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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / February 2006physical meaning of GasMileage expressed as an Area?
Quoting from page 64 of Brit magazine _New Scientist_ dated 26 Feb 2005 [reader Chris Bolton points out that fuel efficiency can be expressed, not only as distance/volume (eg, miles/gallon) but also as volume/distance (eg,] "liters/100 kilometers[ ) ]. But that's length-cubed divided by length, which is an area. With Google [unit converter]'s help, Bolton computed that the area achieved by his car is 0.05 square millimetres. Which, if you think about it, would be the cross-sectional area of the continuous thread of fuel required to feed the vehicle." Well, I did think about it, trying to decide what is the physical reality of that area. At first I thought it might be the area of the total nozzle aperture of the fuel injectors. But! flow doesn't solely depend upon aperture, but rather also upon the pressure at which the fuel is pumped. And anyway, a flowing "thread" of fuel does have three dimensions. So does this fuel-efficiency expressed as an area have a physical meaning? Is it the area under the curve of anything? Dear dances_with_barkadas: ... > So does this fuel-efficiency expressed as an area > have a physical meaning? Is it the area under the > curve of anything? No. It makes no more sense (on its own) than the resistivity of a material, which is unit length over unit area (ultimately). David A. Smith <snip> > So does this fuel-efficiency expressed as an area have a physical > meaning? Is it the area under the curve of anything? The 'area' is an artifact of the proxies used to measure energy consumption and work. It would be closer to the truth to use joules instead of liters / gallons of petrol / gasoline and joules of 'deliverable work' instead of kilometers / miles travelled. Just not as convenient... The ration would then tell you something about efficiency. Think about it: your 'mileage' should depend on a lot of other things that don't get into the calculation, such as octane rating, speed, headwind, engine rpm, and so on. Tom Davidson Richmond, VA ><snip> >> So does this fuel-efficiency expressed as an area have a physical >> meaning? Is it the area under the curve of anything? >The 'area' is an artifact of the proxies used to measure energy >consumption and work. It would be closer to the truth to use joules >instead of liters / gallons of petrol / gasoline and joules of >'deliverable work' instead of kilometers / miles travelled. Just not >as convenient... >The ration would then tell you something about efficiency. >Think about it: your 'mileage' should depend on a lot of other things >that don't get into the calculation, such as octane rating, speed, >headwind, engine rpm, and so on. Miles/gal (or litres/km or whatever) is actually an inverse area, not an area. Its inverse (gallons/mile) is an area. This area can be represented as this: Imagine a tiny trough of gasoline along a road, and a car with a scoop to get all its fuel out of the trough. The cross sectional area of the trough is the size the car needs to travel along this road. The larger the miles/gallon figure is, the smaller the trough needed to fuel the car. In theory, of course, as in reality there are numerous problems, such as gasoline evaporating, flowing downhill, someone coming along with a match etc. The total volume of the trough also has meaning. It is the amount of gasoline needed to run its length. convert to moles per horsepower at a gambol, please; thank *you*. thus: I was going to say that the "map, below," was 3-colorable, but the formatting became clear upon clicking for replying. anyway, that is also the "neccesity" part of the 4-color proof, a.k.a. "the tetrahedron, q.e.d." on a sphere (more or less; your further result is the same, as coloring/labelling the surrounding space .