R turbo on the autobahn
Discussion
domster said:
derestrictor said:
Dom, where the f@ck is the beetle?
Doing an extremely safe 0mph!
Rendezvousing with Herr F this wochenende, so will make enquiries
F@ck that for a game of soldiers, my badger sluecing copain: I was supposed to be hop gathering last night - tomorrow or the Salford 7 yomp sarf.
'k?
Decanter said:
200mph club so vigorously.
you seem to have some deep seated psycological problem with that number based, i suspect, on what YOU feel is too fast for you, so in true socialist style no one else should be allowed.
lets call it 26.7 furlongs per minute. there that doesnt sound so fast now. really 26.7 fpm can be safer than 70mph - its totally dependant on conditions, the car, the driver. whats your problem with that statement?
On August 17, 1896 110 years to the day, Bridget Driscoll became the first road fatality in the world. She was hit by a car with a max speed of 4mph, witnesses described her at being hit by a car travelling at "a reckless pace". It turned out that the 'dangerous lunatic' had modified the belt drive to increase the top speed to 4.5mph
Get some perspective, get a life and please stop being such a socialist dullard
Edited by francisb on Thursday 17th August 17:44
Decanter said:
" defending what simply amounts to using excessive speed on an autobahn"
How can excessive speed occur on a road with no limits?
By rationale, excessive implies that there is a limit.
What do you consider excessive speed in that environment then?
Let me remind you of the factors in case you've chosen to ignore them:
Unlimited Autobahn
200mph plus designed German Sports/Supercar
Hugely experienced driver used to 200mph driving in various machines with intimate knowledge of road/cambers/car etc.
At night in clear, calm, dry conditions with full beam headlights designed for such driving.
No other traffic.
Sorry, can't see your point, but carry on anyway.
tony.t said:
You can't argue with the physics of travelling at 200mph. The KE of a car increases with the square of the speed and hence the higher the speed the correspondingly much more difficult it is to contain the energy of the car if the unfortunate does occur.
True to a point but KE is only important to consider primarily if there is no stopping distance available, if no braking can take place before the KE is transferred, or if the (assumed) collision is a head-on between slab-sided objects of similar mass. In most real world situations, braking even of the oh sheeeeeeet kind (and crumple zone deformation) absorb most of the KE relatively harmlessly and dissipate it as heat in the brakes. If the point about KE refers to the unlikely possibility of impact with a pedestrian - we are talking motororways here - then KE is even less important, we should consider momentum as the collision will be inelastic. If not, and KE was conserved, you could be looking for the bodies of motorway suicides beyond the next junction.
Speedophobes have latched onto the KE thing and use it without thought for the actual physics, it's just a formula with a square law in it and that seems to be useful to them, but please note that's not an attack on this post as speedophobic. There are plenty of mechanical laws and dynamical ones too with higher powers but, of itself, just like speed, such matters are mostly 'academic'.
TIGA84 said:
Decanter said:
" defending what simply amounts to using excessive speed on an autobahn"
How can excessive speed occur on a road with no limits?Surely it could be considered excessive if, regardless of the lack of imposed limit, it was dangerous - for example in heavy traffic, high side winds, standing water, etc.
Joe911 said:
Surely it could be considered excessive if, regardless of the lack of imposed limit, it was dangerous - for example in heavy traffic, high side winds, standing water etc.
Absolutely. One of the formulae for describing surface tension has a square law in it, and potentially higher orders too... 
turbobloke said:
tony.t said:
You can't argue with the physics of travelling at 200mph. The KE of a car increases with the square of the speed and hence the higher the speed the correspondingly much more difficult it is to contain the energy of the car if the unfortunate does occur.
True to a point but KE is only important to consider primarily if there is no stopping distance available, if no braking can take place before the KE is transferred, or if the (assumed) collision is a head-on between slab-sided objects of similar mass. In most real world situations, braking even of the oh sheeeeeeet kind (and crumple zone deformation) absorb most of the KE relatively harmlessly and dissipate it as heat in the brakes. If the point about KE refers to the unlikely possibility of impact with a pedestrian - we are talking motororways here - then KE is even less important, we should consider momentum as the collision will be inelastic. If not, and KE was conserved, you could be looking for the bodies of motorway suicides beyond the next junction.
