At open throttle, you *can* shift lower than you otherwise could. If, however, you're not accellerating that hard, it's another story.
Accelerating hard or under load (going up a hill, or carrying weight). Which of course leads to the wonderful fact that the best gas mileage for many trucks is obtained when going through hilly country. Since you don't use that much extra fuel to move up the hill (since you throttle less), the energy you store can improve your gas mileage when you come down. For large-engined vehicles, this can be a *huge* deal (difference between 20 and 30 mpg, in some cases).
For small cars, though, hills can hurt gas mileage. It's things like this that make me really ticked off at the EPA regarding gas mileage. Don't spread complete crap to people, just tell them the truth.
They just silently changed it, causing shitloads of confusion along the way. Of all the alternatives in this mess, they choose the one which could ruin an engineers day, only for the purpose of having your drive look a few % larger.
Silently? On all the hard drives I had for a long time, they specifically state what a MB (or GB) was - one billion bytes.
Honestly, it's fairly retarded to have to define what a standard is when you're using it.
You do realize, though, that you're complaining that they violated a convention to follow a standard, right? Standards are far more useful than conventions, because a standard is rigidly defined.
This isn't just hard drive manufacturers, either. Theoretical data rate is often expressed in MB/s, because it's just transfer frequency times payload size. Hell, you can figure out rough hard drive capacity by bit density times area.
The only place where binary prefixes are useful is for memory. The only place.
I mean, jeez. The computing industry doesn't even agree on the right case on the prefix (kilo is a lowercase k, not uppercase). We haven't been consistent. This wasn't because of marketing people, it was because we were sloppy. Whoever pointed it out to us, it's our own fault. Own up, and fix it. kB = 1000 bytes. KiB (note the uppercase!) is 1024 bytes. At least now there's a standard. It's one freaking letter.
Your hard drive uses something other than binary to address the data stored on it?
Yah, LBA (logical block addressing). You ask the drive "give me block X", and it gives you block X. No binary involved. The fact that the numbers are transmitted over binary is unimportant. It could've been done over ternary, or avian squawkspeak consisting of fifteen symbols.
"Binary addressing" means "addressed by a bunch of address lines which hold values in binary". So a 1024-byte SRAM has 10 address lines. If I want to add more capacity, I have to add another address line, which gives me 2048 bytes. In other words, memory sizes are 2^N, where N is the number of address lines. Here, it does matter that the address is transmitted via binary: if each address line held 3 states, the total memory size would be 3^N, not 2^N.
Note that most modern memory multiplex the address lines (as having 30 address lines for a gigabyte of memory is awkward) into row and column addresses, but it's still binary addressing, and memory sizes still need to scale by powers of 2.
Under standard PCI the host bus has a maximum speed of 66 MHz. This allows for a maximum transfer rate of 533 MB/sec across a 64-bit PCI bus.
66 (2/3) MHz times 8-bytes wide is 533 (1/3) MB/s. Here mega means 10^6, not 2^20. If it were megabinary, it'd be 508-something MiB/s. (*)
Look, computer usage of kilo has always sucked and been inconsistent. Always. Own up to it and fix it.
(*: I find it amusing that in order to find an example, I had to find one where they used "66 MHz" incorrectly, but no one actually writes 66.66... MHz, so forgive the irony.)
"1024 except for metrics being stated in bits or hertz"
So a 2 GHz link that's 1 byte wide transfers data at 1.862 GB/s? This is just silly.
As I argued in more depth elsewhere, anyone who used computers *knew* what "kilobyte" and friends meant.
Except Ethernet card manufacturers, modem manufacturers, PCI card manufacturers... oh, hell, just about anyone who transfers something with a clock.
10baseT ethernet transfers data at 10 Mbps. That means 10 x 10^6 bits per second. IDE buses running at 66 MHz list their theoretical maximum as 66 MB/s.
kilo = 1024 is retarded. It only makes sense for things that have to scale in powers of two, like memory. For a long while, "data rate" meant "kilo=1000, mega=1000 kilo" wheras in storage, "kilo=1024". Talk about a recipe for disaster.
Just as an example: here's an article describing Ultra320 SCSI, and PCI bus bandwidth:
Under standard PCI the host bus has a maximum speed of 66 MHz. This allows for a maximum transfer rate of 533 MB/sec across a 64-bit PCI bus.
66 2/3 MHz (M here means what? oh, right, 10^6) times 8 bytes is 533 1/3 MB/s. Where here, "M" means "1000*1000". In MiB/s, it'd be 508.6263 MiB/s.
Is this a problem? Yes. I shouldn't have to pull out a freaking calculator to figure out how long it should take to dump 2 GB of RAM across a 2 GB/s link. It should be one second, not 1.0737418 seconds.
Computer people knew what kilobyte meant.
No we didn't. We've never used kilo consistently. See above - we've talked about CPU speeds in terms of kHz and MHz, meaning 10^3, 10^6, and talked about kilobits/second meaning 10^3 bits per second, talked about kilobytes/second meaning 10^3 bytes/second, and turned around and talked about file sizes where kilobyte means 1024 bytes.