-) > Please explain how a map demanding 5 colors can demand 5 colors without > having 5 countries bordering each other? Anything except the specious [quoted text clipped - 7 lines] > | |______| | > |__________ |___________ | > If the analogy were valid, you could add country E between B & D, just > below C and get a 5-color map . And there are no 5 countries bordering > each other. > But the analogy is not valid. Adding E actually makes the map 3-C. > ------------------------------------------ > | A | [quoted text clipped - 3 lines] > | |______| | > |_______ |__E__|_________| --Give Earth a Trickier Dick Cheeny -- out of office, after gigayears! http://larouchepub.com/other/2003/3045dems_dive_soros.html http://tarpley.net/bush8.htm http://www.benfranklinbooks.com/ http://members.tripod.com/~american_almanac http://www.wlym.com/pdf/iclc/howthenation.pdf http://larouchepub.com/other/2003/3048iraq_58_const.html http://www.rand.org/publications/randreview/issues/rr.12.00/ http://www.rwgrayprojects.com/synergetics/plates/figs/plate01.html > <snip> > [quoted text clipped - 15 lines] > Tom Davidson > Richmond, VA Air travel is the safest form of public transport. The shuttle system is even safer, having lost only two shuttles. The shuttle travels at 7 passengers *17,000 mph ~= 120,000 passenger miles per hour. Walking a baby buggy is definitely NOT safe at only 4 passenger miles per hour. Shuttles are 30,000 times safer than baby buggies. I don't know why young mothers put their children at risk like that. Androcles. >> <snip> >> [quoted text clipped - 24 lines] > I don't know why young mothers put their children at risk like that. > Androcles. 2 shuttles out of what? 8, 3 of which are non-functional. That means we've lost 2 out of 5, that's a 40% loss. There are no ways that baby buggies are lost at that rate. >>> <snip> >>> [quoted text clipped - 28 lines] > we've lost 2 out of 5, that's a 40% loss. There are no ways that baby > buggies are lost at that rate. Safety is measured by passenger miles, the airline industries all agree the more passenger miles there are the safer it is. Besides, babies grow out of baby buggies faster than astronauts grow out of shuttles, the attrition rate is enormous. A baby buggy lasts for only 2 years. If you take a walk for 1 hour a day, that's 730 hours for the life of a baby buggy. Same for most cars, really. Cars cost say $20,000, add insurance and fuel and maintenance, call it $40 an hour. Makes me wonder how I ever afforded one. I shoulda been an airline pilot and travelled for free. Staying home is an even less safe form of transport. You get ZERO passenger miles that way. Androcles. > >>> <snip> > >>> [quoted text clipped - 41 lines] > Staying home is an even less safe form of transport. You get ZERO > passenger miles that way. Airline "passenger miles" measure the distance between the starting airport and the destination airport. Under those rules, how many miles does the average shuttle fly? > Airline "passenger miles" measure the distance between the starting airport > and the destination airport. Under those rules, how many miles does the > average shuttle fly? About 2500 miles if they land it in Edwards. About 3 miles if they land back at Canaveral ;-) | > Airline "passenger miles" measure the distance between the starting airport | > and the destination airport. Under those rules, how many miles does the [quoted text clipped - 4 lines] | | ;-) lol :) >> Airline "passenger miles" measure the distance between the starting >> airport [quoted text clipped - 5 lines] > > ;-) Oh goody, I can fly around the world for the price of a ticket from London to Paris. Not all that strange really, an ex-girlfriend of mine flew from Pittsburgh to London via Chicago, no extra cost. It was either that or wait. I agree with you about the shuttle. 3 miles in 3 weeks is a nice comfortable safe velocity. And the velocity of light from JPL Ca. to Cassini orbiting Saturn and back is zero too. No wonder Einstein screwed up. Androcles. > Safety is measured by passenger miles, the airline industries all agree > the more passenger miles there are the safer it is. [quoted text clipped - 5 lines] > Cars cost say $20,000, add insurance and fuel and maintenance, > call it $40 an hour. Makes me wonder how I ever afforded one. I There's some serious problems with your assumptions - a baby buggy typically lasts much more than two years. I think all 4 kids in our family used the same one, then it was passed on to friends - figure maybe 8 kids * 16 years. It's the same with cars - I did spend $20,000 on the truck, but it's now 13 1/2 years old. My current car cost under $7000: bought used and run for 2 years, so far.  