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Natural Science Forum / Physics / General Physics / July 2007The magic of a Prius automobile
In an article today (7/23) the Raleigh NC News and Observer described how Prius owners were getting close to 50 mpg on the highway. See http://www.newsobserver.com/news/growth/traffic/gas/story/646209.html for details. Could someone here without a 'Green is Good' agenda explain in small words why a car hauling around extra batteries and an electric motor as weight should get better highway milage than a similar car not carrying around the extra weight? I can understand energy recovery and engine off stuff in city driving, but it seems to me the Green' arguement is misplaced here. Which leads to another question. For driving the stop and go nature makes a hybred a reasonable choice, but what about for those who live in small towns or suburbs? Is the milage claim real life meaningful, or bogus? > In an article today (7/23) the Raleigh NC News and Observer described > how Prius owners were getting close to 50 mpg on the highway. See > http://www.newsobserver.com/news/growth/traffic/gas/story/646209.html > for details. > Could someone here without a 'Green is Good' agenda explain in small > words why a car hauling around extra batteries and an electric motor > as weight should get better highway milage than a similar car not > carrying around the extra weight? > I can understand energy recovery and engine off stuff in city driving, > but it seems to me the Green' arguement is misplaced here. > Which leads to another question. For driving the stop and go nature > makes a hybred a reasonable choice, but what about for those who live > in small towns or suburbs? Is the milage claim real life meaningful, > or bogus? For extended trips at a constant speed, a hybrid is no better than a conventional vehicle of equivalent weight and engine size. How could it be otherwise if the electrics aren't even used? Now, if you live in hill country...  SignatureJim Pennino Remove .spam.sux to reply. > In an article today (7/23) the Raleigh NC News and Observer described > how Prius owners were getting close to 50 mpg on the highway. See [quoted text clipped - 7 lines] > as weight should get better highway milage than a similar car not > carrying around the extra weight? We recently completed a 1100 mile car trip in our 2007 Prius. With four people and quite a bit of luggage, we averaged 48 mpg for the entire trip. It's true that hybrids have the most benefit for city driving, but watching the energy recovery monitors drives home the fact that even driving on the highway, you change speed more than you think you do, and for a hybrid, taking advantage of this more than cancels out the rather slight increase in weight due to the batteries and electric motor. You're also forgetting the rather substantial effect that because the electric motor adds significantly to the torque, you're satisfied with a smaller gas engine than you would be if that were your only power, and that benefits you at all speeds. Yes, you could do better with with the same body and just a (wimpy) gas engine if you drove the 1100 miles at a constant velocity without stopping, but the authorities tend to frown on this, not to mention the fact that it makes eating and refeuling rather problematic. Toyota doesn't make a conventional Prius, but you can get some idea by comparing the traditional and hybrid Honda Civic, which get 40mpg and 51mpg highway, respectively. Again, this is due in part to the fact that the gas powerplant is larger in the conventional Civic than the Hybrid (140hp vs 110). -jc > > In an article today (7/23) the Raleigh NC News and Observer described > > how Prius owners were getting close to 50 mpg on the highway. See [quoted text clipped - 7 lines] > > as weight should get better highway milage than a similar car not > > carrying around the extra weight? > We recently completed a 1100 mile car trip in our 2007 Prius. > With four people and quite a bit of luggage, we averaged > 48 mpg for the entire trip. > It's true that hybrids have the most benefit for > city driving, but watching the energy recovery monitors [quoted text clipped - 3 lines] > than cancels out the rather slight increase in > weight due to the batteries and electric motor. When on the open highway and able to run at a constant speed, I turn on the cruise control and don't change speed at all. > You're also forgetting the rather substantial effect > that because the electric motor adds significantly > to the torque, you're satisfied with a smaller > gas engine than you would be if that were > your only power, and that benefits you at > all speeds. And that torque comes at a higher price than would a slightly larger gas engine. > Yes, you could do better with with the same body > and just a (wimpy) gas engine if you drove the 1100 miles > at a constant velocity without stopping, but the > authorities tend to frown on this, not to mention > the fact that it makes eating and refeuling rather > problematic. What "authorities" care how long I drive without stopping if there is no stop sign, light, etc.? > Toyota doesn't make a conventional Prius, but > you can get some idea by comparing the [quoted text clipped - 3 lines] > the gas powerplant is larger in the conventional > Civic than the Hybrid (140hp vs 110). And the gas cost difference for 100,000 miles of driving at $3.00/gal is about $1600 while the cars differ in MSRP by about $3k to $5k depending on model. The bottom line is there are a whole bunch of factors in determining whether or not a hybrid is a "good idea". SignatureJim Pennino Remove .spam.sux to reply. On Jul 23, 2:15 pm, j...