Science desk | ||
---|---|---|
< December 20 | << Nov | December | Jan >> | December 22 > |
Welcome to the Wikipedia Science Reference Desk Archives |
---|
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages. |
Is gasoline vapor heavier than air. I am concerned about storage of small containers of gas in heated garage. —Preceding unsigned comment added by 72.240.19.105 ( talk) 02:50, 21 December 2007 (UTC)
I've not had my eclectus that long. He likes his seed, he likes nuts, he likes table scraps but he doesn't seem that bothered about fruit. What percentage of his diet is supposed to be made up of fruit and veg? —Preceding unsigned comment added by 84.64.109.187 ( talk) 08:27, 21 December 2007 (UTC)
I have an assingnment on manufacturing that goes like this:
You are requested to draw up a basic work scheme for the production of a functional
shaft, plain bearing and wheel assembly which is going to be used for a skateboard
undercarriage.
Plain bearing Shaft Wheel The plain bearing is fixed to the wheel and it rotates freely on the shaft. In your report identify; The materials which can be used for the three individual parts The manufacturing techniques and procedures to manufacture the parts Any post manufacture surface treatments to reduce wear and increase lifetime It is suggested to back your choices with relevant information
Can anyone direct me to appropiate sites where a good general idea can be given? P.S. I would like to construct the elements out of organic materials if possible. —Preceding unsigned comment added by 193.188.46.254 ( talk) 09:17, 21 December 2007 (UTC)
Why re-invent the wheel? Heh. No, seriously. The specifications and designs for skateboard wheels (and just about everything else that is manufactured) are covered already by
standards. The trick is to find the standard that will cover what you're looking for. Here's how to do this. There are numerous organizations out there that publish standards, depending on what their focus is. So, for instance the organization
ASTM is one, as is the
ANSI,
DIN,
IEEE,
BSI and other organizations. It would be quite difficult (unless you already knew) which of these organizations would be the one that would publish a standard that you're looking for. Fortunately, there's a private company called
ILI Standards that keeps an updated database that indexes all of the Standards in the world - or pretty close to all of them. I don't know what "ILI" stands for - nobody knows (or at least nobody that I know knows).
Now here's where it gets tricky. This company makes its money by selling standards that they print. Because of this they do not make the standards freely available online or anywhere else - they're very fussy about that. You either have to purchase one of their standards (which can actually be expensive), or try to find the standard you're looking for in some library. It is often difficult to know whether a particular library has the standard you're looking for; quite often libraries do not list the standards they have in their collection in their online catalogs. Instead, you need to contact the library's Reference Desk directly and ask if they have "such and such standard" in their collection. If they have what you're looking for, you can go make some photocopies of the pages that cover what you're interested in doing. The standards will describe what type of materials need to be used, they'll often provide diagrams and blueprints for the design, and they'll give specifications for tensions stresses, etc.
Only some libraries collect standards, of course. The best libraries to look for standards are ones that support some kind of research involving manufacturing, engineering, design, etc. So libraries that are associated with universities that offer degrees in these subjects would be good places to look for standards. I do not know of any library that has all of the standards in the world - standards cost a lot of money, and unless the library staff that orders the standards feels that there would be a need for a particular standard, it is unlikely that they would spend their often limited resources on purchasing standards to put in their collection if they believed that they would never be used by anyone. What you're looking for is a standard for skateboards, and quite frankly this is not one of those things (I'm guessing here) that would be included in a lot of libraries. It might be tricky to find a library that has the standard you're looking for. To make things worse, libraries do not ship standards from one library to the next through their Inter-Library Loan system. This is due to copyright restrictions on them. So if you're lucky you might find a library close to you that has the standard you're looking for. Then you can go and make photocopies for free. Otherwise, in order to get the standard, you're going to have to pay for it.
