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crash tests

Huw and Robert are arguing basic physics:

> Sorry, Huw.  Your reasoning is flawed.
> Imagine a car striking an immovable barricade.

No barricades involved, so why "imagine" any?

>  In effect, each car becomes the other car's immovable barricade.

Nope.  In the 60/0 collision, the CAR being hit ends up moving at 30 mph
(less friction losses to the road) in the direction the 60 mph car was
going.  Try it any time.  maybe with something cheaper than cars, and
slower, and smaller...

Huw Powell

My semi educated $.02:

Hey, you guys got most of this stuff right, it's the details that make the 
difference.  Crumple zones deforming absorb energy from the 0.5MV^2 
equation so that resultant energy of system that a passenger would 
experience is less than apparent with non compressible vehicles (no 
crumpling of car(s)).  Earlier someone also mentioned that the rate of 
deformation and "big hit" energy transfer also strongly correlates to the 
level of damage to occupants.  Energy can be related back to force applied 
over time, and the end result ...  F=M*A, so if the overall energy that the 
passenger sees is still big, his or her mass doesn't change and the only 
thing left to do is accelerate ... passengers head, body, etc (the thing 
that really matters here).  There's lots of other variables also - the 
resultant force vector is determined by angles between the hittee's - if a 
car traveling down the road strikes a car at less than directly head on, 
the force vector has a component that goes perpendicular to the road, which 
also lessens the head on impact energy component (car(s) tries to spin as a 
result).  All of the variables get real ugly to try and predict theory on - 
better to instrument and do empirical parametric studies with models and 
scale up uncertainties and etc. unless you have lots of bucks to crash 

Great way to demonstrate is the first year engineering school experiment of 
protecting an egg from 30 foot fall where winner has the lightest 
protection system with an undamaged raw egg.  Lengthy deformation period of 
"cage" resulting in lower accelerations for the eggs crash protection 
system, ie shell.  I think I used some perforated styrofoam cups filled 
with shaving cream and guide vanes for flight control - very light, very 
effective.  BTW, the floor in this case was uncompressible so the system 
was easier to design for!

-Randy - long time removed from school, so go light on flaming possible 
errors in phsyics memories!
'90 200Q w/ lots of mass