@specsol.spam.sux.com wrote: > > > In an article today (7/23) the Raleigh NC News and Observer described > > > how Prius owners were getting close to 50 mpg on the highway. See [quoted text clipped - 21 lines] > When on the open highway and able to run at a constant speed, > I turn on the cruise control and don't change speed at all. This is possible in places like Nevada and Texas, but in most places, leaving the cruise control on all the time isn't possible because of traffic. Also, even with the cruise control on, at a constant velocity, hybrid cars make the engine more efficient over changing terrain (again, not a factor in Texas or much of Nevada). Hybrids get higher mileage on the highway, too - period. Sorry if that bothers you. > > You're also forgetting the rather substantial effect > > that because the electric motor adds significantly [quoted text clipped - 5 lines] > And that torque comes at a higher price than would a slightly > larger gas engine. And it's cheaper to burn your garbage than pay for trash service. Saving fuel is about more than money. > > Yes, you could do better with with the same body > > and just a (wimpy) gas engine if you drove the 1100 miles [quoted text clipped - 5 lines] > What "authorities" care how long I drive without stopping if there > is no stop sign, light, etc.? Turn your humor circuits on. Can you drive 1100 miles without stopping? > > Toyota doesn't make a conventional Prius, but > > you can get some idea by comparing the [quoted text clipped - 10 lines] > The bottom line is there are a whole bunch of factors in > determining whether or not a hybrid is a "good idea". As I said, I don't do it for the money. I do it to put less Carbon in the atmosphere and ship less money to stone age barbarians that want to kill me. -jc > -- > Jim Pennino > > Remove .spam.sux to reply. > On Jul 23, 2:15 pm, j...@specsol.spam.sux.com wrote: > > > > In an article today (7/23) the Raleigh NC News and Observer described [quoted text clipped - 22 lines] > > When on the open highway and able to run at a constant speed, > > I turn on the cruise control and don't change speed at all. > This is possible in places like Nevada and Texas, > but in most places, leaving the cruise > control on all the time isn't possible because of > traffic. Outside of metro areas and weekends on popular destination links such as LA to Vegas, open highway traffic tends to move at a constant speed. > Also, even with the cruise control on, at > a constant velocity, hybrid cars make > the engine more efficient over changing > terrain (again, not a factor in Texas or > much of Nevada). Or most of Arizona, New Mexico, Oklahoma, Kansas, Nebraska, South Dakota, North Dakota, Iowa, Missouri, Illinois, Indiana, Florida, eastern Montana. > Hybrids get higher mileage on the highway, too - period. > Sorry if that bothers you. Hybrids on the open highway get the same milage as a comperable weight and engine gas car. Sorry if that bothers you. They get better mileage if the traffic or terrain is variable. What bothers me is absolute statements that can be trivially shown to be false. > > > You're also forgetting the rather substantial effect > > > that because the electric motor adds significantly [quoted text clipped - 5 lines] > > And that torque comes at a higher price than would a slightly > > larger gas engine. > And it's cheaper to burn your garbage than pay for > trash service. Saving fuel is about more than > money. If that is what is important to you. > > > Yes, you could do better with with the same body > > > and just a (wimpy) gas engine if you drove the 1100 miles [quoted text clipped - 5 lines] > > What "authorities" care how long I drive without stopping if there > > is no stop sign, light, etc.? > Turn your humor circuits on. Can you drive 1100 miles > without stopping? Not without some up-front work. My best so far is a bit short of 500 miles, though I was a LOT younger then. > > > Toyota doesn't make a conventional Prius, but > > > you can get some idea by comparing the [quoted text clipped - 10 lines] > > The bottom line is there are a whole bunch of factors in > > determining whether or not a hybrid is a "good idea". > As I said, I don't do it for the money. I do it to put less > Carbon in the atmosphere and ship less money to > stone age barbarians that want to kill me. The top 4 US oil imports come from Canada, Saudi Arabia, Mexico, and Venezuela, in that order. The following 11, with less that 1 million barrels per day are Nigeria, Angola, Algeria, Iraq, Russia, Ecuador, United Kingdom, Huwait, Brazil Norway, and Brazzaville. I hadn't realized Canada had stone age barbarians that want to kill me. I guess I'll stop drinking their beer then. SignatureJim Pennino Remove .spam.sux to reply. On Jul 24, 10:55 am, j...@specsol.spam.sux.com wrote: > > On Jul 23, 2:15 pm, j...@specsol.spam.sux.com wrote: > > > > > In an article today (7/23) the Raleigh NC News and Observer described [quoted text clipped - 49 lines] > > Sorry if that bothers you. Maybe you can remind me which non-hybrid cars get 48 mpg at 60-70 mph with four adult sized passengers and their luggage. Personally, I can't think of any. -jc > They get better mileage if the traffic or terrain is variable. > [quoted text clipped - 66 lines] > > Remove .spam.sux to reply. > On Jul 24, 10:55 am, j...@specsol.spam.sux.com wrote: > > > On Jul 23, 2:15 pm, j...