We've never been consistent. The IEC finally owned up to it and admitted it, and asked us to all finally stop being so damned sloppy, and I'm quite glad they did.
Re:definitely a tech-demo thrill
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Pac-Man Turns 25
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and the ghosts had no personalities at all
You never noticed that the ghosts chase you differently?
The original Pacman was all about A*. That's a pathfinding algorithm (google it, there's lots of material on the web), and it can be weighted so that it not only finds the shortest path to a target, but also takes other things into considerations like the easiest terrain etc. So with Pacman, if memory serves me right, one ghost would just wander around randomly, and the other three ghosts used A* algorithms that were configured slightly differently. For instance one ghost would always try to come up behind Pacman, one would try to cut him off from the front, etc.
The ghosts did have personalities. Hence the reason they had names.
Anyone else feel that this post is just as as bad? Welcome to the muck and the mire. You are now exactly what you claim to hate.
No he's not. He's just pointing out irony.
Painting a Jehovah's Witness as wacko (because it's non-mainstream) is ironic, coming from an organization based in Utah, home of the non-mainstream Church of Latter-Day Saints.
It's weak irony, but it is irony. Pot, kettle, black and all that.
The grandparent is not claiming that Mormons are wacko, nor Jehovah's Witnesses. Just claiming that they're both non-mainstream Christian religions, which is true, and one calling the other "wacko" because it's non-mainstream is ironic.
It's weakly ironic because it's a stretch to associate MOG/SCO with Mormons.
But for practical purposes, lowest rpm in the highest gear is usually the best mpg, but not always.
Exactly. It depends on the gearing of the car. If there's enough separation between the top two gears, then you might be better off going faster (especially with an automatic). Of course, this depends a lot on the design of the engine as well. ~300 hp cars are going to behave differently than 100 hp cars for normal highway driving.
My favorite thing to point out to people is that a high performance car can actually get better gas mileage on a hilly road rather than a flat road. That one takes a while to explain.
Hence the reason I hate the stupid rules of thumb that the EPA and everyone else suggests. Learn how your own car works. Measure it. Figure it out. It ain't that hard.
The other person who responded to you on this was correct - they're full of it.
Aerodynamics doesn't come into play until highway speeds. Especially for large vehicles. Plus, the aerodynamics of large vehicles is generally so bad that you can't notice a slight increase.
As an aside, Mythbusters is not a good show to trust for results like this. They've got very sloppy methodology. As a quick example:
1: Trying to prove that a bullet doesn't cause explosive decompression on a plane by overpressurizing a plane at ground level, thinking that only the pressure difference matters. This is true from an energy standpoint, however, the high air density at ground will cushion the resulting explosion dramatically compared to the low air density at flight altitude. Their conclusion is still right, but they could expect much more dramatic results at altitude (especially with their last test).
2: Trying to show that a marching group of people can't hit the resonant frequency of a bridge by building a scale model. You can't do this - the resonant frequency will scale along with the model, so a 1/10 scale model will have a 10X higher resonant frequency. A higher resonant frequency will require more precisely synchronized marchers, and also may be damped anyway by other losses.
I tend to take everything they show with a grain of salt.
It's only for turbulent flow. For laminar flow, it's proportional to velocity, and for yet other kinds, it's proportional to the cube of the velocity. Usually depends on the Reynolds number of the flow.
Figuring out how viscosity depends on velocity is akin to solving the Navier-Stokes equation for the air passing by the car.
Simple example is usually: a tennis ball experiences air resistance proportional to v^2. A volleyball experiences air resistance proportional to v.
Of course, this all assumes that you're in a dense atmosphere, and the atmosphere itself is a Newtonian fluid. Fluid mechanics is nasty. There's a reason they don't cover it in basic physics courses.
The original parent said that wind resistance cubes every time you double your speed.
That's just wrong, no matter what.
If you're talking about power loss through the air, then power loss would increase by a factor of eight every time you double your speed. If you talk about force only, it increases by a factor of four. The original parent was using very poor wording.
Well, you're wrong, my 240SX gets better mileage at 85 MPH than it does at 55 MPH. It's all gearing.
Gearing can be a huge, huge deal if the gap between the overdrive and 3rd gear is large.
Still, I'd doubt that any car gets its best mileage at 85 mph - probably just better than at 55. Aerodynamic losses will be something like 70-80% of total loss at that speed, which means you're starting to hit a very, very steep wall. It's just that very few people actually measure gas mileage at 45 mph - that is, a gear down from your top, in its powerband.
I love looking at the EPA's website on gas mileage, and the little "gas mileage vs. speed" graph they have. Count the peaks in the graph: 1, 2, 3, 4, 5. 5 gear vehicle - so probably a manual transmission. Manual transmission, which means that you're able to keep the car in the powerband much better - hence the smoothed peaks. As if most drivers in the US have a manual. I'd love to see them put up, say, some 3-gear automatic. But, that wouldn't support their conclusions, now would it.
Horsepower is a function of peak torque and RPM.
Yah. It's the product of the two. Horsepower = torque * RPM. First-year physics.:)
Yah, trust me. If I could've gotten a manual transmission, I would've. The ATX in my Mazda is the main failure item on the car. I have to change the transmission fluid religiously to calm my fears of it failing.