ILI Standards has an online database where you may search for what you're looking for; it's called ILI Infobase. I did a cursory search using the word "skateboard" and came up with this standard:
Standard Number: BS 5715(1993)
English Title: SPECIFICATION FOR SKATEBOARDS FOR RECREATIONAL AND SPORTS USE
Version Date: 03/15/1993
Country: United Kingdom (GB)
Summary: Specifies requirements for non-motorized skateboards which are supplied as complete articles for use by a single rider at a time. Coverage includes definitions, performance, marking, and design and construction. Also includes annexes and diagrams.
Committee: TCM/56
Publisher: BSI (BRITISH STANDARDS INSTITUTION)
389 CHISWICK HIGH ROAD
LONDON
W4 4AL
Table of Contents:
Committees responsible
Foreword
Specification
1 Scope
2 Normative references
3 Definitions
4 Design and construction
5 Performance
6 Advice to users
7 Marking
Annexes
A Skateboard safety code
B Advice on maintenance and use
C Schedule of tests
D Wheel friction test
E Speed test
F Endurance test
G External design
H Drop test
J Impact test
K Pulsating force test for deflection of metal decks
Figures
1 Major components of a skateboard
2 Radiusing of edges of deck
D.1 Diagram of friction test apparatus
F.1 Diagram of endurance test apparatus
G.1 Example of use of test cylinder
H.1 Diagram of apparatus for drop test
K.1 Diagram of arrangement for pulsating force test
List of references
Although this standard has been superceded by another (BS EN 13613), the newer standard seems to focus not on the "nuts and bolts" of the construction of the wheel assemblies of skateboards, but is more focused on safety issues. So I would use the standard I've quoted to find diagrams and descriptions of wheel assemblies. I hopt this helps. -- Saukkomies 08:30, 21 December 2007 (UTC)
The latest propaganda campaign by the Australian Government is that all sun-tanning is extremely dangerous and that you absolutely should not tan.
The campaign also tries to explain that we get enough Vitamin D from foods, that even though you feel and look healthier with a tan the risks are not worth it.
You can view the TV ad here:
http://www.darksideoftanning.com.au/campaign/tvc.aspx (the government has launched a whole website and media campaign against tanning
Is this paranoia or is well-founded truth? Previously I had asked on the reference desk about tanning, and discovered it's the UV rays that actually convert the Vitamin D and give you a tan. I also know it kills bacteria on the skin, and the sun helps you sweat, increases blood flow and has other benefits. Should I avoid the sun completely or is this campaign absolute nonsense to scare the masses into subjection?
Rfwoolf (
talk)
11:48, 21 December 2007 (UTC)
Well, what the ad campaign fails to clarify, is what if you're not part of the pale-white caucasion section of the population? What if you have a natural olive-brown skin and can in fact tolerate a bit of suntan? Well then their ad campaign would still have you believe that tanning is still 100% out of the question. As to why this is "propaganda", it's obvious that it does its best to illicit fear and other emotional responses in order to get people to take action. In a hypothetical case tanning would become taboo, and any individual that dares to go to the beach and lie in the sun would have dozens of people pointing at them and saying "haven't you hear? You're about to get cancer". The ad fails to offer any balance - the balance is that certain skin tones are more susceptable to skin cancer than others, and that if you have a darker skin tone you can tan for longer periods or spend more time outdoors. That's the clarification I'm after. Because I have a darker skin tone I'm definitely going to be spending some time tanning, no thanks to this blatant shock-campaign. Rfwoolf ( talk) 08:08, 22 December 2007 (UTC)