KE is important where there is a stopping distance. It takes twice as long to stop at 40 as it does at 30 as a result of the square law relating to KE. Also speed is not lost in a linear fashion. Using the 30/40 analogy above after half the braking distance from 40 has been reached you're still doing 30.
All of which is fine if there is adequate stopping distance and braking is controlled. However when not in control the higher KE does present a problem; A car is more likely to become airbourne for example or skids/slides will be much longer and much more difficult to recover.
KE transference to pedestrians are not inelastic as you well know . BTW the force on the pedestrian is directly proportional to the change in KE.
tony.t said:
turbobloke said:
tony.t said:
You can't argue with the physics of travelling at 200mph. The KE of a car increases with the square of the speed and hence the higher the speed the correspondingly much more difficult it is to contain the energy of the car if the unfortunate does occur.
True to a point but KE is only important to consider primarily if there is no stopping distance available, if no braking can take place before the KE is transferred, or if the (assumed) collision is a head-on between slab-sided objects of similar mass. In most real world situations, braking even of the oh sheeeeeeet kind (and crumple zone deformation) absorb most of the KE relatively harmlessly and dissipate it as heat in the brakes. If the point about KE refers to the unlikely possibility of impact with a pedestrian - we are talking motororways here - then KE is even less important, we should consider momentum as the collision will be inelastic. If not, and KE was conserved, you could be looking for the bodies of motorway suicides beyond the next junction.
KE is important where there is a stopping distance.
tony.t said:
It takes twice as long to stop at 40 as it does at 30 as a result of the square law relating to KE.
Well OK, 1.78 times to be pedantic, but like you say that's only important if you can't stop in that distance. tony.t said:
KE transference to pedestrians are not inelastic as you well know. BTW the force on the pedestrian is directly proportional to the change in KE.
Hang on - so if they're not inelastic they are elastic - no, that's just not right. You're saying that the car and pedestrian don't deform, and they sure do. BTW the force on the pedestrian isn't directly proportional to the change in KE. Remember impulse = change in momentum?
Ft = mv - mu
so F = change in momentum divided by time in contact
This gets the KE errors across nicely so worth it.
turbobloke said:
tony.t said:
turbobloke said:
tony.t said:
You can't argue with the physics of travelling at 200mph. The KE of a car increases with the square of the speed and hence the higher the speed the correspondingly much more difficult it is to contain the energy of the car if the unfortunate does occur.
True to a point but KE is only important to consider primarily if there is no stopping distance available, if no braking can take place before the KE is transferred, or if the (assumed) collision is a head-on between slab-sided objects of similar mass. In most real world situations, braking even of the oh sheeeeeeet kind (and crumple zone deformation) absorb most of the KE relatively harmlessly and dissipate it as heat in the brakes. If the point about KE refers to the unlikely possibility of impact with a pedestrian - we are talking motororways here - then KE is even less important, we should consider momentum as the collision will be inelastic. If not, and KE was conserved, you could be looking for the bodies of motorway suicides beyond the next junction.
KE is important where there is a stopping distance.
tony.t said:
It takes twice as long to stop at 40 as it does at 30 as a result of the square law relating to KE.
Well OK, 1.78 times to be pedantic, but like you say that's only important if you can't stop in that distance. tony.t said:
KE transference to pedestrians are not inelastic as you well know. BTW the force on the pedestrian is directly proportional to the change in KE.
Hang on - so if they're not inelastic they are elastic - no, that's just not right. You're saying that the car and pedestrian don't deform, and they sure do. BTW the force on the pedestrian isn't directly proportional to the change in KE. Remember impulse = change in momentum?
Ft = mv - mu
so F = change in momentum divided by time in contact
This gets the KE errors across nicely so worth it.
