Re: crash tests

[Robert Myers <rmyers@inetone.net>]

Huw,

Look at the collision as two separate accidents.  One car traveling west
(let's say) strikes an obstacle and comes to an almost instant stop from 30
mph to zero mph.  A second identical car traveling east at 30 mph strikes
an obstacle and almost instantly stops moving.  The change in kinetic
energy in each case is KE = (mV^2)/2.  Each car "releases" that amount of
energy.  True, the total energy is double because there are two cars but it
is spread over two cars, not one.

BTW a single car traveling at 60 mph striking a barricade releases four
times as much energy as the same car traveling at 30 mph would release, not
double.  Remember, the energy change is proportion to the *square* of the
velocity change.



At 12:00 PM 12/13/1999 -0500, you wrote:
>>                 ... Be aware that two cars travelling towards each other,
>> each at 30 MPH is an extremely severe collision, visually, it would LOOK
>> like driving into a parked car while you were doing 60 MPH, brakes OFF.
>> 
>> I believe physics shows us that 2 cars head-on each going 30mph is not the
>> same as 1 car going 60 into a parked car. 
>
>I believe you're wrong...
>
>> Each car absorbs 30mph, not 1
>> absorbing none (unless it is a semi-truck) and the other car absorbing all.
>> Small point, but a common misconception.
>
>the total energy is the same.  relatively speaking the two cars (A at 30
>and B at 30 or A at 60 and B at 0) could be going any speed relative to
>the observer.  they are travelling 60 mph relative to each other.  
>
>Try it sometime, actions speak louder than... oops, maybe don't!
>
>-- 
>Huw Powell
>
>http://www.humanspeakers.com/audi/
>
>
___
   Bob
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