I've been wondering for a while why (to my knowledge) carnivores are not eaten anywhere on the world. I know some cultures eat dogs, but these are not obligate carnivores...brown bears are eaten, but they are omniovorous, and I have never heard of polar bears being eaten. We do eat carnivorous fish, reptiles and birds, so it seems to be restricted to carnivorous mammals. Is it just because they would not taste good, or would it be unhealthy to eat carnivores? And if the latter, why? -- Ferkelparade π 12:20, 21 December 2007 (UTC)
We do eat lots of different carnivores. Most of the fish we eat are carnivorous, for instance. However, there's a problem with eating mammalian carnivore species - it has to do with the buildup of toxins (and even good things) in the internal organs and tissues of carnivores. Toxins are concentrated in the bodies of animals (and humans) the further one goes up the food chain. One of the most pernicious substances, though, is actually
Vitamin A, which builds up in carnivores' livers and other organs - but especially livers. People
will die or get very very sick if they eat too much Vitamin A. An example is the story of
Xavier Mertz, an Antarctic explorer, who died after eating the liver of his sled dogs. So maybe as a result of this human societies developed
food taboos regarding the eating of carnivores. --
Saukkomies
08:45, 21 December 2007 (UTC)
The obvious answer is, it wouldn't be practical. What we are trying to do is get energy. Where does this energy come from? The sun. But we can't absorb that energy directly, so we have to use intermediaries to get that energy. We can eat plants, or animals that eat plants. But why would we want to eat animals that eat animals that eat plants? Cut out the middle man, it's inefficient. It would be pointless to raise carnivores to eat them, because them we have to also raise herbivoirs to feed the carnivores. But we can just eat the herbivores directly ourselves. It's more cost and energy efficient that way. Also like someone else said, we do eat some carnivores, in the form of fish, but no one is raising those fish. We just pluck them from the trees so to speak. We don't have to provide their food source, like we would with farm animals. Also we can't consume their food source either, well at least no one would want to on a regular basis. 64.236.121.129 ( talk) 17:36, 21 December 2007 (UTC)
Cats are obligate carnivores, and according to cat meat, are eaten in certain parts of the world. So the basic premise that carnivorous mammal meat is never eaten is untrue. I think the other responses give good reasons why it is not widely eaten (e.g., inefficient use of resources in farmed animals; concentration of toxins and prevalence of parasites in wild animals). -- Coneslayer ( talk) 17:58, 21 December 2007 (UTC)
MyD88-/- mice were generated as described and backcrossed for 9 generations on an H-2d (BALB/c) background. - what's the backcrossing necessary for? -- Seans Potato Business 20:15, 12 December 2007 (UTC)
That's weird...we answered this question on Dec 12th. What's it doing back here again? The OP's signature is even from Dec 12th. SteveBaker ( talk) 21:04, 21 December 2007 (UTC)
It seems that professors will often tell stories or use examples that just are not true. The story I have the biggest problem with is about slack action in trains. It goes something like this --It is impossible for a locomotive to start a 50 car train if all the slack is taken out. (ie the train in stretched) Therefore the engineer must back up his locomotive and bunch up the slack. Then he can move the train because he only has to pull one car at a time like 1,2,3,4,5 and so on." This is simply not true. How does the engineer start the train. He gets 6 locomotives with 6000 HP each for a total of 36000 Horsepower and he hooks it up to a 100 car train and with no slack in it just gives it hell and it will pull that coal train like there is no tomorrow. Locomotives have so much power that if an engineer were to follow the teachings of the professor he or she would lose their job because they would rip train apart from the jolt of the slack action.