@specsol.spam.sux.com wrote: [quoted text clipped - 50 lines] > > > > Sorry if that bothers you. > Maybe you can remind me which non-hybrid cars > get 48 mpg at 60-70 mph with four adult sized > passengers and their luggage. Personally, > I can't think of any. Real world reports from drivers in other reports in this thread report 38-61 mpg on the highway, depending on conditions. Do I get the same range? Current models or for all time? Are you a Toyota salesman or are you just one of those people who get their panties all in a wad if they feel someone is dissing one of their prized possessions? Personally, I could give a rat's a.s less. The decision on which car I'll buy next is going to be based on total cost of ownership and suitablility of purpose within my set of circumstances, which means it may not even be a "car". SignatureJim Pennino Remove .spam.sux to reply. On Jul 25, 6:35 pm, j...@specsol.spam.sux.com wrote: > > On Jul 24, 10:55 am, j...@specsol.spam.sux.com wrote: > > > > On Jul 23, 2:15 pm, j...@specsol.spam.sux.com wrote: [quoted text clipped - 62 lines] > > Current models or for all time? I'll take that as a "no". > Are you a Toyota salesman or are you just one of those people who get > their panties all in a wad if they feel someone is dissing one of their > prized possessions? No. You started this thread by stating that anyone who claimed that hybrids got better highway mileage was essentially lying or deluded. That statement is contradicted both by witnesses and the EPA data. When asked to back up your claims, you resorted to insults rather than facts. > Personally, I could give a rat's a.s less. > > The decision on which car I'll buy next is going to be based on total > cost of ownership and suitablility of purpose within my set of > circumstances, which means it may not even be a "car". Nice, but it has nothing to do with the issue at hand. -jc > -- > Jim Pennino > > Remove .spam.sux to reply. > On Jul 25, 6:35 pm, j...@specsol.spam.sux.com wrote: > > > On Jul 24, 10:55 am, j...@specsol.spam.sux.com wrote: [quoted text clipped - 63 lines] > > > > Current models or for all time? > I'll take that as a "no". No to what? > > Are you a Toyota salesman or are you just one of those people who get > > their panties all in a wad if they feel someone is dissing one of their > > prized possessions? > No. You started this thread by stating that anyone who claimed > that hybrids got better highway mileage was essentially lying > or deluded. That statement is contradicted both by witnesses > and the EPA data. Paranoid nonsense. The worst thing I said about the Prius is that on the flat, open highway it gets mileage comparable to an ordinary car of the same weight and engine size. And the reports from owners would seem to back that up. So what's your problem? > When asked to back up your claims, you resorted to insults > rather than facts. Sorry if you feel insulted, I didn't realize you were a member of the holy church of the Prius, praised be its name. There is no need for me to back up the claim; owners already have. > > Personally, I could give a rat's a.s less. > > > > The decision on which car I'll buy next is going to be based on total > > cost of ownership and suitablility of purpose within my set of > > circumstances, which means it may not even be a "car". > Nice, but it has nothing to do with the issue at hand. Which is what exactly? That under some conditions hybrids get great mileage and under some other conditions there is little to no difference? If it works for you, great, huzzah, good choice, more power to you. SignatureJim Pennino Remove .spam.sux to reply. > In an article today (7/23) the Raleigh NC News and Observer described > how Prius owners were getting close to 50 mpg on the highway. See [quoted text clipped - 15 lines] > in small towns or suburbs? Is the milage claim real life meaningful, > or bogus? I belong to a car-sharing program in Philadelphia and when I borrow a car from the program, I always take a Prius (originally that's all they had, but they've since expanded the fleet). I drive it in the city and on the nearby suburbs and highways, and my experience is that I get about the same mileage, around 43 mpg, in both environments. So I wouldn't claim it's bogus. Unfortunately, I don't typically look at the energy usage display which shows when the electric or gas engine is being used, and whether energy is flowing into or out of the batteries. Next time I take it out, I'll use that display. I tend to use a summary mpg display. That feedback does tend to train you in good habits. Nothing like seeing your instantaneous mileage go down from 42 to 20 to make you get your foot off the accelerator. The main good habit that gets me those numbers outside of the city is to coast when going downhill, which seems to more than make up for the cost of going uphill. Strangely, I don't think the mileage would be nearly as good on level ground. Could you get the same kind of mileage with the same habits in a conventional car? Don't know. My usual car is a 2001 Corolla, and on the same route with the same habits, the best I can achieve seems to be about 33.5 - Randy > > In an article today (7/23) the Raleigh NC News and Observer described > > how Prius owners were getting close to 50 mpg on the highway. See [quoted text clipped - 32 lines] > instantaneous mileage go down from 42 to 20 to make you > get your foot off the accelerator. Note that it's not so much the accelerator, as the brake that matters. The extra energy burned during acceleration isn't necessarily wasted. Many (most?) engines actually run more efficiently with the throttle wider open. If you're accelerating up to cruising speed, then rapid acceleration isn't wasteful; however if you're just going a short distance to the next stop sign, the extra energy put into speed is quickly discarded when you hit the brakes. Drive in a manner that minimizes brake usage in order to get better mileage. Paul Cardinale > I tend to use a summary mpg display. That feedback does > tend to train you in good habits. Nothing like seeing your > instantaneous mileage go down from 42 to 20 to make you > get your foot