Drive a Porsche? Are you a "target"?
08-01-2005, 08:29 PM
#32
Three Wheelin'
The math that folks do to call that a "70 MPH impact" is false. IF the two cars are of equal mass, it is 2 - 35 MPH collisions, or similar to TWO cars hitting a stationary wall at 35MPH each. Yes, the closure rate is 70mph, but since neither car has inertia in excess of 35mph it isn't like a 70 mph hit. IF one vehicle's mass is much larger, say an Excursion, Hummer or Locomotive, where the larger transfers it's energy to the smaller throwing it backward at a rate of say, 20 MPH, it might generate the G's of a 55mph hit.
BWise
08-01-2005, 11:20 PM
#33
Drifting
Originally Posted by 944Fest (aka Dan P)
Just for conversation's sake..
The math that folks do to call that a "70 MPH impact" is false. IF the two cars are of equal mass, it is 2 - 35 MPH collisions, or similar to TWO cars hitting a stationary wall at 35MPH each. Yes, the closure rate is 70mph, but since neither car has inertia in excess of 35mph it isn't like a 70 mph hit. IF one vehicle's mass is much larger, say an Excursion, Hummer or Locomotive, where the larger transfers it's energy to the smaller throwing it backward at a rate of say, 20 MPH, it might generate the G's of a 55mph hit. I'm not college educated, so math/physics majors feel free to chime in to correct me.
Again, just for conversation.. No flames intended..
The math that folks do to call that a "70 MPH impact" is false. IF the two cars are of equal mass, it is 2 - 35 MPH collisions, or similar to TWO cars hitting a stationary wall at 35MPH each. Yes, the closure rate is 70mph, but since neither car has inertia in excess of 35mph it isn't like a 70 mph hit. IF one vehicle's mass is much larger, say an Excursion, Hummer or Locomotive, where the larger transfers it's energy to the smaller throwing it backward at a rate of say, 20 MPH, it might generate the G's of a 55mph hit. I'm not college educated, so math/physics majors feel free to chime in to correct me.
Again, just for conversation.. No flames intended..
08-01-2005, 11:24 PM
#34
Drifting
Originally Posted by 2BWise
The amount of energy in the accident is figured with overall velocity equal to 70 mph if the vehicles are of equal mass. Its the same as if one car was stationary and the other was going 70, or one going 10 and the other 60, or whatever other combination of speeds that equate to 70mph.
BWise
BWise
08-02-2005, 12:23 AM
#35
Unaffiliated
Originally Posted by Scootin159
You got me thinking when I read this....but I think you have to figure in the energy absorbed by the cars. If one car is 100% stiff and the other does all the deformation, then yes....it's a 70mph impact for the softer car, but if they deform equally then it's just a 35mph impact for both of them (70mph of impact / 2 vehicles absorbing it)
08-02-2005, 12:34 AM
#36
Unaffiliated
Originally Posted by 2BWise
The amount of energy in the accident is figured with overall velocity equal to 70 mph if the vehicles are of equal mass. Its the same as if one car was stationary and the other was going 70, or one going 10 and the other 60, or whatever other combination of speeds that equate to 70mph.
BWise
BWise
08-02-2005, 01:15 AM
#37
Campeck Rulez
Rennlist Member
Rennlist Member
that crash was not engineering. there comes a point in an impact where no ammount of metal or stiffness is going to help. any car that goes sideways and hits a pole at over 60mph is going to be destroyed.... he got lucky. if a 944 rearends another vehicle and the other vehicles reaend is now nowhere to be found..but you can still see your hoodcrest. thats engineering. not someone being lucky as hell to walk out of a car that curled itself around a pole.
ah whatever.
ah whatever.
08-02-2005, 02:08 AM
#38
Pro
I think a head-on collision is more severe than two 35 mph collisions, because a normal 35 mph collision involves hitting something else that absorbs part of the energy, such as a tree or light pole or whatever. With a head-on collision, there is nothing else absorbing the impact energy except for the cars. It is like having each car crash into an infinitely strong object.
08-02-2005, 09:32 AM
#39
Three Wheelin'
You got me thinking when I read this....but I think you have to figure in the energy absorbed by the cars. If one car is 100% stiff and the other does all the deformation, then yes....it's a 70mph impact for the softer car, but if they deform equally then it's just a 35mph impact for both of them (70mph of impact / 2 vehicles absorbing it)
. If two cars nail head on, both 35 MPH and come to a dead stop instantly, there is nothing there other than 2 x 35 MPH impacts to a dead stop. Anyone else have input?
