Wikipedia:Reference desk/Archives/Science/2011 September 11

= September 11 =

Bones made of strontium instead of calcium?
If I were to take 3.7 grams of strontium carbonate every day and stop eating dairy products, would all the calcium in my bones and teeth eventually be replaced by strontium? Count Iblis (talk) 00:45, 11 September 2011 (UTC)
 * No. 67.169.177.176 (talk) 04:31, 11 September 2011 (UTC)
 * To expand a bit, it is pretty clear that the human body can tell the difference between two elements with the same valency, for example sodium and potassium are readily distinguishable (see Na+/K+-ATPase for but one example), so I don't see why the processes which use calcium couldn't readily distinguish it from strontium. -- Jayron  32  04:37, 11 September 2011 (UTC)
 * The article on strontium indicates it can indeed be used by the body as if it were calcium. At least one problem there is the risk of acquiring too much strontium-90, which would kill its recipient well before all his bones became all-strontium. I also suspect that it would be very difficult to entirely avoid getting at least some calcium in one's diet. ←Baseball Bugs What's up, Doc? carrots→ 04:43, 11 September 2011 (UTC)
 * Well, there you go. -- Jayron  32  04:46, 11 September 2011 (UTC)
 * Also, the human body uses calcuim for other stuff besides bones -- muscle contraction, for instance, as well as transmission of nerve impulses. An extreme level of calcium deficiency (such as that which would be required to replace all, or even most, of the calcium in the bones with strontium) would send you into fatal cardiac arrest long before a significant portion of the calcium can be replaced, and prob'ly even before you get a lethal dose of strontium-90. 67.169.177.176 (talk) 04:58, 11 September 2011 (UTC)
 * The opposite (if the question was if they will get stronger). High doses of strontium causes rickets, also known as osteomalacia in adults, the weakening of the bones due to inadequate amounts of calcium. Strontium seems to help bone growth by acting as a 'primer' (an agonist) somewhat, encouraging the maturation of osteoblasts while suppressing osteclasts (the body mistakes it for calcium). But calcium is still required for the bulk of the growth. When strontium levels are too high, the body has problems absorbing calcium resulting in hypocalcemia and thus osteomalacia. Osteomalacia is usually documented in patients with renal failure (it may actually cause the condition) and the subsequent inability to excrete strontium leading to a buildup (strontium is normally excreted at higher rates than calcium, up to three times I think).--  Obsidi ♠ n   Soul   04:52, 11 September 2011 (UTC)


 * No. The question makes the erroneous assumption that you can eliminate calcium from your diet by eliminating all dairy products.  That's not even approximately true.  There's plenty of calcium in other foods as well, as should be obvious considering that humans didn't even start regularly consuming the milk of other animals until the most recent 4% of the time that anatomically modern humans have existed.  Red Act (talk) 08:15, 11 September 2011 (UTC)

Thanks everyone for explaining! Count Iblis (talk) 18:15, 11 September 2011 (UTC)

How to "open" a penny
Is there any way to "open" a penny and separate the copper coating from the zinc? --76.211.90.74 (talk) 02:41, 11 September 2011 (UTC)
 * Zinc will dissolve in an acidic solution of hydrochloric acid. You can take a file and cut notches in the sides of the penny, then place it overnight in some hydrochloric acid.  When you come back, you'll have a copper shell.  -- Jayron  32  03:30, 11 September 2011 (UTC)
 * You can also file a little copper off the edge of the penny and use tongs to hold the penny over a hot flame (such as a natural gas flame). Zinc melts at a lower temperature than copper, and when the penny reaches this temperature the zinc will flow out through the hole in the copper. Make sure you have something ready to catch the molten zinc. —Bkell (talk) 05:01, 11 September 2011 (UTC)
 * Just in case anyone outside the USA reads this and is tempted to try it, the method applies to the Penny_(United_States_coin), not the British Penny, or to pennies in many other countries where there is no zinc inside. The British penny is now copper-plated steel, so it is ferromagnetic.    D b f i r s   07:19, 11 September 2011 (UTC)