Really, blimmmmyyy.
.
Mark.
turbobloke said:
tony.t said:
turbobloke said:
tony.t said:
You can't argue with the physics of travelling at 200mph. The KE of a car increases with the square of the speed and hence the higher the speed the correspondingly much more difficult it is to contain the energy of the car if the unfortunate does occur.
True to a point but KE is only important to consider primarily if there is no stopping distance available, if no braking can take place before the KE is transferred, or if the (assumed) collision is a head-on between slab-sided objects of similar mass. In most real world situations, braking even of the oh sheeeeeeet kind (and crumple zone deformation) absorb most of the KE relatively harmlessly and dissipate it as heat in the brakes. If the point about KE refers to the unlikely possibility of impact with a pedestrian - we are talking motororways here - then KE is even less important, we should consider momentum as the collision will be inelastic. If not, and KE was conserved, you could be looking for the bodies of motorway suicides beyond the next junction.
KE is important where there is a stopping distance.
tony.t said:
It takes twice as long to stop at 40 as it does at 30 as a result of the square law relating to KE.
Well OK, 1.78 times to be pedantic, but like you say that's only important if you can't stop in that distance. tony.t said:
KE transference to pedestrians are not inelastic as you well know. BTW the force on the pedestrian is directly proportional to the change in KE.
Hang on - so if they're not inelastic they are elastic - no, that's just not right. You're saying that the car and pedestrian don't deform, and they sure do. BTW the force on the pedestrian isn't directly proportional to the change in KE. Remember impulse = change in momentum?
Ft = mv - mu
so F = change in momentum divided by time in contact
This gets the KE errors across nicely so worth it.
I have a sense of deja vu here. Previously, despite empirical and algebraically evidence to the contrary, IIRC you and a number of other posters simply refuse to believe that the KE (or if we're being pedantic the change in KE) increasing by the square of speed influences the resultant forces occurring in an accident. Since you were unconvinced last time I doubt if you will this.
However;
The point about braking distances is that you need more with increase in speed and that the increase in braking distance increases with the square of speed.
The ratio in the 30/40mph example is clearly 9:16 so if we're being pedantic 1.78 isn't correct.
I really don't recall saying car/pedestrian impacts were elastic and neither did I imply they were. There is no logic in your assumption that any inelastic collision is an elastic one. Neither did I say that a pedestrian or car don't deform. Would you care to quote me there?
The force is directly proportional to the change in KE.
Impulse or change in momentum does not alter that fact.
How exactly does your post correct any "KE errors" whatever they may be?
tony.t said:
The force is directly proportional to the change in KE.
Impulse or change in momentum does not alter that fact.
How exactly does your post correct any "KE errors" whatever they may be?
This seems to be a bit of a thread hijack (sorry adam). Impulse or change in momentum does not alter that fact.
How exactly does your post correct any "KE errors" whatever they may be?
"The force is directly proportional to the change in KE.
Impulse or change in momentum does not alter that fact."
It's not a fact, force is directly proportional to change in momentum divided by contact time. That's science. I don't know where you got the proportional to change in KE from, but it's not science.
As a last gasp hope of convincing you - and anyone else who might be the slightest bit interested in this diversion arising from adam's autobahn escapade - look to dimensional analysis. Force (which being equivalent to mass multiplied by acceleration, has units kg m/s^2) cannot be directly proportional to a change in KE (units kg m^2/s^2) but can be and is proportional to change in momentum (mass multiplied by velocity so kg m/s) divided by time (so divide by another s in the units and get kg m/s^2).
If we've disagreed on this before, forgive me for not remembering, but since then science hasn't changed. If you don't know / can't be bothered to check / want to believe your version, that's OK but there is no doubt at all, none whatsoever, that collisions between cars and people are inelastic, and equally no doubt that, even in 2006, force applied in a collision is proportional to the change in momentum divided by time of contact. That's it.
This is indeed far way from Adam's original post, but there is indeed
a link to the kinetic energy with the law of conservation of energy it seems
to me.
