Re: Bicycles, trucks, trains

[Richard Tarara <rtarara@SAINTMARYS.EDU>]

----- Original Message -----
From: Leigh Palmer <palmer@SFU.CA>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, September 16, 1999 11:09 AM
Subject: Re: Bicycles, trucks, trains


> At 8:20 AM -0700 9/16/99, Laurent Hodges wrote:
>
> > I remember also their insistence that driving 65 mph was really more
> > energy-efficient (as well as time-efficient) than driving 55 mph.  The
> > Department of Energy (or maybe ERDA in those days) did a test with a
group
> > of identical trucks driving an identical route all around Virginia, but
> > going at different maximum speeds.  The slowest (30-mph) truck was the
most
> > energy-efficient, of course, blowing the truck drivers' argument away.
>
> I teach my thermodynamics students that "efficiency" when used in the
> technical sense means exactly what Prof. Hodges means here. Somehow
> the term "figure of merit" doesn't seem to be known to them, so I
> introduce it using, of course, refrigerators. My definition:
>
>                         the value of what you get that you want
>    figure of merit = ---------------------------------------------
>                       the cost of getting it that you have to pay


Of course you can also look at the truckers problem solely from an energy
point of view, but in much more detail.  What you really want is the cost,
energy or $, per weight of cargo delivered.  The 30 mph truck will take a
lot longer to deliver and now involve sleeping time (often done in the truck
with the engine running), extra meals, maybe a change of clothes (and the
energy to wash and dry those), etc.   This 'extra' energy expended to
deliver the cargo could well wipe out a small difference in mpg fuel
efficiency.

Clearly Leigh has little respect or belief in global energy problems (and he
has certainly railed against the notion of global warming) so it would be of
little use to suggest that the finite and politically fragile nature of
fossil fuel supplies and the strong possibility that the (non-existent)
global warming may trigger a freeze on the use of such fuels might well
produce another 'energy crisis' in the foreseeable future--along with a
whole new set of 'silly' solutions.  ;-)

Rick

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Richard W. Tarara
Department of Chemistry & Physics
Notre Dame, IN 46556
219-284-4664
rtarara@saintmarys.edu

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