Signaturederek >>>> <snip> >>>> [quoted text clipped - 31 lines] > Safety is measured by passenger miles, the airline industries all agree > the more passenger miles there are the safer it is. Not quite. Safety is measured in passenger miles per *death*. Not just passenger miles. If you look at just 'passenger miles', the automobile carries more passenger miles each year than aircraft. But there are also a lot more fatalities when traveling by car, so the number of passenger-miles per *death* is lower for automobile travel than air travel. > Besides, babies grow out of baby buggies faster than astronauts > grow out of shuttles, the attrition rate is enormous. A baby buggy [quoted text clipped - 6 lines] > Staying home is an even less safe form of transport. You get ZERO > passenger miles that way. Nonsense. Since you don't understand the safety rating, it is small wonder you are confused. daestrom >>>>> <snip> >>>>> [quoted text clipped - 38 lines] > passenger-miles per *death* is lower for automobile travel than air > travel. Ok... everyone dies. :-) >> Besides, babies grow out of baby buggies faster than astronauts >> grow out of shuttles, the attrition rate is enormous. A baby buggy [quoted text clipped - 11 lines] > > daestrom You are so f.cking dumb you don't know when someone is taking the piss. f.ck off, tord. *plonk* Androcles. >>>>>> <snip> >>>>>> [quoted text clipped - 61 lines] > *plonk* > Androcles. Ah, a typical response of the ignorant. Change the subject, throw vulgar insults around and leave. daestrom Androcles, I can almost always count on you to latch onto a more-or-less technical post and use it as an opportunity to expound upon something almost totally unrelated. Tom Davidson Richmond, VA Davidson, I can almost always count on you to latch onto a more-or-less technical post and fail to see a correlation (almost). Androcles. >> <snip> >> [quoted text clipped - 23 lines] > miles per hour. Shuttles are 30,000 times safer than baby buggies. > I don't know why young mothers put their children at risk like that. 'Passenger miles per hour' doesn't say anything about the relative safety of each mode of travel. Now, if you had calculated the number of deaths per passenger-mile, or number of deaths per passenger-hour, then we might have something to discuss. daestrom > <snip> > [quoted text clipped - 12 lines] > that don't get into the calculation, such as octane rating, speed, > headwind, engine rpm, and so on. cost of fuel... Signaturederek > Quoting from page 64 of Brit magazine _New Scientist_ dated 26 Feb > 2005 physical meaning of IQ expressed as an Area? Is it true that Brittian suffers an IQ shortage due to Mad Cow ? That could be and IQ of 50 per square mile. >> Quoting from page 64 of Brit magazine _New Scientist_ dated 26 Feb >> 2005 [quoted text clipped - 3 lines] > Is it true that Brittian suffers an IQ shortage due to Mad Cow ? > That could be and IQ of 50 per square mile. It might do, but at least we Britons can spell correctly! Britain an IQ WM > So does this fuel-efficiency expressed as an area have a physical > meaning? Is it the area under the curve of anything? No, it does not have any physical meaning. It would be like converting paint coverage Gal/sqft to a linear distance. Who would buy 500 ft of paint?! It would be like changing a Joule to a kg*m^2/s^3, which no longer makes sense. You loose a measurement's usefulness by unnecessarily reducing things down to base units. > > So does this fuel-efficiency expressed as an area have a physical > > meaning? Is it the area under the curve of anything? [quoted text clipped - 4 lines] > makes sense. You loose a measurement's usefulness by unnecessarily reducing > things down to base units. This is not a good example, as in fact there is a reasonable interpretation of the linear dimension gal/ft^2. That is, when you paint a wall you lay the paint on with some (rather small) thickness, over some (rather large) area; the product of these two is the volume of paint you used and the gal/ft^2 you mention is simply the thickness of the film of paint. Running with this idea, it's not even unreasonable to ask for 500 ft of paint, though actually, what you really want to do is ask for something like half a gallon of 0.001-ft paint: that is, paint which lays on one-thousandth of a foot thick, which in that quantity will paint 500 square feet of wall. It would actually be a good measure of the quality of the paint; you could get lots of "mileage" out of a really thin mixture but a nicer job from a thicker one. I'll agree with you on Joules, though. SignatureRyan Reich ryan.reich@gmail.com > > > So does this fuel-efficiency expressed as an area have a physical > > > meaning? Is