Why then is this still taught? —Preceding unsigned comment added by 66.228.239.18 ( talk) 18:50, 21 December 2007 (UTC)
6 locomotives is indeed a bit much, the BNSF coal trains that pass through my town routinly have 3-4 units and they are always the newest- SD70ACe, or somtimes GEVOs from General electric. Either way both types are in the 4000 HP range and they handle the 15000 ton trains with ease. Secondly on the artical about diesel locomtives it states "the electric drive system is designed to produce maximum traction motor torque at start-up, which explains why modern locomotives are capable of starting trains weighing in excess of 15,000 tons, even on ascending grades. Current technology allows a locomotive to develop as much as 30 percent of its loaded driver weight in tractive force, amounting to some 120,000 pounds for a large, six-axle freight (goods) unit. In fact, a consist of such units can produce more than enough drawbar pull at start-up to damage or derail cars (if on a curve), or break couplers (the latter being referred to in North American railroad slang as "jerking a lung"). Therefore, it is incumbent upon the engineer (driver) to carefully monitor the amount of power being applied at start-up to avoid damage. In particular, "jerking a lung" could be a calamitous matter if it were to occur on an ascending grade." This being said it appears taht the professor's assertion is incorrect as there is acctualy more than enough power avalible. —Preceding unsigned comment added by 66.228.239.18 ( talk) 20:32, 21 December 2007 (UTC)
Good points all of them. However as part of the thought experiment goes the fuel consumption is no object to the professor. The professor states that it is physicaly impossible to move a 15000 ton train that has been streched out. I would have no problem with taking the professor to the local railroad yard and watching them start the trains. I've never heard slack action on a priortiy coal train... —Preceding unsigned comment added by 66.228.239.18 ( talk) 21:01, 21 December 2007 (UTC)
If I'm in a fast-food line, is it okay to shift my automatic car into neutral for like a minute or so? I'm trying to save gas, but I don't want to mess up my engine. 71.218.36.45 ( talk) 20:03, 21 December 2007 (UTC)
But, I've heard turning the engine on and off also wastes gas. 71.218.36.45 ( talk) 20:15, 21 December 2007 (UTC)
Ok, I don't have a Mini or a Prius. I have a 2004 Hyundai Elantra. It is fuel injected, but I've heard it still wastes gas if you turn off the engine and quickly start it up again. Back to my original question, should I put my car in Neutral if I'm going to be waiting in line, or is Park better? 71.218.36.45 ( talk) 21:04, 21 December 2007 (UTC)
Which one is better? (please, reply only if you really have something meaningful to say) -- Taraborn ( talk) 20:10, 21 December 2007 (UTC)
Something meaningful to say : You need both for a proper Baseball game. I'd say some combination of the two is appropriate for most situations. APL ( talk) 01:11, 22 December 2007 (UTC)
This concept of which is better - cooperation or competition - is the basis of the Nash Equilibrium theory that was named after John Forbes Nash, who won the 1994 Nobel Prize in Economics for it. Nash is also the real-life person that the movie A Beautiful Mind was based on. -- Saukkomies 02:30, 22 December 2007 (UTC)
Out of curiosity, how much would annual greenhouse gas emissions be cut down if everyone got fuel efficient cars? Someguy1221 ( talk) 21:12, 21 December 2007 (UTC)
Globally, transportation fuels are about 14% of total greenhouse gas emissions. My recollection is that cars represent about half of that, with the rest goes to planes, trains, buses, and heavy trucks, etc. So lets call it 7% of the global total. You need to estimate current average fuel economy and compare that to some guess for how things will improve. The corporate average fuel economy standards in the US, which are among the most lax in the world, require the current fleet of cars to average at least 27 miles per gallon (or 21 for SUVs and light trucks). In practice, existing cars are nearly always worse than that because efficiency tends to decline with age. For the sake of argument, lets pessimistically say that all the cars still in operation really only average 15 miles per gallon. If you replace them all with Priuses which have a real world performance of ~45+ miles per gallon, then you'd shave off as much as 2/3 of that 7% of the total gas emissions. In other words, replacing all the cars might (optimistically) net you as much as a 4.5% reduction in total greenhouse gas emissions. Assuming your don't increase the total number of cars in operation, or the amount that people are driving, etc. Dragons flight ( talk) 23:29, 21 December 2007 (UTC)
Why is the meat inside a cornish pasty and certain sausage rolls grey? -- Seans Potato Business 21:28, 21 December 2007 (UTC)
What is the source of the energy in this device? I dont think its the gravity... 79.176.187.141 ( talk) 23:48, 21 December 2007 (UTC)
Science desk | ||
---|---|---|
< December 20 | << Nov | December | Jan >> | December 22 > |
Welcome to the Wikipedia Science Reference Desk Archives |
---|
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages. |
Is gasoline vapor heavier than air. I am concerned about storage of small containers of gas in heated garage. —Preceding unsigned comment added by 72.240.19.105 ( talk) 02:50, 21 December 2007 (UTC)
I've not had my eclectus that long. He likes his seed, he likes nuts, he likes table scraps but he doesn't seem that bothered about fruit. What percentage of his diet is supposed to be made up of fruit and veg? —Preceding unsigned comment added by 84.64.109.187 ( talk) 08:27, 21 December 2007 (UTC)
I have an assingnment on manufacturing that goes like this:
You are requested to draw up a basic work scheme for the production of a functional
shaft, plain bearing and wheel assembly which is going to be used for a skateboard
undercarriage.