EX: car A and B both travelling 35 mph in opposite directions and both of equal mass as you stated early.
A and B collide head on. A will send energy into B and B will send energy into A. The calculations of this show that the energy is proportional to the COMBINED velocities, therefore 70mph.
If A hit a wall head at 35 mph, the wall does not move therefore has no kinetic energy, no velocity, so the velocity of the system is only 35.
If you want a more formal explanation w/the equations I'll write it up because I don't know if this is enough.
BTW, quick resume: third year mech eng student, FSAE, and 6 months of professional automotive engineering experience.
08-02-2005, 12:05 PM
#40
Unaffiliated
2Bwise, That is a good explanation. I started a thread in the OT about this, but I guess only members can go there. It is interesting the ASE guys and physics guys are on two different sides of it. I agree there definately is a combined energy of 70 MPH in the collision, but does it feel like, is it similar to, a 70 mph hit to either car? I don't believe so.
I'm going to copy your text in to the other thread if you don't mind, thanks!
I'm going to copy your text in to the other thread if you don't mind, thanks!
08-02-2005, 12:10 PM
#41
Addict
Rennlist Member
Rennlist Member
Join Date: Mar 2005
Location: Cairns, FNQ, Australia and Macau SAR
Posts: 2,155
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by 944Fest (aka Dan P)
Check out the new thread I started in OT on this subject.
(edit: I'm sorry, I see you aren't a member so you can't check it..don't worry, OT is often not worth visiting)
(edit: I'm sorry, I see you aren't a member so you can't check it..don't worry, OT is often not worth visiting)
And I beg to differ. OT is my favourite #2 place! Everybody there is nuts! LOL
BTW: Is this OT?
08-02-2005, 12:43 PM
#42
Nordschleife Master
In response to 2bwise's explanation.....I think that I disagree with what he said but I'm not totally clear as to what he meant.
I assume that cars A and B have the same mass.
If A hits a wall at 35mph, its a 35mph collision and all of the energy is dissipated by the car because the wall just sits there.
If A and B get into a headon at 35mph, energy of the system (kinetic energy cannot be negative) is double car A hitting a wall (because each car has 35mph velocity), but there are 2 cars, so energy absorbed by each car is 1/2 the total energy of the system or the equivalent of car A hitting a wall at 35mph.
Resume: Well, my dog said I'm smrt.... and 4th year mech E + FSAE + 3 years of private tutoring by Albert Einstein using the time machine I invented. But regardless this is late HS/1st year college type of stuff.
I assume that cars A and B have the same mass.
If A hits a wall at 35mph, its a 35mph collision and all of the energy is dissipated by the car because the wall just sits there.
If A and B get into a headon at 35mph, energy of the system (kinetic energy cannot be negative) is double car A hitting a wall (because each car has 35mph velocity), but there are 2 cars, so energy absorbed by each car is 1/2 the total energy of the system or the equivalent of car A hitting a wall at 35mph.
Resume: Well, my dog said I'm smrt.... and 4th year mech E + FSAE + 3 years of private tutoring by Albert Einstein using the time machine I invented. But regardless this is late HS/1st year college type of stuff.
08-02-2005, 12:44 PM
#43
Nordschleife Master
Originally Posted by MTM
I think a head-on collision is more severe than two 35 mph collisions, because a normal 35 mph collision involves hitting something else that absorbs part of the energy, such as a tree or light pole or whatever. With a head-on collision, there is nothing else absorbing the impact energy except for the cars. It is like having each car crash into an infinitely strong object.
08-02-2005, 02:47 PM
#44
Three Wheelin'
I can't go OT with this 
Someone post this for me please, or just reply here, whatever.
I've thought about it adrial and agree with you ... on the collision for two cars at 35 mph, but I was considering the general collision at any velocities. When their velocities are the same I agree it will "seem" like a 35 mph collision to both vehicles but this is a special case. Assume that the velocities are anything but equal and you will see that this should not be the case. The speed of the collision will "seem"/be different for each car when they are going different speeds.
Someone post this for me please, or just reply here, whatever.
I've thought about it adrial and agree with you ... on the collision for two cars at 35 mph, but I was considering the general collision at any velocities. When their velocities are the same I agree it will "seem" like a 35 mph collision to both vehicles but this is a special case. Assume that the velocities are anything but equal and you will see that this should not be the case. The speed of the collision will "seem"/be different for each car when they are going different speeds.