it the area under the curve of anything? [quoted text clipped - 19 lines] > quality of the paint; you could get lots of "mileage" out of a really > thin mixture but a nicer job from a thicker one. To reply to myself, this probably works better if I replace "gallon" by "cubic foot", to which it is not equivalent. SignatureRyan Reich ryan.reich@gmail.com >> So does this fuel-efficiency expressed as an area have a physical >> meaning? Is it the area under the curve of anything? > > No, it does not have any physical meaning. It would be like converting > paint coverage Gal/sqft to a linear distance. Who would buy 500 ft of > paint?! You can't. Gal/sqft, or 'ft' is not a measure of how much paint you buy, it's how well the paint covers a surface. Just like you can't go into a store today and buy 1 gal/sqft. (see, you are talking about the rate of coverage, not the amount of paint). If I could by paint that covers at the rate of 500 ft, I'd buy it in a second. An average gallon of latex paint might cover 300 sqft, so an average latex paint normally covers at the rate of 0.00044 ft. To get 500 ft coverage from any kind of paint would be miraculous. But if I want to paint a 900 sqft wall with latex paint, I might multiply 900 sqft (area to be painted) * 0.00044 ft (rate of coverage) = 0.4 ft^3 of paint. Which works out to 3 gallons (the same as if I multiply 1 gal/300sqft * 900 sqft = 3 gal). > It would be like changing a Joule to a kg*m^2/s^3, which no longer makes > sense. The correct units for a Joule would be kg*m^2/s^2, not s^3. But interestingly, 1 watt (1 Joule/second) is equivalent to 1 kg*m^2/s^3. And that has very real meaning, and can make a lot of sense. Being able to move 3 kg a distance of 4 m (from a dead stop with constant acceleration) in 12 seconds would require a power level of 2 * 3kg * (4m)^2 / (12s)^3 = 0.05556 watts. Notice how the formula has kg*m^2/s^3 on one side of the equal sign and watts on the other?? > You loose a measurement's usefulness by unnecessarily reducing things down > to base units. Not really. You just loose a measurement's usefulness when you confuse what it is you're actually measuring and mucking up the units. (as you have here) daestrom >>> So does this fuel-efficiency expressed as an area have a physical >>> meaning? Is it the area under the curve of anything? [quoted text clipped - 12 lines] >average latex paint normally covers at the rate of 0.00044 ft. To get 500 >ft coverage from any kind of paint would be miraculous. Ahem. If you want to economize on paint bought, you want few gallons to cover many square feet, that is, you want paint for which the "gallons per square foot" measure is SMALL. Converting this unit to a linear quantity, as you have done, is OK by me but you still want the number in front of the unit to be small, not large. If you bought paint which has a "500ft" coverage rate, that would be paint that runs out a million times as rapidly as standard paints. In fact in this case, as with the automobile mileage example, the reduction to simpler units does have a natural interpretation: this linear quantity you calculate is just the thickness of the paint being lain down. (Assuming no change in volume as the paint dries, which I agree is sort of dubious.) All the more reason you don't want paint with a "500 ft" coverage rate... dave >>>> So does this fuel-efficiency expressed as an area have a physical >>>> meaning? Is it the area under the curve of anything? [quoted text clipped - 22 lines] > "500ft" coverage rate, that would be paint that runs out a million times > as rapidly as standard paints. You're right of course. Guess I confused it somewhere along the way with the inverse or something. daestrom > Is it the area under the curve of anything? That it is. It is the area under the constant function f(x)= GasMileage, where x is in [0,1]. > Quoting from page 64 of Brit magazine _New Scientist_ dated 26 Feb > 2005 [quoted text clipped - 17 lines] > So does this fuel-efficiency expressed as an area have a physical > meaning? Is it the area under the curve of anything? Let's be quite explicit here: Let's fill the gas tank full of gas, assume that the tank is rectangular, assume that the tank is oriented so one of its planes is horizontal, and the distance we drive is the distance we get when we exhaust the tank. The volume in the numerator is (tank width)x(tank height)x(tank depth). The distance in the