[DML] Re: crash tests / safety

["dmc12rb" <rbrogren@xxxxxxx>]

We have seen a fair amount of discussions on this subject, but many 
of them are opinions and presumed logic. 

The engineering facts are:

A "barrier test" and a head-on collisions in this argument are 
fundamentally different. While in both instances the vehicle(s) will 
theoretically stop upon collision (assuming equal masses in the case 
of a head-on), the crash speed is cumulative. IE: if barrier = 40 
mph, head-on = 80 mph = 40 mph + 40 mph. 


This is easier to imagine if you consider the amount of energy 
involved in a crash (energy/power balance)... the momentum (power) 
associated with a "barrier" collision is equal to the speed times the 
mass of the one vehicle (say 40 mph*1500 lbs= 60,000 mile-pounds per 
hour, or a somewhat more standard 11.36 ft-lb[mass]/hr), while the 
head-on involves twice the velocity and twice the mass (effectively 
2*11.36 fl-lbs[mass]/hr). Thus twice the energy is dissipated in a 
head-on than in a "barrier" collision. 


Think about which would make a bigger bang (or try it!)... sliding 
one block into a solid wall, or sliding two blocks (at the same 
speed) into each other... try putting your finger in between them, 
and tell me which one hurts more. 

Roger Brogren
VIN 1074





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