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).