denominator is (distance car goes) When you "cancel" one of the distances in the numerator with the distance in the denominator, you introduce a conversion factor. You can think of this number as "vertical inches of gas in tank per inch the car goes". In this case, the area remaining is the cross-sectional area of the gas tank. The problem is that the conversion factor number, the "vertical inches of gas per inch the car goes" will vary from car to car. It will in fact depend on the geometry of the tank, the performance of the engine, and the usual kind of thing. Because of the vast variation of this constant, the area you get out is not any kind of useful physical number that has any independent meaning. PD > Let's be quite explicit.... the area remaining is the cross-sectional area > of the gas tank. I select this reply as the most sensible & intuitively satisfying answer. > > Let's be quite explicit.... the area remaining is the cross-sectional area > > of the gas tank. > > I select this reply as the most sensible & intuitively satisfying > answer. I thought Michael Moroney's was the best /shrug SignatureLarry Lard Replies to group please > > > Let's be quite explicit.... the area remaining is the cross-sectional area > > > of the gas tank. [quoted text clipped - 3 lines] > > I thought Michael Moroney's was the best /shrug Now that you mention it, so do I. PD dances_with_barkadas wrote: > Quoting from page 64 of Brit magazine _New Scientist_ dated 26 Feb 2005 > > [reader Chris Bolton points out that fuel efficiency can be > expressed, not only as distance/volume (eg, miles/gallon) but also as > volume/distance (eg,] "liters/100 kilometers[ ) ]. But that's > length-cubed divided by length, which is an area. ... That neglects something very important. It's actually Distance traveled/Fuel consumed. The quantities are different. Simply cancel units is wrong. A unit "traveled" does not equal a unit "consumed". > dances_with_barkadas wrote: > [quoted text clipped - 10 lines] > Simply cancel units is wrong. A unit "traveled" does not equal a unit > "consumed". Right. In aviation, the unit for fuel is lbs. In engine terminology for any kind of IC engine there is a term called specific fuel consumption. This is the wieght of fuel consumed per horsepower per hour. Weight is what relates to the energy. The volume of fuel varies a bit due to temperature. Hydrocarbons have a given energy content per pound. > Right. In aviation, the unit for fuel is lbs. can you show me a dealer who sells aviation fuel by weight? > > Right. In aviation, the unit for fuel is lbs. > > can you show me a dealer who sells aviation fuel by weight? No. Only has to read a fuel pump where moneys are involved. "Volume corrected to 15C" > > > Right. In aviation, the unit for fuel is lbs. > > > > can you show me a dealer who sells aviation fuel by weight? > > No. > Only has to read a fuel pump where moneys are involved. > [quoted text clipped - 9 lines] > > > > No. ? Volume corrected because it is sold by weight. > > Only has to read a fuel pump where moneys are involved. > > > > "Volume corrected to 15C" > > > > > In article <1139107172.108544.116860@g14g2000cwa.googlegroups.com> > > > > > Right. In aviation, the unit for fuel is lbs. > > > > [quoted text clipped - 4 lines] > > ? > Volume corrected because it is sold by weight. Measured in mass (weight), then converted to volume by applying the sg of the fuel at 15 C. Displayed as volume for public comfort (and because fuel tank capacity is volume). surfnturf > Quoting from page 64 of Brit magazine _New Scientist_ dated 26 Feb > 2005 [quoted text clipped - 7 lines] > cross-sectional area of the continuous thread of fuel required to feed > the vehicle." You have to take everything from New Scienitist like all products of British Enginnering, though. It's not only archaic ---- it's Mideval --- it's French Archaic!!!! They should sell it to the Australians, they're the only people on Earth with 100.000 years of spare femto-seconds, and 100 Billion extra McDonald Quarter Pounds to waste on Britsh Newton Dooffi Maximi. > Well, I did think about it, trying to decide what is the physical > reality of that area. At first I thought it might be the area of the [quoted text clipped - 5 lines] > So does this fuel-efficiency expressed as an area have a physical > meaning? Is it the area under the curve of anything? |
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