I have no idea why automatic transmissions are the norm in the US. I hate automatics. Manuals, just from normal driving, get almost 20% better gas mileage, and can do much better with proper driving. It's insane.
Then again, a lot of people with manuals think they should change to higher gears as early as you can to keep the RPMs low, which kills your gas mileage even worse than having an automatic. The common thought that "engine works harder, uses more gas when RPMs are high" is incredibly wrong.
Yes, this is true. However, typically vehicle's are geared to be most efficient around 55mph. This view is supported by the EPA.
I know. I've heard it from people at the EPA, along with those numbers. They're also wrong. Most modern cars (with overdrive) have a much, much smoother falloff than that at higher speeds. Most highways are 65 now, and most people drive 75 on them. They would notice a 20% or higher drop in fuel economy. And, of course, since you put a peak in the 60s, that means you probably put a dip in the high 50s.
At least, a lot of the foreign-made cars I know have gearings like this. US-made cars, I don't know about. But if you've got an overdrive that kicks in around 45-50, good chance that 55 is not your most fuel efficient speed (at highway speeds).
Well, you sent me Google where people have previously discussed this and it's not so simple; but I'll give that you're probably closer to being right than I am.
*bangs head on keyboard*
OK, my fluid mech professor just shot me. Yah, at laminar flow it's linear, not squared. Squared is *turbulent* flow. Serves me right for trying to remember off the top of my head.
The standard comparison is that a golf ball in flight experiences air resistance proportional to v^2, but a volleyball only experiences resistance proportional to v.
Isn't the whole peak efficiency was the basis behind the hybrid car? Run it right at the top of the power band. If the car's speed doesn't dictate that much revving, pull some of the extra power out and store it in a battery.
Bottom of the power band, not top.
And you can't do that without a continuously variable transmission. The speed of the car is just the RPM of the engine times the gear ratio (or divided, depending on how you define it) times the radius of the tire.
What a hybrid car does is only use the gas engine when the speed of the car is high enough that the gas engine is more efficient than the electric (or when the charge of the battery dips low). Besides, you can't just dump excess power into the battery - obviously, a battery can only store a finite amount of power.
I've often seen underpowered cars perform far worse than expected in terms of fuel economy.
You can also see them perform far better, as well. They're great for simple highway driving, but up and down hills (or with a load) their fuel efficiency will fall apart.
one where I only had the windows open or the fan on.
Drag due to open windows will kill your gas mileage far more than air conditioning does.
Anyway, the air conditioning doesn't do much anyway, just like having the radio on, or the headlights on, won't do squat. The loss due to the alternator existing is far more than the increased loss from increased load. Similar for the air conditioner.
You're on the right track, but you also need to remember that when velocity is doubled, aerodynamic drag is quadrupled. At steady highway speeds, other sources of drag are almost negligible.
You mean other sources of loss, not drag. And that's not true - aerodynamic losses start taking over at highway speeds, but other sources are certainly not negligible.
And anyway, fuel efficiency for an engine can drop very rapidly when you fall out of the power band. Doesn't matter if you reduce your aerodynamic drag by 40% (probably reducing your total overall losses by 20-30%) if your engine efficiency drops by 50% as well.
Which is exactly why the speed limit when from 70 to 55 durring the oil crisis. Someone will correct me, but wind resistance is cubed every time you double your speed. Our old '84 caddilac with trip computer got 25mpg at 64mph, but got 17-19mpg at 70mph. Closer to 28mpg at 55mph.
Every time you double your speed, wind resistance quadruples. It goes with the square of the velocity.
However, that's not the whole story by a long shot, which should be obvious. If the slower you go, the better gas mileage you get, you might think you get infinite gas mileage at a standstill. Of course, you don't.
What makes the difference, then? Gears. See, your engine is extremely efficient in an RPM band - around the torque peak (called the power band). It's most efficient at the bottom of that power band. The gears don't actually help anything - as you learn in basic physics, simple machines don't change the amount of work that needs to be done. What they do is allow the engine to run at a more efficient RPM for a given speed.
So what gears do is put peaks in the fuel efficiency curve. Depending on how a car is geared, 55 mph can be very inefficient, because it could be at the worst spot below the power band, which it is on my 93 Mazda. 55 mph gets me 28 mpg, whereas 65 gets me 30, and 70 gets me 34. 75 gets me about 32, and 80 gets me about 30 again (this is all measured).
It's not just as simple as slowing down. You have to know how your car is geared - if it's got an overdrive, it's very possible that going 55 could hurt your gas mileage via engine inefficiency more than it helps via aerodynamics.
That doesn't mean that 34 is the best gas mileage I get, of course. My peak gas mileage is in the mid-40s, in the peak of the previous gear (if I lock it into 3rd via the shift lock), where it's about 36-37 mpg. At lower speeds, aerodynamics losses are well below rolling resistance, so going slower doesn't help.