Plain bearing Shaft Wheel The plain bearing is fixed to the wheel and it rotates freely on the shaft. In your report identify; The materials which can be used for the three individual parts The manufacturing techniques and procedures to manufacture the parts Any post manufacture surface treatments to reduce wear and increase lifetime It is suggested to back your choices with relevant information
Can anyone direct me to appropiate sites where a good general idea can be given? P.S. I would like to construct the elements out of organic materials if possible. —Preceding unsigned comment added by 193.188.46.254 ( talk) 09:17, 21 December 2007 (UTC)
Why re-invent the wheel? Heh. No, seriously. The specifications and designs for skateboard wheels (and just about everything else that is manufactured) are covered already by
standards. The trick is to find the standard that will cover what you're looking for. Here's how to do this. There are numerous organizations out there that publish standards, depending on what their focus is. So, for instance the organization
ASTM is one, as is the
ANSI,
DIN,
IEEE,
BSI and other organizations. It would be quite difficult (unless you already knew) which of these organizations would be the one that would publish a standard that you're looking for. Fortunately, there's a private company called
ILI Standards that keeps an updated database that indexes all of the Standards in the world - or pretty close to all of them. I don't know what "ILI" stands for - nobody knows (or at least nobody that I know knows).
Now here's where it gets tricky. This company makes its money by selling standards that they print. Because of this they do not make the standards freely available online or anywhere else - they're very fussy about that. You either have to purchase one of their standards (which can actually be expensive), or try to find the standard you're looking for in some library. It is often difficult to know whether a particular library has the standard you're looking for; quite often libraries do not list the standards they have in their collection in their online catalogs. Instead, you need to contact the library's Reference Desk directly and ask if they have "such and such standard" in their collection. If they have what you're looking for, you can go make some photocopies of the pages that cover what you're interested in doing. The standards will describe what type of materials need to be used, they'll often provide diagrams and blueprints for the design, and they'll give specifications for tensions stresses, etc.
Only some libraries collect standards, of course. The best libraries to look for standards are ones that support some kind of research involving manufacturing, engineering, design, etc. So libraries that are associated with universities that offer degrees in these subjects would be good places to look for standards. I do not know of any library that has all of the standards in the world - standards cost a lot of money, and unless the library staff that orders the standards feels that there would be a need for a particular standard, it is unlikely that they would spend their often limited resources on purchasing standards to put in their collection if they believed that they would never be used by anyone. What you're looking for is a standard for skateboards, and quite frankly this is not one of those things (I'm guessing here) that would be included in a lot of libraries. It might be tricky to find a library that has the standard you're looking for. To make things worse, libraries do not ship standards from one library to the next through their Inter-Library Loan system. This is due to copyright restrictions on them. So if you're lucky you might find a library close to you that has the standard you're looking for. Then you can go and make photocopies for free. Otherwise, in order to get the standard, you're going to have to pay for it.