off the accelerator. ITYM, lighten your foot on the accelerator. Note that for conventional engines this ends up costing more fuel overall: if you drive to minimise your mpg at any instant, it does not minimise the overall fuel consumption. In fact you get the best average mpg by accelerating briskly to your target speed. (Try it). The reason for this is that conventional engines are the most thermally efficient with a free air-flow (i.e. open throttle) and in the middle of their RPM range, and least efficient when they have to suck air around the side of an almost-closed throttle plate. The thermal efficiency reflects how much of the energy stored in the fuel gets translated to kinetic energy. (Note the caveat that at fully open throttle, most engine computers change the timing for greater power and less efficiency, so for the most efficient acceleration you should use a nearly, but not fully, open throttle). Having said that, I'm not sure how much of this applies to hybrid engines, since I don't know when and how they use their two engines. A secondary concern, which applies to both hybrids and conventional engines, is that slow acceleration impairs the flow of traffic, which results in more people waiting at traffic lights or in traffic jams. Any gains you might get from slotheration, you lose due to the increased traffic congestion caused. Or should I say, the non-hybrid cars caught up in the congestion lose because they all have to do extra idling or creeping along at idle speeds, getting basically 0 mpg. I find it ironic that the anti-GW brigade promotes driving slowly, an action that directly leads to greater traffic congestion and thus a far higher total output of CO2 as well as other harmful emissions (closed throttle = car not breathing = poor combustion = side products like CO). : > I tend to use a summary mpg display. That feedback does : > tend to train you in good habits. Nothing like seeing your [quoted text clipped - 7 lines] : consumption. In fact you get the best average mpg : by accelerating briskly to your target speed. (Try it). In fact you get the best average mpg by reducing air friction. In fact if you drive to minimise your mpg at any instant, it DOES minimise the overall fuel consumption. Drive slowly. (Try it). You don't seem to know what a fact is, but it is a fact that less fuel is used per mile at low speed than at high speed, because E = 1/2 mv^2. The faster you go, the more energy is needed. In fact. There is some speed at which the Prius gets best milage, I'd guess it's in the 40 mph range, but does anyone know factually? The 'slower is better' arguement does fail at slower speeds -- air resistance goes as more or less the square of velocity, the 'hotel load' on the engine is fixed, and the little engine's efficiency curve has a maximum somewhere. > : > I tend to use a summary mpg display. That feedback does > : > tend to train you in good habits. Nothing like seeing your [quoted text clipped - 15 lines] > because E = 1/2 mv^2. > The faster you go, the more energy is needed. In fact. : There is some speed at which the Prius gets best milage, I'd guess : it's in the 40 mph range, but does anyone know factually? The 'slower : is better' arguement does fail at slower speeds -- air resistance goes : as more or less the square of velocity, the 'hotel load' on the engine : is fixed, and the little engine's efficiency curve has a maximum : somewhere. You can guess as much as you like, the laws of physics don't change. An engine's efficiency is its useful energy out divided by energy in times 100 and speed has nothing to do wiith it. Most internal combustion engines are around 18% efficient, the remaining 82% is lost as heat. Power stations are typically 33% efficient and that is mainly because they have larger "engines" (turbines) than little sliding piston pumpers which lose a lot of heat to friction but are more expensive to build. Which would be more "efficient", a large truck hauling 32 tons one mile up a steep grade or 32 small cars hauling one ton each? The truck, obviously. And it costs less, that's why we use them. Railways were effective because the routes chosen didn't go over hills and valleys, the steam engine itself was extremely inefficient and grossly underpowered, so although you can carry many tons by rail you can't do it uphill. That leaves air resistance as the deciding factor. Energy is a function of fuel. Go as fast as you like downhill with the engine off but you'll still encounter air resistance, that's why aircraft are streamlined. Land yachts travel without fuel but are not much use for hauling heavy loads or hill climbing. Landyacht World Speed Record Current record of 116.7 mph was set 3/20/99 by 'Iron Duck' Source: http://www.sevenravens.com/landsailing/ : > : > I tend to use a summary mpg display. That feedback does : > : > tend to train you in good habits. Nothing like seeing your [quoted text clipped - 15 lines] : > because E = 1/2 mv^2. : > The faster you go, the more energy is needed. In fact. > There is some speed at which the Prius gets best milage, I'd guess > it's in the 40 mph range, but does anyone know factually? The 'slower > is better' arguement does fail at slower speeds -- air resistance goes > as more or less the square of velocity, the 'hotel load' on the engine > is fixed, and the little engine's efficiency curve has a maximum > somewhere. On a calm warm day, I got 62 mph from Ames to the Des Moines Airport (one way) once this summer with the majority of the trip down being at 65 mph... The round trip average was 56 mpg. And that was with the headlight and AC on. Typically such a trip renders closer to 50-52 mph. Year ago in January, on a trip back to Ames from the Twin Cities with a 20 mph head