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Re: Gasoline prices



Art Hobson...

I really appreciated the facts and figures in your message below.
It is really a mind-boggling reawakening on the comparative
uses of our transportation devices. I hope that your textbook is
selling well ....especially to the high school and college non-science-
major students.... who can really benefit from this approach.

Herb
-
On Tue, 27 Jun 2000 09:08:22 -0500 Art Hobson <ahobson@COMP.UARK.EDU>
writes:
Rather than just whining about the effect of gasoline prices on our
own
pocketbooks, Americans should begin a meaningful social
consideration of
energy issues. We physics teachers can help, by including
energy-and-society issues in our introductory courses. For
starters, here
are some figures on transportation efficiency:

Table 1. Passenger-Moving Efficiencies Of Different Human
Transportation Modes, In Passenger-km/megajoule:
Human on bicycle 18.0 pass-km/MJ
Human walking 5.0
Intercity railroad train 1.7
Urban bus 0.9
Carpool auto (occupancy=4) 0.7
Commercial airplane 0.4
Commuting auto (av occ=1.15) 0.2

Table 2. Passenger-Moving Efficiencies Of Animals
And Machines In kg-km/MJ (i.e. mass-moving
efficiency, incl the mass of passengers):
Human on bicycle 1100 kg-km/MJ
Typical fish 600
Horse 500
Human walking 300
Typical bird 200
Intercity railroad train 100
Urban bus 55
Hummingbird 50
Carpool auto 40
Commercial airplane 40
Fly, bee 20
Commuting auto 12
Mouse 5
Source: S. Wilson, "Bicycle Technology," Scientific American March
1973.
Comment: There are two basic physical reasons for the pre-eminence
of the bicycle in Tables 1 and 2: Newton's first law (wheeled
vehicles are
favored because, by rolling, they take advantage of their own
inertia) and
the second law of thermodynamics (among wheeled vehicles, all are
heat
engines except the bicycle, and heat engines at Earth-like
temperatures
must run at low efficiency).

Table 3. Freight-Moving Efficiencies, in kg-km/MJ:
Railroad train (freight) 3100 kg-km/MJ
Truck (heavy) 490
Airplane (freight) 74
Comment: Again, there are fundamental reasons for the train's
outstanding efficiency: It's air resistance, per kg of freight, is
lowest because a single engine can haul so much, and it rolls
much better than a truck because steel wheels on a steel road
have negligeable bounce (i.e. rolling resistance).


Art Hobson, Physics, U Arkansas, Fayetteville, AR 72701
See info about my liberal-arts physics textbook at
http://www.uark.edu/depts/physics/about/hobson.html