Re: [Phys-l] truck mileage

[Jack Uretsky <jlu@hep.anl.gov>]

	Also, if you carefully aligm the cows so that there is a bit of 
added thrust from their injections of methane into the atmosphere, you 
might be able to get a bit of added thrust.  This could be recognized as 
the "hayburner" (by analogy to "afterburner") effect.
				Regards,
					Jack





On Wed, 7 May 2008, John Denker wrote:

> On 05/07/2008 02:02 PM, Kathy Daniel wrote:
>
> > 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.
>
> 0) We have to assume the speed profile is the same in all cases,
> otherwise there is no hope of making sense of the problem.
>
> 1) This is obviously fake data.  I'm not going to say anything
> very nice about fake data.
>
> 2) However, one can come up with a scenario where this data is
> not completely wacky.
>
> The principal losses for a vehicle are:
> a) Rolling resistance (tires and bearings).
> b) Aerodynamic drag.
> c) Braking (and starting).
> d) Internal losses in the engine.
>
> In steady low-speed cruise, (a) and (d) dominate.
> In steady high-speed cruise, (b) dominates.
> In stop-and-go traffic, (c) dominates.
>
> So if we assume steady high-speed cruise, it is plausible that
> added mass might not make much of a difference.
>
> If you want to grasp at straws, you could cobble up scenarios
> where a stake-truck full of cows would be /more/ streamlined
> i.e. more aerodynamic than an empty stake truck.
>
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