wind, I couldn't do better than 36 mpg! Under the right conditions of wind, temperature, no rain and tire ware, performance can be mind bobbling. Other times very frustrating. Wind and temperature are the biggest factors. > In fact if you drive to minimise your mpg at any instant, it DOES > minimise the overall fuel consumption. Drive slowly. (Try it). > You don't seem to know what a fact is, but it is a fact that > less fuel is used per mile at low speed than at high speed, > because E = 1/2 mv^2. > The faster you go, the more energy is needed. In fact. What I said was: if your goal is to accelerate to a certain speed (let's say 50mph), you use less fuel (per distance covered) by accelerating briskly to 50, than by accelerating slowly to 50. : > In fact if you drive to minimise your mpg at any instant, it DOES : > minimise the overall fuel consumption. Drive slowly. (Try it). [quoted text clipped - 7 lines] : less fuel (per distance covered) by accelerating : briskly to 50, than by accelerating slowly to 50. Perhaps you can point out in the message below to where you said that, I must have missed it. Even then the energy required is the same regardless of acceleration, although as a practical matter there would be a trade-off between the air friction and the internal friction of the car. A greater acceleration would involve higher engine RPM as the vehicle is held in low gear longer. The maximum acceleration you can obtain, as with the maximum braking, is when the tyre starts to slide on the road surface leaving skid marks. Vehicles today are equipped with automatic braking systems (ABS) designed to prevent that happening. You'll use more fuel overcoming internal friction resistance than air resistance at low velocities, but at higher velocities the reverse is true. As a rough guide, consider that the internal resistance is more or less constant (in top gear) but air resistance increases with velocity. You have only to put your hand out of the window to feel the force, and then multiply that by the area of the windshield and divide by the area of your hand to realise it is considerably large. As to the hybrid: Toyota describes HSD-equipped vehicles as having E-CVT (Electronically-controlled Continuously Variable Transmission). If you understand a differential transmission (animated here: http://www.androcles01.pwp.blueyonder.co.uk/Differential.gif ) then consider running it in reverse, i.e. turn the wheels to drive the mainshaft rather than turning the shaft to drive the wheels, then a constant RPM internal combustion engine and a variable speed electric motor replacing the wheels will vary the speed of the mainshaft which can then drive another differential (not shown). If the mainshaft is held stationary then any rotation of the half shaft produces a counter rotation in the other half shaft, the motor becomes a generator and the engine can charge the batteries. So for in-town driving, stop the engine and run on the motor only. Advantage: No gas emissions, quiet, smooth running. For highways, run the engine and also recharge the batteries. Hook in a computer to do the controlling and that's all there is to it. You get the added bonus of recharging the batteries when the car runs downhill, energy recovered that would otherwise be lost as heat in the brakes. You then use that to assist in going up-hill. Advantage: energy is conserved, high mpg. Disadvantage: Higher initial cost, extra weight of batteries, expensive maintenance requiring specialist knowledge. Mechanics have to be re-trained in electrical systems. Americans are in love with big powerful engines with lots of acceleration, although they don't drive all that fast. They are also patriotic (and parochial), notice their love of Harley-Davidson motorcycles, a machine that for years was inferior to Japanese products. Only when Ford, GM and Chrysler develop the hybrid will it have any significant popularity. As an aside, arguing with Blind Poe is futile. He believes a bus cannot stop in the same distance as a car from the same initial velocity because his government has decreed it. His knowledge of physics and his reasoning powers betray an intelligence in two figures only, he believes what authority tells him. A bus takes longer to stop than a car because the driver is courteous to his standing passengers who are about to disembark the vehicle and not for any physical reason. Blind Poe will use that as argument without disclosing the reason for it. In other words he's an idiot troll and all-round bigot who cannot tolerate being proven wrong. You'll find many just like him. I find it ironic that the GW brigade actually believes CO2 emissions have any impact whatsoever on the axial precession of Earth in relation to its perihelion, but if they are right then Neanderthals must have been charging around in 4x4s and SUVs 130,000 years ago when the last warming took place. http://www.roperld.com/graphics/LIAInsolation.jpg We'll just have to be ironic at each other. ----- Original Message ----- From: "Old Wolf" <oldwolf@inspire.net.nz> Newsgroups: sci.physics Sent: Tuesday, July 24, 2007 4:02 AM Subject: Re: The magic of a Prius automobile : On Jul 24, 5:11 am, Randy Poe <poespam-t...