Whereas the sum 1/2mv2 for both objects:
- Object A: Adam's RUF's at 200mph velocity.
- Object B, an old lady or a toddler deciding to walk in the middle of an Autobahn at night time with a negligible velocity (Close to Zero).
The conservation of energy indeed would indicate that the energy transfered to object B (The victim...) is equal to the loss of energy from object A (Adam, the bloodthirsty 200mph maniac murderer...).
The sum of KE for both objects being constant.
Now, on the subject of the elasticity of the pedestrian, yes, they are soft, but that does not matter in view of the law of conservation of energy, in other word, since the mass of Adam's car and the pedestrian wil stay constant, the slower Adam's car after the chock, the worst off the poor and innocent pedestrian will be (Regardless of impact duration or any other factor).
Strictly speaking, both object A (Adam's RUF) and B (Happless socialist nightime Autobhan crossing victim) are not indeformable solids, they are elastic.
As Harry Vattanen said when interviewed during a Portugal rally with foolish spectators standing in the middle of the rally stage and parting as his car arrived and asked if he was concerned over the closeness of the spectators to his car: '' I am not vorried about ze specators zey are squishy, I am vorried about the trees and rocks.....''
a link to the kinetic energy with the law of conservation of energy it seems
to me.
Whereas the sum 1/2mv2 for both objects:
- Object A: Adam's RUF's at 200mph velocity.
- Object B, an old lady or a toddler deciding to walk in the middle of an Autobahn at night time with a negligible velocity (Close to Zero).
The conservation of energy indeed would indicate that the energy transfered to object B (The victim...) is equal to the loss of energy from object A (Adam, the bloodthirsty 200mph maniac murderer...).
The sum of KE for both objects being constant.
Now, on the subject of the elasticity of the pedestrian, yes, they are soft, but that does not matter in view of the law of conservation of energy, in other word, since the mass of Adam's car and the pedestrian wil stay constant, the slower Adam's car after the chock, the worst off the poor and innocent pedestrian will be (Regardless of impact duration or any other factor).
Strictly speaking, both object A (Adam's RUF) and B (Happless socialist nightime Autobhan crossing victim) are not indeformable solids, they are elastic.
As Harry Vattanen said when interviewed during a Portugal rally with foolish spectators standing in the middle of the rally stage and parting as his car arrived and asked if he was concerned over the closeness of the spectators to his car: '' I am not vorried about ze specators zey are squishy, I am vorried about the trees and rocks.....''
Edited by Gulliver911 on Thursday 17th August 23:00
Gulliver911 said:
- Object A: Adam's RUF's at 200mph velocity.
- Object B, an old lady or a toddler deciding to walk in the middle of an Autobahn at night time with a negligible velocity (Close to Zero).
The conservation of energy indeed would indicate that the energy transfered to object B (The victim...) is equal to the loss of energy from object A (Adam, the bloodthirsty 200mph maniac murderer...).
Gulliver011 said:
The sum of KE for both objects being constant.
As it happens, it's not, because some energy is used to deform the car and the pedestrian. That's what an inelastic collision is, KE is not conserved but momentum is. Gulliver911 said:
both object A (Adam's RUF) and B (Happless socialist nightime Autobhan crossing victim) are not indeformable solids, they are elastic.
Dodgy use of 'elastic' ! See above. The everyday use isn't the same as when applied to collisions. Try any physics texxt book or academic website such as one like this:
http://galileoandeinstein.physics.vir
virginia.edu said:
Momentum Conservation and Newton's Laws
As we have discussed above, Descartes introduced the concept of momentum, and the general principle of conservation of momentum in collisions, before Newton's time. However, it turns out that conservation of momentum can be deduced from Newton's laws. Newton's laws in principle fully describe all collision-type phenomena, and therefore must contain momentum conservation.
