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| Thread ID: 89795 | 2008-05-12 10:07:00 | Speeds and crashes | qazwsxokmijn (102) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 668609 | 2008-05-12 11:28:00 | Beware! Some petty official is going to pounce for not stating that you should not try this at home. There is probably a department for the purpose with awesome powers to hive off to conferences worldwide at the drop of a hat. Remember we are talking fearsome iMpacts here. |
R2x1 (4628) | ||
| 668610 | 2008-05-12 12:05:00 | It is really defendant on the mass of the cars . If a heavy car hits a lighter car, it is going to exert much more force, therefore doing more damage even though it made contact at the same velocity . Hitting a car head on is going to create more damage (but driver will feel less impact) than rear ending simply because cars are now designed that way . I think this is called shock or impact zone or something like that . If two cars of same mass and traveling at same velocity hit each other head on then the total forces double I think . The momentum should be conserved . |
Deathwish (143) | ||
| 668611 | 2008-05-12 12:18:00 | cars today will have a crumple zone so that it absorbs impact force if you crash or have a head on collision | williamF (115) | ||
| 668612 | 2008-05-12 12:52:00 | Wrong on the second count. A stationary car is still going to move with the impact, dramatically lessening the force of the impact. Two cars meeting at 100kph a piece would be like a car hitting a thick concrete barrier at 200kph. Well maybe not a concrete barrier. But a more solid object than a stationary car. nope. assuming identical cars (so crumple zones and mass are the same) it doesn't matter what one or the other is doing relative to an observer, only what they are doing relative to each other. if the total energy is xxxxxJoules then that much energy has to be absorbed reguardless of velocity the stationary car moving backwards is just conservation of momentum. when two cars have a head on they both have forces pushing them backwards. provided the total momentum is the same, the absolute velocities and even the relative velocities have no effect it's all conservation of momentum, which comes from conservation of energy. It is really defendant on the mass of the cars. If a heavy car hits a lighter car, it is going to exert much more force, therefore doing more damage even though it made contact at the same velocity. Hitting a car head on is going to create more damage (but driver will feel less impact) than rear ending simply because cars are now designed that way. I think this is called shock or impact zone or something like that. If two cars of same mass and traveling at same velocity hit each other head on then the total forces double I think. The momentum should be conserved. force is mass times acceleration so if the car crumples a bit, absorbing energy doing so, there can be less force on the occupants the weights of the car have nothing to do with it if the total momentum is the same. all that means is that a 2tonne car travelling at 50kph has the same energy/momentum as a 1 tonne car doing 100kph. provided they both absorb energy crumple at the same rate and to the same degree, the "damage" will be equal conservation of momentum (and relative motion) is the whole idea behind the original post cars today will have a crumple zone so that it absorbs impact force if you crash or have a head on collision tail end too, and sides to a degree plus all the airbags etc etc and before someone says it, no, having a solid brick of a car does NOT help. it means greater forces acting on you, and more damage to the other car if it's soft. if the other car is a brick, well you're both going to get hurt. may not be a broken bone, but when your heart rips from the aorta you've got about 3 minutes to live. loose spleens/kidneys aren't so bad; a least they can be diagnosed and operated on in the few hours before you bleed internally to death moral of the story: KEEP LEFT meanwhile us bikers just hope we land somewhere soft... not so bad with cars as you sail over them, but 4wds and vans mean you go through a window/pillar.... bu tof course ltnz insists on putting as many lethal cheesecutter roadside barriers in as they can, rather than safer (and more effective) continous concrete barriers hat actually stop trucks/cars crossing centrelines into oncoming traffic. they even flout the manufacturere specs of 3m clearance either side; those bariers are not safe |
motorbyclist (188) | ||
| 668613 | 2008-05-12 21:01:00 | Fine lol. :lol: :p | wratterus (105) | ||
| 668614 | 2008-05-13 03:11:00 | The energy depends on the square of the speed. Twice the speed gives four times the kinetic energy. This is one of the reasons for speed limits. The rear end shunt would cause exactly the same amount of damage as the stationary 20 km/h collision. After the collision, more damage will occur if one or both drivers loses what control they had before the collision, and hit other objects. ;) The higher speed question is a little bit trickier; I think the stationary vs 200 km/h crash would actually involve twice the energy. {assuming equal mass vehicles, the energies are 2([1/2]mv^2) versus [1/2]m(2v^2) , which comes out to mv^2 vs 2mv^2. } Terry will correct me if I'm wrong. ;) |
Graham L (2) | ||
| 668615 | 2008-05-13 05:41:00 | I'm sure Graham is right, additionally with the 200km/h collision into an immovable object, that extra energy (2mv²), goes into trashing just the one car, rather than 1/2mv² trashing each car. I would also prefer to be rear ended at 20km/h when I'm sitting stationary, in neutral, and with foot and hand brakes off :) But on the other hand if you are stationary at traffic lights and/or behind other vehicles then it only makes sense to be in neutral with the hand brake hard on. Those who sit on the clutch at lights....think about it.:horrified |
Terry Porritt (14) | ||
| 668616 | 2008-05-14 06:32:00 | Its because the parked car has no inertia of its own to multiply the impact of being hit by something else. Umm..........The parked car has plenty of inertia, but no momentum! And this one: Then again maybe the cars going 100 and 120 would encounter less damage seeing as a stationary car is harder to put into a state of motion than accelerating an already moving car (when it gets rear ended) Will be little different because the target vehicle (or victim) still has to accelerate by 20km/h over virtually the same distance as the stationary car. What happens after the intial impact is another matter of course, the speeding cars could come unstuck big-time, especially if driven by Yanks and cruising down the freeway. Cheers Billy 8-{) |
Billy T (70) | ||
| 668617 | 2008-05-14 06:49:00 | Those who sit on the clutch at lights....think about it.:horrified What about it? |
Metla (12) | ||
| 668618 | 2008-05-14 07:45:00 | What about it? If you get rear ended at traffic lights when sitting on the clutch, the probability is you are going to be shunted into the traffic stream going by, or, if there is a stationary car in front you will rear end that also. |
Terry Porritt (14) | ||
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