@yahoo.com> wrote: : > I tend to use a summary mpg display. That feedback does [quoted text clipped - 46 lines] : emissions (closed throttle = car not breathing : = poor combustion = side products like CO). > As an aside, arguing with Blind Poe is futile. He believes a bus > cannot stop in the same distance as a car from the same initial [quoted text clipped - 7 lines] > other words he's an idiot troll and all-round bigot who cannot > tolerate being proven wrong. You'll find many just like him. Hmm, who would collect actual data on stopping distances of vehicles? Well, it seems that government departments of transportation would be a reasonable source, since that falls under their charter. But wait! You decided that any publication from a goverment DOT is automatically wrong by being from a government. Hence the only reliable source of data you trust is data pulled from your a.s. I can only counter a.s-data with measured data, and you've dismissed all the measured data. So I guess in your world that means you win. I guess you win the argument on the human vision system too, since the theory of human vision pulled from your rectum is automatically superior to the medical school anatomy articles I provided you. And I guess argumentum ab rectum Androclou [1] beats actual data on relativity too. What can I say, Androcles. Your arguments are invincible. - Randy [1] An attempt at a Greek genitive :-) : > As an aside, arguing with Blind Poe is futile. He believes a bus : > cannot stop in the same distance as a car from the same initial [quoted text clipped - 10 lines] : Hmm, who would collect actual data on stopping distances : of vehicles? Goodyear, Michelin, Dunlop...most tyre manufacturers, they provide the necessary equipment. Then there would be Ferodo... Founded in England in 1897, Ferodo was the first company in the world to be entirely dedicated to the design and manufacture of friction products. And of course Ford, GM, Volvo... A bus takes longer to stop than a car because the driver is courteous to his standing passengers who are about to disembark the vehicle and NOT for any physical reason. Blind Poe will use that as argument without disclosing the reason for it. In other words he's an idiot troll and all-round bigot who cannot tolerate being proven wrong. His knowledge of physics and his reasoning powers betray an intelligence in two figures only, he believes what authority tells him. : Well, it seems that government departments : of transportation would be a reasonable source, since that : falls under their charter. Good argument, "seems". It means ignore the facts and make assumptions. : But wait! Yes, Blind Poe, let's wait. You are about to lie. : You decided that any publication from a goverment : DOT is automatically wrong by being from a government. The accusation is that I have decided ANY publication from a government DOT is automatically wrong. I plead not guilty, I have neither made nor declared such a decision. Now we'll wait and see you prove your allegation, you seemingly LYING tord. We'll have to wait a long time. > As an aside, arguing with Blind Poe is futile. He believes a bus > cannot stop in the same distance as a car from the same initial [quoted text clipped - 7 lines] > other words he's an idiot troll and all-round bigot who cannot > tolerate being proven wrong. You'll find many just like him. Well, it's futile since numbers from Androcles' butt always beat numbers from measured data, but what the hell, some actual numbers: http://www.thsao.on.ca/docs/winter_tips.pdf "Remember, a loaded bus traveling at 90km/h requires approximately 126 metres (390 feet) of stopping distance in ideal conditions. A loaded tractor-trailer at 90 km/h will need approximately 171 metres (520 feet) of stopping distance in ideal conditions." In contrast, the stopping distance for a car at 60 mph (96 kph) is 180 feet, or 312 feet if you include reaction time. http://www.arachnoid.com/lutusp/auto.html - Randy : > As an aside, arguing with Blind Poe is futile. He believes a bus : > cannot stop in the same distance as a car from the same initial [quoted text clipped - 14 lines] : http://www.thsao.on.ca/docs/winter_tips.pdf : "Remember, a loaded bus traveling at 90km/h requires approximately Approximately, fuckhead? : 126 metres (390 feet) of stopping distance in ideal conditions. A : loaded tractor-trailer at 90 km/h will need approximately 171 metres : (520 feet) of stopping distance in ideal conditions." Does mass make a difference, sh.t-for-brains? : In contrast, the stopping distance for a car at 60 mph (96 kph) : is 180 feet, Exact now, huh? No "approximately" anymore? : or 312 feet if you include reaction time. So reaction time is (312-180) feet * 88 fps = 1.5 seconds. Rather a long time to put your foot on the brake when a kiddy runs out in the road, Blind Poe. It's time you gave up driving if that's your reaction time. I doubt anyone would let you drive a bus, you couldn't even pass a regular test in a car. Now my reaction time is approximately a fifth of that, 300 milliseconds, and so is it for most other people. Your figures are approximately 500% in error. That's usual for government work. Approximate numbers beaten by measured data was easily done. : http://www.arachnoid.com/lutusp/auto.html Quoting some prat's website that says e: = mv^2 shows just how blind you are, Blind Poe. One of your students, was he? > "Old Wolf" <oldw...@inspire.net.nz> wrote in message > [quoted text clipped - 4 lines] > : > Even then the energy required is the same regardless of acceleration, Therefore, (ignoring friction for the moment), the least fuel is used by operating the engine in the mode where it's most thermally efficient. For most engines, as far as I know, this occurs with mostly open throttles and in the middle of the designated RPM range. > although as a practical matter there would be a trade-off between > the air friction and the internal friction of the car. A greater > acceleration would involve higher engine RPM as the vehicle is > held in low gear longer. I suppose you would also have to figure transmission losses into it; perhaps they are more or less efficient depending on the RPM as well. > The maximum acceleration you can obtain, > as with the maximum braking, is when the tyre starts