Small objects cross their orbits, others orbit them, but the planets comprise the vast majority of material in their orbit. Earth is the only exception, since a considerable portion of the mass in our orbit is also tied up in our moon, which is what is what brings the "double planet" opinion - when taken together, the rest of the material along their orbit can be statistically discounted, since it's only an invisible fraction of the Earth and Moon's combined mass.
The usual claim that the Earth/Moon system is a double planet would be from the orbital dynamics of it, but that's not a good argument - the Moon orbits the Earth, not a point in space (like Charon and Pluto do). Charon is about 8% of Pluto's mass - in other words, they're about an order of magnitude apart. The Earth and the Moon are more like two orders of magnitude apart, and the next closest (Triton and Neptune, I think) are about 4 orders of magnitude apart (actually 3.5). If Triton was just a little bigger - say, Titan sized (factor of 5) - I doubt anyone would call the Earth-Moon a double planet system.
I've never bought the orbital inclination definition. That just defines "primordial planet". If a star captures a rogue planet in a very eccentric orbit, it'll still be a planet. Or if a Jupiter sized object perturbs a smaller planet into an eccentric orbit, it's still a planet.
The "majority of mass in orbit" is a pretty good definition, without even "vast". Ceres would still fail that, and I think even Pluto might just barely sneak in. Depends on how you calculate the "orbit", because Pluto is definitely quite massive - if you said "semimajor axis +/- 5%", Pluto is probably still fine (semimajor axis +/- eccentricity and it'd fail, though). You might pick up Sedna or Quaoar, though, but it's too early to tell.
I've always been fond of simply saying anything that can pull itself into sphere with its own gravity and orbits a star (and nothing else) is a planet. That makes Ceres a planet, though (along with several others).
and it's not unique in its orbit due to other large comets with simmilar orbis and even comparable size, like Sedna
Sedna, incidentally, does not have the same orbit as Pluto. Nowhere near. Sedna is obscenely farther away than Pluto (~500 AU +/- 400 vs. 39 +/- 10). Quaoar is close, but still mostly outside of Pluto's orbit (42 AU).
Oddly enough, Quaoar might win if you define it as "semimajor axis +/- eccentricity" as the region for mass exclusion, because it is very circular. I doubt there's much of anything within that ring, though Pluto is there for a portion of the time. Again, depends on how you calculate it.
de Grey (the theoretical biogerontologist working on aging) has suggested that we shouldn't even bother fixing DNA damage, and I agree with him.
His point is, essentially: we don't need to fix DNA damage. We have an utter *#%!load of cells in our body, and the vast majority of them have perfect genomes. The body's standard way of dealing with really bad mutations is perfect - kill the cell, and let another cell divide to replace it.
The big problem that has is when the "kill the cell" mechanism fails. A lot of the most promising treatments now directly target the failure of those pathways (like p51). My wife's working on one of those, and the biggest problem they have is that the drug works too well, and all the dead cancer cells can poison the body.
de Grey's recommendation is a lot more aggressive - his suggestion is to finish what nature started, and get rid of cancer's exploitation of the one vulnerability in the body's DNA repair mechanism - by eliminating the possibility of infinite copying to begin with by eliminating telomerase completely, and lengthening telomeres ex vivo in a controlled environment. It's quite smart, if a little insane - cancers will still form, but die on their own before they even get macroscopic.
Of course. But there's hardly any practical difference between atheism and pantheism.
Uh, I know a lot of people that would disagree with you (including myself). Pantheism has more resemblance with monotheism than atheism, except for the fact that pantheism is more justifiable than most monotheistic dogmas. For the most part, the difference between pantheism and monotheism is one of definition.
Your second point, of course, is a matter of religious belief. Certainly many older religions believed that the Gods didn't give a rat's ass about humans.
No, the problem is it brings us right back to the dilemma- something cannot be the cause of it's own existence.
As I've said, that statement is simply wrong. Even implying causality means that you're introducing a higher-level dimension that you've embedded it in. Without causality, there's no reason that something cannot be the cause of itself.
More importantly, you're actually implying a lot about that extra dimension that you've introduced. It has to be a lot like time, in fact, because you're implying that spatial relations in that dimension are absolute and have meaning.
So saying "the Universe cannot be the cause of itself" is simply wrong - the only way that's true is if the Universe is embedded in a fifth dimension (timelike, orthogonal to our time) and in which case, just redefine the Universe one level up (including the new time dimension). Then the Universe can, in fact, be the cause of itself.
Or just start off by defining spacetime as a point in an N-dimensional space (where N is all possible dimensions), and the Universe as the set of all connected spacetime. Poof, the Universe can be the cause of itself, because there are no higher-order dimensions to embed it in.
When I (and you) use words like 'before' concerning what happened casually prior to the big bang, that's more of an expression of the limits of human language to describe events not in space-time. It's difficult to describe an entity or whatever else that is 'outside' of our space-time universe as being responsible for it's coming into being without invoking tensed human language.
It's not a limitation of the language. It's a limitation of the construct that you're forming. When you say "before", "after", "in front of", "behind" - you're implicitly creating a dimension. Without that dimension, trying to use causality to disprove something ("X can't cause X, because it would have had to exist before X") is patently wrong.