To understand how this comes about, consider first Newton's Second Law relating the acceleration a of a body of mass m with an external force F acting on it:
F = ma, or force = mass x acceleration
Recall that acceleration is rate of change of velocity, so we can rewrite the Second Law:
force = mass x rate of change of velocity.
Now, the momentum is mv, mass x velocity. This means for an object having constant mass (which is almost always the case, of course!)
rate of change of momentum = mass x rate of change of velocity.
This means that Newton's Second Law can be rewritten:
force = rate of change of momentum.
Now think of a collision, or any kind of interaction, between two objects A and B, say. From Newton's Third Law, the force A feels from B is of equal magnitude to the force B feels from A, but in the opposite direction. Since (as we have just shown) force = rate of change of momentum
The emphasis is mine but the result is clear. There is no academic text book or website that will tell you anything different, none that will say that force applied in a collision is proportional to change in KE, beause it isn't. If BRAKE or Roadpeace say different they are lying.
Perhaps we should get back to 200mph.
Turbobloke,
You said: As it happens, it's not, because some energy is used to deform the car and the pedestrian. That's what an inelastic collision is, KE is not conserved but momentum is.
Exactly, and the energy used for the deformation is coming from the 1/2mv2, the energy conservation very much applies with elastic objects.
I don't need to consult academic websites as this is actually a subject I did my thesis on.
Anyway, don't want to get into an argument, I am drunk right now (No Decanter, I am not driving, so don't even start.....)
Take care....
JLL
You said: As it happens, it's not, because some energy is used to deform the car and the pedestrian. That's what an inelastic collision is, KE is not conserved but momentum is.
Exactly, and the energy used for the deformation is coming from the 1/2mv2, the energy conservation very much applies with elastic objects.
I don't need to consult academic websites as this is actually a subject I did my thesis on.
Anyway, don't want to get into an argument, I am drunk right now (No Decanter, I am not driving, so don't even start.....)
Take care....
JLL
Edited by Gulliver911 on Thursday 17th August 23:25
Gulliver911 said:
Turbobloke,
You said: As it happens, it's not, because some energy is used to deform the car and the pedestrian. That's what an inelastic collision is, KE is not conserved but momentum is.
Exactly, and the energy used for the deformation is coming from the 1/2mv2, the energy conservation very much applies with elastic objects.
But elastic objects have inelastic collisions! You said: As it happens, it's not, because some energy is used to deform the car and the pedestrian. That's what an inelastic collision is, KE is not conserved but momentum is.
Exactly, and the energy used for the deformation is coming from the 1/2mv2, the energy conservation very much applies with elastic objects.
Total energy is conserved (of course) but KE is not. You spoke of adding up KE, and it won't work. "The sum of KE for both objects being constant" is what you posted (word for word) and it's not true is it? You now say it's the sum of the KE'a plus some energy lost in changing shapes - and that IS correct.
Thesis? What was its title? Was it related to science in any way? Obviously I didn't supervise you for your PhD or you'd know better
My own research thesis wasn't on mementum and I can't think of any that would be unless we're talking relativistic momentum and energy, but I'll take you at your word. In turn I could also point you to my own text books, though I haven't written that many at such a low level, but you'd call that biased and accuse me of continuing the dick waving contest you just started
Try this if you want more:
http://hyperphysics.phy-astr.gsu.edu/
that site said:
Elastic and Inelastic Collisions
A perfectly elastic collision is defined as one in which there is no loss of kinetic energy in the collision. An inelastic collision is one in which part of the kinetic energy is changed to some other form of energy in the collision. Any macroscopic collision between objects will convert some of the kinetic energy into internal energy and other forms of energy, so no large scale impacts are perfectly elastic. Momentum is conserved in inelastic collisions, but one cannot track the kinetic energy through the collision since some of it is converted to other forms of energy.
A perfectly elastic collision is defined as one in which there is no loss of kinetic energy in the collision. An inelastic collision is one in which part of the kinetic energy is changed to some other form of energy in the collision. Any macroscopic collision between objects will convert some of the kinetic energy into internal energy and other forms of energy, so no large scale impacts are perfectly elastic. Momentum is conserved in inelastic collisions, but one cannot track the kinetic energy through the collision since some of it is converted to other forms of energy.