 * Readers and editors should be aware that in at least some countries (apparently including the US) defacing or destroying currency is illegal. I know it's only a penny, but on principle, I think we should at least be aware of the legal potential. Mitch Ames (talk) 11:01, 11 September 2011 (UTC)
 * Our Elongated coin suggests (although it appears to be unsourced wp:Syn) it may not be illegal in the US if there is no intention to defraud or profit from the metal. Nil Einne (talk) 11:24, 11 September 2011 (UTC)


 * How much easier is it to fraudulently fabricate small change, as opposed to paper money? Plasmic Physics (talk) 13:14, 11 September 2011 (UTC)


 * The point is not to fabricate change, but to melt it and sell the copper for a profit. Dauto (talk) 13:39, 11 September 2011 (UTC)

Is there any way to keep the zinc? --76.211.90.74 (talk) 15:04, 11 September 2011 (UTC)
 * In Nigeria they used to have a tenth of a penny coins with a hole in the centre. A person was cautioned about defacing them as he used a large number as washers - they were cheaper and better than the proper ones. Dmcq (talk) 17:07, 11 September 2011 (UTC)


 * Vaguely related to the above - any truth to the story that people took to wiping their backsides with Zimbabwean dollars - as the banknotes were worth far less than the equivalent volume of toilet paper and were more widely available? I know that people definitely took to burning them instead of using them to buy fuel... --Kurt Shaped Box (talk) 21:14, 11 September 2011 (UTC)


 * In Russia in the 1990's (a period of hyperinflation), they used to use one-ruble bills to insulate apartments in the winter. 67.169.177.176 (talk) 03:59, 12 September 2011 (UTC)

Laser hazard?
If i was to create a 30kV spark gap by mounting two 1cm brass spheres 1cm apart, and passing about 1kA through it, would there be any danger of inadvertently creating an atmospheric pressure uv laser and dangerous levels of uv radiation??--78.150.237.136 (talk) 10:54, 11 September 2011 (UTC)


 * A thousand amps will produce an enormous amount of heat. I'm not sure how much UV light you will produce, but you will certainly be in danger from flying molten metal!    D b f i r s   14:34, 11 September 2011 (UTC)


 * You would also run the risk of legal trouble from your country's radio communication authorities due to the massive broadband noise signal your spark gap will generate. Roger (talk) 16:04, 11 September 2011 (UTC)


 * Not to mention the chance of accidental electrocution. 67.169.177.176 (talk) 23:20, 11 September 2011 (UTC)


 * An electric arc does not have to involve any laser to create hazardous amounts of UV. Arc welders are at risk of "arc eye" or Photokeratitis, a painful and dangerous eye inflammation or blindness caused by exposure to the electric arcs used in welding, and to other UV sources. This can happen at lower currents and far lower voltages than you describe. Edison (talk) 04:24, 12 September 2011 (UTC)

OK, but will i get any laser action?--78.148.140.132 (talk) 08:28, 12 September 2011 (UTC)
 * How long do intend to operate the spark gap? You are talking about 30 megawatts of power here.  Googlemeister (talk) 15:08, 12 September 2011 (UTC)
 * ... only if the 30kV is maintained. Usually, the voltage is drastically reduced once the air is ionised and the 30kV is generated only to get the spark started.  The situation described is obviously unrealistic for a normal laboratory, but perhaps the OP is diverting the output from a power station?  I wonder if 1kW rather than 1kA was intended?    D b f i r s   17:25, 12 September 2011 (UTC)


 * No. Without a mirror and partially silvered mirror, there is no resonance chamber to produce the population inversion necessary for laser light. 69.171.160.155 (talk) 17:39, 12 September 2011 (UTC)