The phrase "before the Big Bang" is really simply poor wording by most people, as the Big Bang isn't really a time - more a limit. It's a lot like a black hole - while the proper time it takes something to fall into a black hole is finite, the observed time from outside is infinite. Time itself "began" then - but that's like saying the real number line "begins" at minus infinity.
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At open throttle, you *can* shift lower than you otherwise could. If, however, you're not accellerating that hard, it's another story.
Accelerating hard or under load (going up a hill, or carrying weight). Which of course leads to the wonderful fact that the best gas mileage for many trucks is obtained when going through hilly country. Since you don't use that much extra fuel to move up the hill (since you throttle less), the energy you store can improve your gas mileage when you come down. For large-engined vehicles, this can be a *huge* deal (difference between 20 and 30 mpg, in some cases).
For small cars, though, hills can hurt gas mileage. It's things like this that make me really ticked off at the EPA regarding gas mileage. Don't spread complete crap to people, just tell them the truth.
They just silently changed it, causing shitloads of confusion along the way. Of all the alternatives in this mess, they choose the one which could ruin an engineers day, only for the purpose of having your drive look a few % larger.
Silently? On all the hard drives I had for a long time, they specifically state what a MB (or GB) was - one billion bytes.
Honestly, it's fairly retarded to have to define what a standard is when you're using it.
You do realize, though, that you're complaining that they violated a convention to follow a standard, right? Standards are far more useful than conventions, because a standard is rigidly defined.
This isn't just hard drive manufacturers, either. Theoretical data rate is often expressed in MB/s, because it's just transfer frequency times payload size. Hell, you can figure out rough hard drive capacity by bit density times area.
The only place where binary prefixes are useful is for memory. The only place.
I mean, jeez. The computing industry doesn't even agree on the right case on the prefix (kilo is a lowercase k, not uppercase). We haven't been consistent. This wasn't because of marketing people, it was because we were sloppy. Whoever pointed it out to us, it's our own fault. Own up, and fix it. kB = 1000 bytes. KiB (note the uppercase!) is 1024 bytes. At least now there's a standard. It's one freaking letter.
Your hard drive uses something other than binary to address the data stored on it?
Yah, LBA (logical block addressing). You ask the drive "give me block X", and it gives you block X. No binary involved. The fact that the numbers are transmitted over binary is unimportant. It could've been done over ternary, or avian squawkspeak consisting of fifteen symbols.
"Binary addressing" means "addressed by a bunch of address lines which hold values in binary". So a 1024-byte SRAM has 10 address lines. If I want to add more capacity, I have to add another address line, which gives me 2048 bytes. In other words, memory sizes are 2^N, where N is the number of address lines. Here, it does matter that the address is transmitted via binary: if each address line held 3 states, the total memory size would be 3^N, not 2^N.
Note that most modern memory multiplex the address lines (as having 30 address lines for a gigabyte of memory is awkward) into row and column addresses, but it's still binary addressing, and memory sizes still need to scale by powers of 2.
Yes. And trust me, this isn't the only one.
66 (2/3) MHz times 8-bytes wide is 533 (1/3) MB/s. Here mega means 10^6, not 2^20. If it were megabinary, it'd be 508-something MiB/s. (*)
Look, computer usage of kilo has always sucked and been inconsistent. Always. Own up to it and fix it.
(*: I find it amusing that in order to find an example, I had to find one where they used "66 MHz" incorrectly, but no one actually writes 66.66... MHz, so forgive the irony.)
"1024 except for metrics being stated in bits or hertz"
So a 2 GHz link that's 1 byte wide transfers data at 1.862 GB/s? This is just silly.
Except Ethernet card manufacturers, modem manufacturers, PCI card manufacturers... oh, hell, just about anyone who transfers something with a clock.
10baseT ethernet transfers data at 10 Mbps. That means 10 x 10^6 bits per second. IDE buses running at 66 MHz list their theoretical maximum as 66 MB/s.
kilo = 1024 is retarded. It only makes sense for things that have to scale in powers of two, like memory. For a long while, "data rate" meant "kilo=1000, mega=1000 kilo" wheras in storage, "kilo=1024". Talk about a recipe for disaster.
Just as an example: here's an article describing Ultra320 SCSI, and PCI bus bandwidth:
66 2/3 MHz (M here means what? oh, right, 10^6) times 8 bytes is 533 1/3 MB/s. Where here, "M" means "1000*1000". In MiB/s, it'd be 508.6263 MiB/s.
Is this a problem? Yes. I shouldn't have to pull out a freaking calculator to figure out how long it should take to dump 2 GB of RAM across a 2 GB/s link. It should be one second, not 1.0737418 seconds.
Computer people knew what kilobyte meant.
No we didn't. We've never used kilo consistently. See above - we've talked about CPU speeds in terms of kHz and MHz, meaning 10^3, 10^6, and talked about kilobits/second meaning 10^3 bits per second, talked about kilobytes/second meaning 10^3 bytes/second, and turned around and talked about file sizes where kilobyte means 1024 bytes.
We've never been consistent. The IEC finally owned up to it and admitted it, and asked us to all finally stop being so damned sloppy, and I'm quite glad they did.