ILI Standards has an online database where you may search for what you're looking for; it's called ILI Infobase. I did a cursory search using the word "skateboard" and came up with this standard:
Standard Number: BS 5715(1993)
English Title: SPECIFICATION FOR SKATEBOARDS FOR RECREATIONAL AND SPORTS USE
Version Date: 03/15/1993
Country: United Kingdom (GB)
Summary: Specifies requirements for non-motorized skateboards which are supplied as complete articles for use by a single rider at a time. Coverage includes definitions, performance, marking, and design and construction. Also includes annexes and diagrams.
Committee: TCM/56
Publisher: BSI (BRITISH STANDARDS INSTITUTION)
389 CHISWICK HIGH ROAD
LONDON
W4 4AL
Table of Contents:
Committees responsible
Foreword
Specification
1 Scope
2 Normative references
3 Definitions
4 Design and construction
5 Performance
6 Advice to users
7 Marking
Annexes
A Skateboard safety code
B Advice on maintenance and use
C Schedule of tests
D Wheel friction test
E Speed test
F Endurance test
G External design
H Drop test
J Impact test
K Pulsating force test for deflection of metal decks
Figures
1 Major components of a skateboard
2 Radiusing of edges of deck
D.1 Diagram of friction test apparatus
F.1 Diagram of endurance test apparatus
G.1 Example of use of test cylinder
H.1 Diagram of apparatus for drop test
K.1 Diagram of arrangement for pulsating force test
List of references
Although this standard has been superceded by another (BS EN 13613), the newer standard seems to focus not on the "nuts and bolts" of the construction of the wheel assemblies of skateboards, but is more focused on safety issues. So I would use the standard I've quoted to find diagrams and descriptions of wheel assemblies. I hopt this helps. -- Saukkomies 08:30, 21 December 2007 (UTC)
The latest propaganda campaign by the Australian Government is that all sun-tanning is extremely dangerous and that you absolutely should not tan.
The campaign also tries to explain that we get enough Vitamin D from foods, that even though you feel and look healthier with a tan the risks are not worth it.
You can view the TV ad here:
http://www.darksideoftanning.com.au/campaign/tvc.aspx (the government has launched a whole website and media campaign against tanning
Is this paranoia or is well-founded truth? Previously I had asked on the reference desk about tanning, and discovered it's the UV rays that actually convert the Vitamin D and give you a tan. I also know it kills bacteria on the skin, and the sun helps you sweat, increases blood flow and has other benefits. Should I avoid the sun completely or is this campaign absolute nonsense to scare the masses into subjection?
Rfwoolf (
talk)
11:48, 21 December 2007 (UTC)
Well, what the ad campaign fails to clarify, is what if you're not part of the pale-white caucasion section of the population? What if you have a natural olive-brown skin and can in fact tolerate a bit of suntan? Well then their ad campaign would still have you believe that tanning is still 100% out of the question. As to why this is "propaganda", it's obvious that it does its best to illicit fear and other emotional responses in order to get people to take action. In a hypothetical case tanning would become taboo, and any individual that dares to go to the beach and lie in the sun would have dozens of people pointing at them and saying "haven't you hear? You're about to get cancer". The ad fails to offer any balance - the balance is that certain skin tones are more susceptable to skin cancer than others, and that if you have a darker skin tone you can tan for longer periods or spend more time outdoors. That's the clarification I'm after. Because I have a darker skin tone I'm definitely going to be spending some time tanning, no thanks to this blatant shock-campaign. Rfwoolf ( talk) 08:08, 22 December 2007 (UTC)