to slide on > the road surface leaving skid marks. Vehicles today are equipped > with automatic braking systems (ABS) designed to prevent that > happening. The A in ABS stands for anti-lock, and it only applies to braking. The equivalent for acceleration is called traction control (or whatever trendy name the sales department came up with now). > You'll use more fuel overcoming internal friction resistance than > air resistance at low velocities, but at higher velocities the reverse [quoted text clipped - 4 lines] > and divide by the area of your hand to realise it is considerably > large. I suppose the question is: does the loss due to spending a higher proportion of the journey at the higher speed, exceed the gain due to thermally efficient acceleration? For low speeds (e.g. 40mph or less) the air resistance would not be significant. > He believes a bus cannot stop in the same distance as a car > from the same initial velocity because his government has decreed it Well, it seems to me that it depends on the heat dissipation rate of the brakes, and the grip of the tyres of each vehicle. I've seen heavily laden coal trucks stop in a damn hurry, so I don't see why buses couldn't do the same. Of course, many buses in service are old and have appalling brakes. : > "Old Wolf" <oldw...@inspire.net.nz> wrote in message : > [quoted text clipped - 11 lines] : open throttles and in the middle of the designated : RPM range. It would be very convenient to your argument to ignore friction for the moment, but inserting impossible caveats into the discussion isn't going to enlighten anyone. An engine is designed to do work, converting chemical energy to mechanical energy. Inevitably there are losses in the form of heat. For motor vehicles, all energy is eventually lost as heat in braking. If you are going to operate the engine at full throttle, get a small engine and do not accelerate as greatly, you will save fuel. Hence the term "gas guzzler" applies to vehicles with larger engines. : > although as a practical matter there would be a trade-off between : > the air friction and the internal friction of the car. A greater [quoted text clipped - 4 lines] : losses into it; perhaps they are more or less efficient : depending on the RPM as well. Yes indeed. Automatic transmissions have oil coolers in larger vehicles. The lower the gear, the greater the loss as heat. Manually operated clutches also run hotter at higher engine RPM, so again keep the RPM low and the gear ratio low, 1:1 is better than overdrive. That equates to low acceleration. Your argument for high acceleration is time related. It seems intuitive that one does not need to burn the fuel for as long a period of time, but the quantity of fuel increases. There is no overall fuel saving. Those old steam engines didn't need a gear box, the piston could move slowly. The internal combustion engine burns its fuel in a short time interval, typically running at ~2000 RPM = 33 revolutions per second. In a piston engine that's 66 strokes, one up and one down and takes 1/66 = 15 milliseconds to complete the burn. If the burn takes longer then the exhaust valve opens and unburnt fuel is wasted. If it takes less time then it is doing no useful work, waiting around for the valve to open and be expelled, and so the internal combustion engine has a short range of RPM in which it is efficient and that produces the need for careful ignition timing and a gearbox. Higher octane fuels can mean higher RPM but are more expensive to produce. Of course "good mileage" really equates to "low cost", and so we use cheaper fuel. : > The maximum acceleration you can obtain, : > as with the maximum braking, is when the tyre starts to slide on [quoted text clipped - 6 lines] : traction control (or whatever trendy name the sales : department came up with now). Then it should be ALBS, not ABS, but I agree its just a marketing ploy. All I'm saying is you don't accelerate as well by spinning your wheels, which, without locking the differential, will occur on one wheel only and the car will turn sideways. : > You'll use more fuel overcoming internal friction resistance than : > air resistance at low velocities, but at higher velocities the reverse [quoted text clipped - 11 lines] : For low speeds (e.g. 40mph or less) the air resistance : would not be significant. But it is significant. ALL the energy not lost as heat or used in climbing hills (where it can be recovered by rollng down them) is used to overcome air resistance. E = 1/2m v^2... Let m = 2 (the mass of the car is constant), so that E = v^2 At 10 mph, E = 100. At 20 mph, E = 400. At 30 mph, E = 900. At 40 mph, E = 1600. At 50 mph, E = 2500. At 60 mph, E = 3600. You need 4 times the fuel to get to 40 mph as you need to get to 20 mph, not twice as much, and if you then have to brake at a red light you've wasted it. We all do it, I know, we are all in a hurry, but we are not being economical. In practise, of course, nobody checks fuel mileage at 10 mph and there would be higher losses due to internal friction, heating and/or airconditioning, but accelerate gently and brake gently. To the truck owner it's a careful balance between paying for the driver's time, on-time delivery and fuel costs. A late delivery means the customer loses money paying idle hands, an early delivery and the driver is waiting around to be unloaded. : > He believes a bus cannot stop in the same distance as a car : > from the same initial velocity because his government has decreed it [quoted text clipped - 5 lines] : so I don't see why buses couldn't do the same. Of course, : many buses in service are old and have appalling brakes. Those are special cases, the physics of the situation is that a bus has a greater footprint on the