Re: [Phys-l] truck mileage

[Richard Grandy <rgrandy@rice.edu>]

That is assuming steady speed on level ground--accelerating from a 
stop or going up hill would seem more costly with the cows.

Richard Grandy
(in Houston, where it is all level ground)

> Hi all-
>  	Of course all such data need to be taken with a few grains of
> salt, and driving habits can play a major role in the result.  But,
> consider the physics of a truck pulling a trailer at constant speed on a
> level road.  Power required be the presence of the trailer is that
> dissipated by the rolling friction of the trailer wheels.  How much does
> that friction increase when a load is placed obn the trailer?  I don't
> have much feel for the numbers, but it must be a small fraction of the
> added load.   The gal/mi is proportional to the friction force, which is
> probably proportional to some power of the speed.  My conclusion is that
> in all likelihood, a small decrease in the speed could compensate for the
> added friction due to the increased load.
>  			Regards,
>  				Jack
>
>
>
> On Wed, 7 May 2008, Bill Nettles wrote:
>
> >  I agree the data are questionable
> >
> >  OR
> >  the truck driver doesn't go as fast when he has 10000# of cows :)
> >
> >  Is there a baseline gas mileage with a nonlinear increase 
> > (arctangent) as the weight decreases? Gas mileages are notoriously 
> > non-linear for most variables.
> >
> > > > >  Kathy Daniel <kcdohs@comcast.net> 5/7/2008 4:02 pm >>>
> >  I have quite an interesting problem that I cannot explain...
> >
> >  Our Ag teacher set up this scenario for me:
> >
> >  one 5000# truck gets about 18 miles per gallon
> >  same 5000# truck pulling a 4000# trailer gets 8 miles per gallon
> >  same 5000# truck pulling a 4000# trailer + 10000# of cows ALSO  gets 8
> >  miles per gallon.
> >
> >  Any ideas why the empty and the full trailer both get the same
> >  mileage?  This same pattern is also present in a different trailer and
> >  truck combination.
> >
> >  thanks,
> >  Kathy
> >
> >
> >  Kathy Daniel
> >  Oakland High School
> >  Murfreesboro, TN  37130
> >  kcdohs@comcast.net
> >
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>  		just before leading them into the Little Big Horn Valley
>
>
>
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--
Richard E. Grandy
Professor
Philosophy & Cognitive Sciences
Rice University
Houston, TX USA