You never noticed that the ghosts chase you differently?
The ghosts did have personalities. Hence the reason they had names.
Anyone else feel that this post is just as as bad? Welcome to the muck and the mire. You are now exactly what you claim to hate.
No he's not. He's just pointing out irony.
Painting a Jehovah's Witness as wacko (because it's non-mainstream) is ironic, coming from an organization based in Utah, home of the non-mainstream Church of Latter-Day Saints.
It's weak irony, but it is irony. Pot, kettle, black and all that.
The grandparent is not claiming that Mormons are wacko, nor Jehovah's Witnesses. Just claiming that they're both non-mainstream Christian religions, which is true, and one calling the other "wacko" because it's non-mainstream is ironic.
It's weakly ironic because it's a stretch to associate MOG/SCO with Mormons.
But for practical purposes, lowest rpm in the highest gear is usually the best mpg, but not always.
Exactly. It depends on the gearing of the car. If there's enough separation between the top two gears, then you might be better off going faster (especially with an automatic). Of course, this depends a lot on the design of the engine as well. ~300 hp cars are going to behave differently than 100 hp cars for normal highway driving.
My favorite thing to point out to people is that a high performance car can actually get better gas mileage on a hilly road rather than a flat road. That one takes a while to explain.
Hence the reason I hate the stupid rules of thumb that the EPA and everyone else suggests. Learn how your own car works. Measure it. Figure it out. It ain't that hard.
The other person who responded to you on this was correct - they're full of it.
Aerodynamics doesn't come into play until highway speeds. Especially for large vehicles. Plus, the aerodynamics of large vehicles is generally so bad that you can't notice a slight increase.
As an aside, Mythbusters is not a good show to trust for results like this. They've got very sloppy methodology. As a quick example:
1: Trying to prove that a bullet doesn't cause explosive decompression on a plane by overpressurizing a plane at ground level, thinking that only the pressure difference matters. This is true from an energy standpoint, however, the high air density at ground will cushion the resulting explosion dramatically compared to the low air density at flight altitude. Their conclusion is still right, but they could expect much more dramatic results at altitude (especially with their last test).
2: Trying to show that a marching group of people can't hit the resonant frequency of a bridge by building a scale model. You can't do this - the resonant frequency will scale along with the model, so a 1/10 scale model will have a 10X higher resonant frequency. A higher resonant frequency will require more precisely synchronized marchers, and also may be damped anyway by other losses.
I tend to take everything they show with a grain of salt.
Is that only for certain designs
It's only for turbulent flow. For laminar flow, it's proportional to velocity, and for yet other kinds, it's proportional to the cube of the velocity. Usually depends on the Reynolds number of the flow.
Figuring out how viscosity depends on velocity is akin to solving the Navier-Stokes equation for the air passing by the car.
Simple example is usually: a tennis ball experiences air resistance proportional to v^2. A volleyball experiences air resistance proportional to v.
Of course, this all assumes that you're in a dense atmosphere, and the atmosphere itself is a Newtonian fluid. Fluid mechanics is nasty. There's a reason they don't cover it in basic physics courses.
Of course you do! It just takes infinitly long ;-)
No, you don't. The car consumes gas standing still.
The original parent said that wind resistance cubes every time you double your speed.
That's just wrong, no matter what.
If you're talking about power loss through the air, then power loss would increase by a factor of eight every time you double your speed. If you talk about force only, it increases by a factor of four. The original parent was using very poor wording.
Well, you're wrong, my 240SX gets better mileage at 85 MPH than it does at 55 MPH. It's all gearing.
:)
Gearing can be a huge, huge deal if the gap between the overdrive and 3rd gear is large.
Still, I'd doubt that any car gets its best mileage at 85 mph - probably just better than at 55. Aerodynamic losses will be something like 70-80% of total loss at that speed, which means you're starting to hit a very, very steep wall. It's just that very few people actually measure gas mileage at 45 mph - that is, a gear down from your top, in its powerband.
I love looking at the EPA's website on gas mileage, and the little "gas mileage vs. speed" graph they have. Count the peaks in the graph: 1, 2, 3, 4, 5. 5 gear vehicle - so probably a manual transmission. Manual transmission, which means that you're able to keep the car in the powerband much better - hence the smoothed peaks. As if most drivers in the US have a manual. I'd love to see them put up, say, some 3-gear automatic. But, that wouldn't support their conclusions, now would it.
Horsepower is a function of peak torque and RPM.
Yah. It's the product of the two. Horsepower = torque * RPM. First-year physics.
But then it hit me - automatic transmission.
Yah, trust me. If I could've gotten a manual transmission, I would've. The ATX in my Mazda is the main failure item on the car. I have to change the transmission fluid religiously to calm my fears of it failing.
I have no idea why automatic transmissions are the norm in the US. I hate automatics. Manuals, just from normal driving, get almost 20% better gas mileage, and can do much better with proper driving. It's insane.
Then again, a lot of people with manuals think they should change to higher gears as early as you can to keep the RPMs low, which kills your gas mileage even worse than having an automatic. The common thought that "engine works harder, uses more gas when RPMs are high" is incredibly wrong.
