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This week---

This week---. Monday: “EMERGY”– how much energy does it take to extract energy? Reading: wikipedia is ok www.greatchange.org/footnotes-emergy.html Wednesday: Start Ch. 8, Transportation Friday: Transportation Next Wednesday March 17—EXAM 2, Ch. 5-9. US transportation energy.

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This week---

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  1. This week--- Monday: “EMERGY”– how much energy does it take to extract energy? Reading: wikipedia is ok www.greatchange.org/footnotes-emergy.html Wednesday: Start Ch. 8, Transportation Friday: Transportation Next Wednesday March 17—EXAM 2, Ch. 5-9

  2. US transportation energy Table 1.3- transportation uses 27.3% of US energy Table 8.1- transport uses 4.7x109 bbl/year Fig. 2.2-we produce 2x109 bbl/year daily average 4.7x109 bbl/yr x 42 gal/bbl / 3x108 x 365 days/yr =1.8 gal per person each day Transport based upon petroleum—energy density, Monday.

  3. Forces for transport • To get moving, accelerate: F =ma • To go uphill: F=mg x slope • Rolling friction: F =mass x speed x constant • Air friction: F=area x speed 2 x constant

  4. To accelerate: • one ton car=2000 pounds, zero to 60 in 10 sec. (60 mph=88 ft/sec) • F= m a = 2000/32 x 88 ft/sec/10 sec=550 pounds Force needed from the engine to get the car into motion, with kinetic energy.

  5. To climb 5% slope Force= weight x slope=2000 pounds x 0.05 =100 pounds

  6. Rolling friction at full speed Force = constant x mass x speed =0.01 x 2000/32 x60 mph =38 pounds

  7. Air friction at full speed 1981 Cadillac (Table 8.3) Force = ‘drag’ x frontal area x speed2 /370 =0.55 x(4 x 6) 602 /370 = 128 pounds

  8. Rules to remember! • Rolling force, to keep moving ~ speed and mass • Aero force to keep moving ~ speed squared

  9. Force, power and energy • Power = energy/time =(work=force x distance ) / time = force x speed Rolling power ~ v2 (and mass) Aero power ~ v3 (as wind power, page 134) • Energy=force x distance Rolling ~ v x mass x distance Aero~v2 x distance

  10. Engine efficiency • How much of the energy in the fuel can be applied to these frictions? • Fig. 8.1--.about 15% • Thence, miles per gallon=energy in one gallon of fuel/work done to overcome friction in traveling one mile • Examples 8.2 and 8.3

  11. mpg example Aero friction alone = 128 pounds of force Travel one foot work = 128 ft pounds=174 J Travel one mile- work = 174x5280 = 919,143 J mpg=(miles/Joule )/ (gal/Joule) =1/919,143 / 1/1.32 x108 =1.32x108/9.19x105=145 mpg (but, at 15%, really 0.15x145=21.8 mpg)

  12. What to remember? Mpg comes from – • engine efficiency • Shape and frontal area (aerodynamic) • Mass(weight)- for the rolling friction • Speed (rolling) • Speed squared (aero)

  13. Speed limits-- Lower from 75 mph to 55— • Rolling force55/75=0.73 • Rolling work energy55/75=0.73 • Force through the air(55/75)2 =0.54 • Aero drag work (55/75)2=0.54 • Time for the trip75/55=1.36 • Hazard ~ kinetic energy ~(55/75)2=0.54 (example 8.5)

  14. HW #9 due March 15 EXAM #2 Wednesday in class March 17 1.(10) It is desired to fly one liter (1 kg) of Yuppie Water from Suva, Fiji to Denver, a distance of 6329 miles. Neglecting the difference between an English ton and a metric tonne, how many barrels of jet fuel (the same energy content as crude oil) will this require? If that refined fuel costs $100 per barrel, what was the cost of shipping that water? 2.(4) The answer to Problem 1 seems to be costly, so I use an old airplane that flies with the same ‘drag coefficient’ and other flight features as the original one, but at half the speed. By what factor does the aircraft power requirement change? By what factor does the fuel consumption to bring that liter to Denver change?

  15. Friday- • How to improve transport efficiency • “ton-miles”, “passenger-miles” • Mileage standards • Biofuels

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