I've been wondering for a while why (to my knowledge) carnivores are not eaten anywhere on the world. I know some cultures eat dogs, but these are not obligate carnivores...brown bears are eaten, but they are omniovorous, and I have never heard of polar bears being eaten. We do eat carnivorous fish, reptiles and birds, so it seems to be restricted to carnivorous mammals. Is it just because they would not taste good, or would it be unhealthy to eat carnivores? And if the latter, why? -- Ferkelparade π 12:20, 21 December 2007 (UTC)
We do eat lots of different carnivores. Most of the fish we eat are carnivorous, for instance. However, there's a problem with eating mammalian carnivore species - it has to do with the buildup of toxins (and even good things) in the internal organs and tissues of carnivores. Toxins are concentrated in the bodies of animals (and humans) the further one goes up the food chain. One of the most pernicious substances, though, is actually
Vitamin A, which builds up in carnivores' livers and other organs - but especially livers. People
will die or get very very sick if they eat too much Vitamin A. An example is the story of
Xavier Mertz, an Antarctic explorer, who died after eating the liver of his sled dogs. So maybe as a result of this human societies developed
food taboos regarding the eating of carnivores. --
Saukkomies
08:45, 21 December 2007 (UTC)
The obvious answer is, it wouldn't be practical. What we are trying to do is get energy. Where does this energy come from? The sun. But we can't absorb that energy directly, so we have to use intermediaries to get that energy. We can eat plants, or animals that eat plants. But why would we want to eat animals that eat animals that eat plants? Cut out the middle man, it's inefficient. It would be pointless to raise carnivores to eat them, because them we have to also raise herbivoirs to feed the carnivores. But we can just eat the herbivores directly ourselves. It's more cost and energy efficient that way. Also like someone else said, we do eat some carnivores, in the form of fish, but no one is raising those fish. We just pluck them from the trees so to speak. We don't have to provide their food source, like we would with farm animals. Also we can't consume their food source either, well at least no one would want to on a regular basis. 64.236.121.129 ( talk) 17:36, 21 December 2007 (UTC)
Cats are obligate carnivores, and according to cat meat, are eaten in certain parts of the world. So the basic premise that carnivorous mammal meat is never eaten is untrue. I think the other responses give good reasons why it is not widely eaten (e.g., inefficient use of resources in farmed animals; concentration of toxins and prevalence of parasites in wild animals). -- Coneslayer ( talk) 17:58, 21 December 2007 (UTC)
MyD88-/- mice were generated as described and backcrossed for 9 generations on an H-2d (BALB/c) background. - what's the backcrossing necessary for? -- Seans Potato Business 20:15, 12 December 2007 (UTC)
That's weird...we answered this question on Dec 12th. What's it doing back here again? The OP's signature is even from Dec 12th. SteveBaker ( talk) 21:04, 21 December 2007 (UTC)
It seems that professors will often tell stories or use examples that just are not true. The story I have the biggest problem with is about slack action in trains. It goes something like this --It is impossible for a locomotive to start a 50 car train if all the slack is taken out. (ie the train in stretched) Therefore the engineer must back up his locomotive and bunch up the slack. Then he can move the train because he only has to pull one car at a time like 1,2,3,4,5 and so on." This is simply not true. How does the engineer start the train. He gets 6 locomotives with 6000 HP each for a total of 36000 Horsepower and he hooks it up to a 100 car train and with no slack in it just gives it hell and it will pull that coal train like there is no tomorrow. Locomotives have so much power that if an engineer were to follow the teachings of the professor he or she would lose their job because they would rip train apart from the jolt of the slack action.