Yes, this is true. However, typically vehicle's are geared to be most efficient around 55mph. This view is supported by the EPA.
I know. I've heard it from people at the EPA, along with those numbers. They're also wrong. Most modern cars (with overdrive) have a much, much smoother falloff than that at higher speeds. Most highways are 65 now, and most people drive 75 on them. They would notice a 20% or higher drop in fuel economy. And, of course, since you put a peak in the 60s, that means you probably put a dip in the high 50s.
At least, a lot of the foreign-made cars I know have gearings like this. US-made cars, I don't know about. But if you've got an overdrive that kicks in around 45-50, good chance that 55 is not your most fuel efficient speed (at highway speeds).
Well, you sent me Google where people have previously discussed this and it's not so simple; but I'll give that you're probably closer to being right than I am.
*bangs head on keyboard*
OK, my fluid mech professor just shot me. Yah, at laminar flow it's linear, not squared. Squared is *turbulent* flow. Serves me right for trying to remember off the top of my head.
The standard comparison is that a golf ball in flight experiences air resistance proportional to v^2, but a volleyball only experiences resistance proportional to v.
Isn't the whole peak efficiency was the basis behind the hybrid car? Run it right at the top of the power band. If the car's speed doesn't dictate that much revving, pull some of the extra power out and store it in a battery.
Bottom of the power band, not top.
And you can't do that without a continuously variable transmission. The speed of the car is just the RPM of the engine times the gear ratio (or divided, depending on how you define it) times the radius of the tire.
What a hybrid car does is only use the gas engine when the speed of the car is high enough that the gas engine is more efficient than the electric (or when the charge of the battery dips low). Besides, you can't just dump excess power into the battery - obviously, a battery can only store a finite amount of power.
I've often seen underpowered cars perform far worse than expected in terms of fuel economy.
You can also see them perform far better, as well. They're great for simple highway driving, but up and down hills (or with a load) their fuel efficiency will fall apart.
one where I only had the windows open or the fan on.
Drag due to open windows will kill your gas mileage far more than air conditioning does.
Anyway, the air conditioning doesn't do much anyway, just like having the radio on, or the headlights on, won't do squat. The loss due to the alternator existing is far more than the increased loss from increased load. Similar for the air conditioner.
You're on the right track, but you also need to remember that when velocity is doubled, aerodynamic drag is quadrupled. At steady highway speeds, other sources of drag are almost negligible.
You mean other sources of loss, not drag. And that's not true - aerodynamic losses start taking over at highway speeds, but other sources are certainly not negligible.
And anyway, fuel efficiency for an engine can drop very rapidly when you fall out of the power band. Doesn't matter if you reduce your aerodynamic drag by 40% (probably reducing your total overall losses by 20-30%) if your engine efficiency drops by 50% as well.
Air resistance is proportional to the cube of the velocity.
Square of the velocity, with laminar flow. In other flow situations, it's linear with velocity (or cubic in yet others).
And many cars could still do a lot to improve their aerodynamics. For God's sake, they still make the Hummer.
Which is exactly why the speed limit when from 70 to 55 durring the oil crisis. Someone will correct me, but wind resistance is cubed every time you double your speed. Our old '84 caddilac with trip computer got 25mpg at 64mph, but got 17-19mpg at 70mph. Closer to 28mpg at 55mph.
Every time you double your speed, wind resistance quadruples. It goes with the square of the velocity.
However, that's not the whole story by a long shot, which should be obvious. If the slower you go, the better gas mileage you get, you might think you get infinite gas mileage at a standstill. Of course, you don't.
What makes the difference, then? Gears. See, your engine is extremely efficient in an RPM band - around the torque peak (called the power band). It's most efficient at the bottom of that power band. The gears don't actually help anything - as you learn in basic physics, simple machines don't change the amount of work that needs to be done. What they do is allow the engine to run at a more efficient RPM for a given speed.
So what gears do is put peaks in the fuel efficiency curve. Depending on how a car is geared, 55 mph can be very inefficient, because it could be at the worst spot below the power band, which it is on my 93 Mazda. 55 mph gets me 28 mpg, whereas 65 gets me 30, and 70 gets me 34. 75 gets me about 32, and 80 gets me about 30 again (this is all measured).
It's not just as simple as slowing down. You have to know how your car is geared - if it's got an overdrive, it's very possible that going 55 could hurt your gas mileage via engine inefficiency more than it helps via aerodynamics.
That doesn't mean that 34 is the best gas mileage I get, of course. My peak gas mileage is in the mid-40s, in the peak of the previous gear (if I lock it into 3rd via the shift lock), where it's about 36-37 mpg. At lower speeds, aerodynamics losses are well below rolling resistance, so going slower doesn't help.
Small objects cross their orbits, others orbit them, but the planets comprise the vast majority of material in their orbit. Earth is the only exception, since a considerable portion of the mass in our orbit is also tied up in our moon, which is what is what brings the "double planet" opinion - when taken together, the rest of the material along their orbit can be statistically discounted, since it's only an invisible fraction of the Earth and Moon's combined mass.