Maybe somebody else who knows real science could chip in at this point, I'm giving up on flat earth pistonheading before the thread implodes...at which point thread momentum would be conserved but thread KE would not.
Ta
I did say conservation of KE in my post you are right....I meant conservation of energy all along, dissipated as inselastic deformation, heat dissipation, broken bones, etc.....
Must be those Stella Artois going at me....
PS: Thesis was finite element calculus on helicopter blade main load bearing beam (Glass) in a sandwich structure for Eurocopter, but that was a long time ago.....
Gulliver911 said:
I did say conservation of KE in my post you are right....I meant conservation of energy all along, dissipated as inselastic deformation, heat dissipation, broken bones, etc.....
Must be those Stella Artois going at me....
PS: Thesis was finite element calculus on helicopter blade main load bearing beam (Glass) in a sandwich structure for Eurocopter, but that was a long time ago.....
For quite a time post-grad (natural sciences) I was dabbling with the physical chemistry of planetary atmospheres, so most of the global warming threads see a post or two from me, but nowadays I've switched back to using my Part III maths voluntary work with some lecturing on bits of astrophysics to masters and postdoc international students. Miles away from the autobahn where I think this thread should now return at well over 200 mph - but I believe very strongly that the simplistic KE arguments as used by anti-speed pressure groups need challenging as it's all so plausible but also wrong.
turbobloke said:
"The force is directly proportional to the change in KE.
Impulse or change in momentum does not alter that fact."
It's not a fact, force is directly proportional to change in momentum divided by contact time. That's science. I don't know where you got the proportional to change in KE from, but it's not science.
Impulse or change in momentum does not alter that fact."
It's not a fact, force is directly proportional to change in momentum divided by contact time. That's science. I don't know where you got the proportional to change in KE from, but it's not science.
A simple exampleof force being proportional to change in KE; Braking from 40mph takes a longer distance to braking from 30mph and the respective distances follow the same ratio as the ratio for KE change. Since the force (braking force) is the same in both cases using F=ma I think you'll find that to stop in the same distance the braking force from 40 will have to be 16/9 x that from 30mph.
It can be no other way since the change in KE is due to a change in speed which by definition involves acceleration.
turbobloke said:
Force (which being equivalent to mass multiplied by acceleration, has units kg m/s^2) cannot be directly proportional to a change in KE (units kg m^2/s^2) but can be and is proportional to change in momentum (mass multiplied by velocity so kg m/s) divided by time (so divide by another s in the units and get kg m/s^2).
The units involved do not preclude proportionality
example: distance covered is proportional to speed travelled even though the "units" are different. Since both have mass (kg) in their "units" it's a bit of a giveaway they ( KE and Force) will be proportional. Look at the relevant equations F=ma and KE=1/2 mvv or put another way F/a=2KE/vv
turbobloke said:
If we've disagreed on this before, forgive me for not remembering, but since then science hasn't changed. If you don't know / can't be bothered to check / want to believe your version, that's OK but there is no doubt at all, none whatsoever, that collisions between cars and people are inelastic, and equally no doubt that, even in 2006, force applied in a collision is proportional to the change in momentum divided by time of contact. That's it.
Collisions between cars and people are neither elastic or in elastic but are complex (being partialy both elastic and inelastic and to varying degrees depending on the tissue type)
Momentum is still irrelevant to the fact change in KE is proportional to the forces involved in that change.
Like I said before, this is now not helpful and certainly not funny, the 'science' you quote is quite wrong but never mind, please feel free to continue thinking you're right. There are so many basic errors in your re-statements of non-science that I would be lost for a suitable place to start from, and as it's been done already - the posts are here for anyone with the interest, the knowledge and the patience to wade through - the diversion ought to hit a 'road closed' sign at this point.
Time for a U turn, back to the autobahn...
Time for a U turn, back to the autobahn...
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