survivable accidents. Most will have their front end completely crushed at about 30-40mph into a rigid/stone wall. When you double or triple the speed, your kinetic energy is increased by a factor of 4 to 9. There is not much hope unless you have a full hi-strength steel cage or a tank. Even if you can design a structure to withstand that kind of crash, I am not so sure the occupant can survive from the head deceleration alone.
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10-22-2011, 12:34 PM | #16 | |
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We do this all the time with car crash simulation. It's also a lot cheaper with Finite Element method than actual crash tests. Auto makers worldwide have been using a product called ls-dyna (I do this for a living) to do most if not all of their crash work. Actual crash tests are only needed at the end of the design cycle to prove it to NHTSA.
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10-22-2011, 12:42 PM | #17 | |
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Quote:
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__________________ Originally Posted by FbodFather My sister's dentist's brother's cousin's housekeeper's dog-breeder's nephew sells coffee filters to the company that provides coffee to General Motors...... ........and HE WOULD KNOW!!!!__________________ Camaro Fest sub-forum |
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10-22-2011, 03:27 PM | #18 |
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Kind of reminds me of the joke, "what's the last thing that goes through a bugs mind when it hits the windshield?"
This is why crash testing is done with a gazzilion ton steel wall. It is intended to simulate two cars of exactly the same mass hitting each other head on at exactly the same speed. So a 30 mph government crash test simulates two identical cars hitting each other head on at 30 mph for the unbelted test. An unbelted 30 mph frontal crash is a pretty scary thing to watch in real time and in person, btw.
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10-23-2011, 12:29 AM | #19 |
Turbine Cowboy
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watched the clip again and at the begining he does state "2 cars hitting head on while both traveling at 120mph" so i would guess that the total force would actually be 240mph
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10-23-2011, 04:16 AM | #20 |
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10-23-2011, 04:48 AM | #21 | |
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Erhm.... "The closing speed between two vehicles".... I think that is where you're taking the wrong decision. Indeed, if two vehicles move towars each other, their closing speed will be the sum of both speeds. Both vehicles also have crumple zones designed to absorb the forces of impact. Take out one vehicle and replace it by a solid, non deformable object, like a concrete wall... and you're looking at a totally different perspective, since the only thing having crumple zones is the vehicle that moves, which will inevitably magnify the effect of the impact. |
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10-23-2011, 09:56 AM | #22 | |
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I used a line very similar to that in a post few months after I joined, I've had it as a signature for about 4 years now.
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__________________ Originally Posted by FbodFather My sister's dentist's brother's cousin's housekeeper's dog-breeder's nephew sells coffee filters to the company that provides coffee to General Motors...... ........and HE WOULD KNOW!!!!__________________ Camaro Fest sub-forum |
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10-23-2011, 10:12 AM | #23 |
OKCamaros
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Dammm!! that was crazy!!
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10-23-2011, 10:21 AM | #24 |
Retarded One-Legged Owl
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At those speeds, a crumple zone isn't going to help much...
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10-23-2011, 11:33 AM | #25 |
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Ouch...
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10-23-2011, 01:39 PM | #26 | |
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Quote:
Either way, it's pretty simple.... crash into a car at 120mph (be it both moving or not) and you'll not walk away because of the immense G forces at work during the deceleration... (and that is, I believe where the "crumple zones" actually start doing their work, by dividing the energy during the transition from moving to standing object). |
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10-23-2011, 03:50 PM | #27 |
Retarded One-Legged Owl
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E = mc² has nothing to do with conservation of energy. It's just a concept that the mass of an object is a measure of its energy content. The "c" in that equation is merely a constant to convert between the two.
The equation you are thinking of is for kinetic energy, which is E = 0.5mv² In a closed system, the laws of conservation of energy dictate that the amount of energy in the system is constant. The problem with trying to apply this principle to vehicle collisions has to do with the elasticity of the collision and how the energy in the collision does not remain solely as potential or kinetic energy. Crumple zones in a car don't really "absorb" energy. They just lengthen the time of impact. The longer the impact takes, the less G-forces encountered by the occupant. But, like I said, at those speeds, the crumple zones won't really do much...
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10-23-2011, 11:23 PM | #28 | |
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You are right that they slow down the crash event, and that is how they save lives. But how do they slow the crash down? They slow it down by ... absorbing energy. Like a spring. But reverse the efficiency so that instead of wasting a couple percent of the energy as heat & sound while storing the vast majority as potential energy (which then gets released as kinetic energy), they convert the vast majority of the into heat and sound with a minimum being stored & released
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__________________ Originally Posted by FbodFather My sister's dentist's brother's cousin's housekeeper's dog-breeder's nephew sells coffee filters to the company that provides coffee to General Motors...... ........and HE WOULD KNOW!!!!__________________ Camaro Fest sub-forum |
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