The usual claim that the Earth/Moon system is a double planet would be from the orbital dynamics of it, but that's not a good argument - the Moon orbits the Earth, not a point in space (like Charon and Pluto do). Charon is about 8% of Pluto's mass - in other words, they're about an order of magnitude apart. The Earth and the Moon are more like two orders of magnitude apart, and the next closest (Triton and Neptune, I think) are about 4 orders of magnitude apart (actually 3.5). If Triton was just a little bigger - say, Titan sized (factor of 5) - I doubt anyone would call the Earth-Moon a double planet system.
I've never bought the orbital inclination definition. That just defines "primordial planet". If a star captures a rogue planet in a very eccentric orbit, it'll still be a planet. Or if a Jupiter sized object perturbs a smaller planet into an eccentric orbit, it's still a planet.
The "majority of mass in orbit" is a pretty good definition, without even "vast". Ceres would still fail that, and I think even Pluto might just barely sneak in. Depends on how you calculate the "orbit", because Pluto is definitely quite massive - if you said "semimajor axis +/- 5%", Pluto is probably still fine (semimajor axis +/- eccentricity and it'd fail, though). You might pick up Sedna or Quaoar, though, but it's too early to tell.
I've always been fond of simply saying anything that can pull itself into sphere with its own gravity and orbits a star (and nothing else) is a planet. That makes Ceres a planet, though (along with several others).
and it's not unique in its orbit due to other large comets with simmilar orbis and even comparable size, like Sedna
Sedna, incidentally, does not have the same orbit as Pluto. Nowhere near. Sedna is obscenely farther away than Pluto (~500 AU +/- 400 vs. 39 +/- 10). Quaoar is close, but still mostly outside of Pluto's orbit (42 AU).
Oddly enough, Quaoar might win if you define it as "semimajor axis +/- eccentricity" as the region for mass exclusion, because it is very circular. I doubt there's much of anything within that ring, though Pluto is there for a portion of the time. Again, depends on how you calculate it.
de Grey (the theoretical biogerontologist working on aging) has suggested that we shouldn't even bother fixing DNA damage, and I agree with him.
His point is, essentially: we don't need to fix DNA damage. We have an utter *#%!load of cells in our body, and the vast majority of them have perfect genomes. The body's standard way of dealing with really bad mutations is perfect - kill the cell, and let another cell divide to replace it.
The big problem that has is when the "kill the cell" mechanism fails. A lot of the most promising treatments now directly target the failure of those pathways (like p51). My wife's working on one of those, and the biggest problem they have is that the drug works too well, and all the dead cancer cells can poison the body.
de Grey's recommendation is a lot more aggressive - his suggestion is to finish what nature started, and get rid of cancer's exploitation of the one vulnerability in the body's DNA repair mechanism - by eliminating the possibility of infinite copying to begin with by eliminating telomerase completely, and lengthening telomeres ex vivo in a controlled environment. It's quite smart, if a little insane - cancers will still form, but die on their own before they even get macroscopic.
Of course. But there's hardly any practical difference between atheism and pantheism.
Uh, I know a lot of people that would disagree with you (including myself). Pantheism has more resemblance with monotheism than atheism, except for the fact that pantheism is more justifiable than most monotheistic dogmas. For the most part, the difference between pantheism and monotheism is one of definition.
Your second point, of course, is a matter of religious belief. Certainly many older religions believed that the Gods didn't give a rat's ass about humans.
No, the problem is it brings us right back to the dilemma- something cannot be the cause of it's own existence.
As I've said, that statement is simply wrong. Even implying causality means that you're introducing a higher-level dimension that you've embedded it in. Without causality, there's no reason that something cannot be the cause of itself.
More importantly, you're actually implying a lot about that extra dimension that you've introduced. It has to be a lot like time, in fact, because you're implying that spatial relations in that dimension are absolute and have meaning.
So saying "the Universe cannot be the cause of itself" is simply wrong - the only way that's true is if the Universe is embedded in a fifth dimension (timelike, orthogonal to our time) and in which case, just redefine the Universe one level up (including the new time dimension). Then the Universe can, in fact, be the cause of itself.
Or just start off by defining spacetime as a point in an N-dimensional space (where N is all possible dimensions), and the Universe as the set of all connected spacetime. Poof, the Universe can be the cause of itself, because there are no higher-order dimensions to embed it in.
When I (and you) use words like 'before' concerning what happened casually prior to the big bang, that's more of an expression of the limits of human language to describe events not in space-time. It's difficult to describe an entity or whatever else that is 'outside' of our space-time universe as being responsible for it's coming into being without invoking tensed human language.
It's not a limitation of the language. It's a limitation of the construct that you're forming. When you say "before", "after", "in front of", "behind" - you're implicitly creating a dimension. Without that dimension, trying to use causality to disprove something ("X can't cause X, because it would have had to exist before X") is patently wrong.
The phrase "before the Big Bang" is really simply poor wording by most people, as the Big Bang isn't really a time - more a limit. It's a lot like a black hole - while the proper time it takes something to fall into a black hole is finite, the observed time from outside is infinite. Time itself "began" then - but that's like saying the real number line "begins" at minus infinity.