Why then is this still taught? —Preceding unsigned comment added by 66.228.239.18 ( talk) 18:50, 21 December 2007 (UTC)
6 locomotives is indeed a bit much, the BNSF coal trains that pass through my town routinly have 3-4 units and they are always the newest- SD70ACe, or somtimes GEVOs from General electric. Either way both types are in the 4000 HP range and they handle the 15000 ton trains with ease. Secondly on the artical about diesel locomtives it states "the electric drive system is designed to produce maximum traction motor torque at start-up, which explains why modern locomotives are capable of starting trains weighing in excess of 15,000 tons, even on ascending grades. Current technology allows a locomotive to develop as much as 30 percent of its loaded driver weight in tractive force, amounting to some 120,000 pounds for a large, six-axle freight (goods) unit. In fact, a consist of such units can produce more than enough drawbar pull at start-up to damage or derail cars (if on a curve), or break couplers (the latter being referred to in North American railroad slang as "jerking a lung"). Therefore, it is incumbent upon the engineer (driver) to carefully monitor the amount of power being applied at start-up to avoid damage. In particular, "jerking a lung" could be a calamitous matter if it were to occur on an ascending grade." This being said it appears taht the professor's assertion is incorrect as there is acctualy more than enough power avalible. —Preceding unsigned comment added by 66.228.239.18 ( talk) 20:32, 21 December 2007 (UTC)
Good points all of them. However as part of the thought experiment goes the fuel consumption is no object to the professor. The professor states that it is physicaly impossible to move a 15000 ton train that has been streched out. I would have no problem with taking the professor to the local railroad yard and watching them start the trains. I've never heard slack action on a priortiy coal train... —Preceding unsigned comment added by 66.228.239.18 ( talk) 21:01, 21 December 2007 (UTC)
If I'm in a fast-food line, is it okay to shift my automatic car into neutral for like a minute or so? I'm trying to save gas, but I don't want to mess up my engine. 71.218.36.45 ( talk) 20:03, 21 December 2007 (UTC)
But, I've heard turning the engine on and off also wastes gas. 71.218.36.45 ( talk) 20:15, 21 December 2007 (UTC)
Ok, I don't have a Mini or a Prius. I have a 2004 Hyundai Elantra. It is fuel injected, but I've heard it still wastes gas if you turn off the engine and quickly start it up again. Back to my original question, should I put my car in Neutral if I'm going to be waiting in line, or is Park better? 71.218.36.45 ( talk) 21:04, 21 December 2007 (UTC)
Which one is better? (please, reply only if you really have something meaningful to say) -- Taraborn ( talk) 20:10, 21 December 2007 (UTC)
Something meaningful to say : You need both for a proper Baseball game. I'd say some combination of the two is appropriate for most situations. APL ( talk) 01:11, 22 December 2007 (UTC)
This concept of which is better - cooperation or competition - is the basis of the Nash Equilibrium theory that was named after John Forbes Nash, who won the 1994 Nobel Prize in Economics for it. Nash is also the real-life person that the movie A Beautiful Mind was based on. -- Saukkomies 02:30, 22 December 2007 (UTC)
Out of curiosity, how much would annual greenhouse gas emissions be cut down if everyone got fuel efficient cars? Someguy1221 ( talk) 21:12, 21 December 2007 (UTC)
Globally, transportation fuels are about 14% of total greenhouse gas emissions. My recollection is that cars represent about half of that, with the rest goes to planes, trains, buses, and heavy trucks, etc. So lets call it 7% of the global total. You need to estimate current average fuel economy and compare that to some guess for how things will improve. The corporate average fuel economy standards in the US, which are among the most lax in the world, require the current fleet of cars to average at least 27 miles per gallon (or 21 for SUVs and light trucks). In practice, existing cars are nearly always worse than that because efficiency tends to decline with age. For the sake of argument, lets pessimistically say that all the cars still in operation really only average 15 miles per gallon. If you replace them all with Priuses which have a real world performance of ~45+ miles per gallon, then you'd shave off as much as 2/3 of that 7% of the total gas emissions. In other words, replacing all the cars might (optimistically) net you as much as a 4.5% reduction in total greenhouse gas emissions. Assuming your don't increase the total number of cars in operation, or the amount that people are driving, etc. Dragons flight ( talk) 23:29, 21 December 2007 (UTC)
Why is the meat inside a cornish pasty and certain sausage rolls grey? -- Seans Potato Business 21:28, 21 December 2007 (UTC)
What is the source of the energy in this device? I dont think its the gravity... 79.176.187.141 ( talk) 23:48, 21 December 2007 (UTC)