road surface than a car, the emergency stopping distances are the same, all else being equal. We do not put 13" wheels on a bus, but we give it a proportionally smaller engine (7 litres typical for a London double decker). If a child runs out in front of the vehicle, the bus can stop as quickly as the car. It is a myth that the heavier vehicle will take longer to stop, a 400 ton airliner can stop as quickly as any car can from the same velocity and faster than a kid on a skateboard (which has no brakes) but not as quickly as a running man. I raced against my 5 litre Camaro once and won for several yards, my acceleration was greater initially but I could not sustain it, I'd reached my top speed of 15 mph in two or three strides. Stopping is more difficult, I almost fell. A large oil tanker on water takes longer to stop than a rowboat, but that's an almost frictionless surface and different conditions entirely. Put proportionally small screws on the rowing boat and then make the comparison. > > In an article today (7/23) the Raleigh NC News and Observer described > > how Prius owners were getting close to 50 mpg on the highway. See [quoted text clipped - 27 lines] > used, and whether energy is flowing into or out of the batteries. > Next time I take it out, I'll use that display. What kind of a geek are you??? That's the whole reason to buy the car :) -jc I tend to use a summary mpg display. That feedback does > tend to train you in good habits. Nothing like seeing your > instantaneous mileage go down from 42 to 20 to make you [quoted text clipped - 10 lines] > > - Randy > > Unfortunately, I don't typically look at the energy usage > > display which shows when the electric or gas engine is being [quoted text clipped - 3 lines] > What kind of a geek are you??? That's the whole reason > to buy the car :) I like the little summary graphs and I like driving the average figure up over time. :-) Anyway, I had one out today and looked at the other display. I noticed that in some circumstances where I would have thought the energy was coming strictly from the gasoline engine, it showed it coming from both electric and gasoline motors. I had at one point a steady mileage of 61 mpg on approximately level ground because of this sort of electric assist. I'm not sure the circumstances where that happens. - Randy > In an article today (7/23) the Raleigh NC News and Observer described > how Prius owners were getting close to 50 mpg on the highway. See [quoted text clipped - 15 lines] > in small towns or suburbs? Is the milage claim real life meaningful, > or bogus? My 2005 Prius Since April 2007 Date Odometer Gallons mpg Gas mpg Calc 2.61 070402 026844.0 08.297 45.558 Octane 87 47.0 2.79 070413 027170.0 07.112 45.838 Octane 87 2.72 070415 027526.0 07.701 46.227 Octane 87 50.1 2.74 070423 027866.0 07.139 47.625 Octane 87 48.6 2.94 070430 028301.0 09.300 46.774 Octane 87 50.8 3.30 070526 028721.0 08.444 49.739 Octane 87 48.3 3.16 070605 029156.0 08.633 50.388 Octane 87 53.3 3.00 070627 029595.0 08.883 49.420 Octane 87 2.95 070703 030126.0 09.497 55.912 Octane 87 54.0 3.27 070711 030397.0 06.321 42.872 Octane 87 Strong Wind 3.10 070720 030857.0 09.686 47.491 Octane 87 51.5 > Which leads to another question. For driving the stop and go nature > makes a hybred a reasonable choice, but what about for those who live > in small towns or suburbs? Is the milage claim real life meaningful, > or bogus? It's real all right. I commute in a '07 Prius from Santa Cruz to San Jose CA over the Santa Cruz mountains and get 49 MPG. Nearly all of that is twisty, hilly, moderately high speed highway. On the flat 80 MPH round trip between San Jose and San Francisco airport it drops precipitously to 47 MPG due to the 20 MPH higher speed. I can hardly believe it either. The drive switching is flawless. I can't find anything to criticize about this car and for me that is really unusual. The most amazing thing about it is the amount of torque it musters on request. No problem *at all* passing, ramp merging or just screwing around on mountain roads (including deflating the macho of Mexican boys in their pimped out Black Honda Civics.) Requesting torque does take a big toll on fuel usage but I wouldn't expect otherwise. Bob Signature"Things should be described as simply as possible, but no simpler." A. Einstein > In an article today (7/23) the Raleigh NC News and Observer described > how Prius owners were getting close to 50 mpg on the highway. See [quoted text clipped - 7 lines] > as weight should get better highway milage than a similar car not > carrying around the extra weight? You can get 50 mpg pretty easily at highway speeds with very small gas engines but you wouldn't want to drive one because your 0-60 time would be so long as to put you to sleep, not to mention your 60-80 time. You'd be a hazard merging from an on ramp unless there was a half mile traffic gap to match speeds. You wouldn't want to pass at 60 unless you had a mile to accomplish it. What the hybrid does is allow you to use such an unacceptably small gas motor to get the mileage and, for the magic, adds the electric motor to give you more than acceptable on-demand torque. Small electric motors can give remarkable torque for brief periods, limited mainly by the internal resistance of the battery. It's a very synergistic combination. Bob Signature"Things should be described as simply as possible, but no simpler." A. Einstein Bob and otheres, thanks. You all helped my understanding of the technology. > > In an article today (7/23) the Raleigh NC News and Observer described > > how Prius owners were getting close to 50 mpg on the highway. See [quoted text clipped - 26 lines] > > A. Einstein |
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