Re: momentum

[Roger Haar <haar@PHYSICS.ARIZONA.EDU>]

Hi,
        The important question is what is delta v or delta
momentum?  hitting the equivalent car gives a delta v of 35
mph
but hitting the tree gives a delta v of 70 mph. The other
factor is impact time.  Big trees give very little, but the
front of cars crumple spreading out the impact in time.

Thanks
Roger Haar U of AZ

*************************************
"David J. Hamilton" wrote:
> Henry Kuhlman writes:
>
> > In the Cover Story of the Wed 30 June 99 USA Today, Edward Moeller, a
> > traffic engineer is quoted, "If you are driving 35 and hit someone coming
> > at you at 35, it's the equivilent of hitting a tree at 70."
> >
> > Any hope of correcting this WRONG PHYSICS?
>
> Am I missing something?  It seems that we can take any inertial frame of
> reference to analyze this case, including one where the other car is at
> rest and my car is approaching it at 70 mph.
>
> Of course hitting a car at 70 mph and hitting a tree at 70 mph are
> entirely different things -- is this the error you are referring to?
>
> Dave
>
> David J. Hamilton, Ed.D.          *  And gladly woulde he learn,
> Portland Public Schools           *  and gladly teche.
> djhamil@teleport.com              *        - Chaucer