The experiments were performed many years ago. The sparks lasted less than 1 microsecond and at about 10 Hz rep rate. The peak pulse current was indeed 1kA and the sparks were very noisy. When the arc struck there would have only been a few hundred volts across the gap. Trouble is, we did not allow for the possibility of creating laser light in the safety assessment becuase we were not aware of it. Should we have been aware? And how much laser ligh,t if any, was likely to have been emitted.--89.243.135.86 (talk) 21:10, 12 September 2011 (UTC)

psychology of money
Are people who base their self esteem or their social esteem on their financial worth subject to a setback in self esteem or social esteem when they encounter people with more money? --DeeperQA (talk) 11:21, 11 September 2011 (UTC)


 * From your wording of the question, it seems obvious that they would.--78.150.237.136 (talk) 11:30, 11 September 2011 (UTC)


 * So conversely a person who suffers a setback in self esteem or social esteem following an encounter with someone with greater financial worth could be a person who bases their self esteem or social esteem on financial worth? --DeeperQA (talk) 15:39, 11 September 2011 (UTC)


 * Or they may be inspired. StuRat (talk) 15:38, 11 September 2011 (UTC)


 * I assume you mean inspired to increase their financial worth? --DeeperQA (talk) 15:42, 11 September 2011 (UTC)


 * In a Keeping up with the Joneses fashion. --Mr.98 (talk) 18:32, 11 September 2011 (UTC)


 * Yes, and beyond inspiration, they might get some specific ideas of how to enrich themselves ("first, get some politicians in your pocket, then..."). StuRat (talk) 20:16, 11 September 2011 (UTC)


 * It was so cold yesterday, I saw a lawyer with their hands in their own pockets. Plasmic Physics (talk) 23:07, 11 September 2011 (UTC)

Nicotine and dogs behaviour
Have there been any studies on the behaviour effects of nicotine in dogs? I know that beagles were used a lot in research on cigarettes, but that seems to be just the physical effects. --TammyMoet (talk) 14:15, 11 September 2011 (UTC)
 * Well, there is quite a bit of evidence that nicotine has rewarding effects on dogs just as it does on humans, see for example.  Is that the aspect of behavior you are interested in? Looie496 (talk) 15:15, 11 September 2011 (UTC)
 * Any aspect really.--TammyMoet (talk) 16:30, 11 September 2011 (UTC)

Well, it makes them look way cool and attracts dogs of the opposite sex.Gzuckier (talk) 05:31, 12 September 2011 (UTC)

We use only 10% of our brain?
This is false right? Where does this myth come from? Why do people say we only use 10% of our brain? ScienceApe (talk) 15:55, 11 September 2011 (UTC)


 * We actually have an article about this: 10% of brain myth.  The most interesting thing about it is that nobody has ever figured out where the myth originated (although there are a variety of speculations). Looie496 (talk) 15:59, 11 September 2011 (UTC)


 * I suspect that this was because only 10% of the function can be easily identified. Like other biological functions, a good portion of the brain seems to be used for "behind the scenes" tasks we don't always consider.  For example, analysis of dreaming gives us some insight that memories need "post processing" to  better organize themselves into rules for future action.  People who work with computer databases will recognize this pattern, since such maintenance is also required there.  StuRat (talk) 16:03, 11 September 2011 (UTC)


 * Of course the opposite theory (that IQ is all about brain size) was delightfully taken apart by Stephen J Gould. FWIW I think it might be to do with Phineas Gage. Having a steel bar rammed through your head and losing half a cup of fresh brain leaves you still able to walk, talk and have a cup of tea. In the heady Victorian days when Mr Gradgrind deliberated that would have been a form of proof. Certainly the belief has been around for a long time --BozMo talk 16:42, 11 September 2011 (UTC)


 * It seems to have been propagated in modern times by mystics, psychics and the like to explain their profound powers (claiming that they can tap into this percentage of the brain others cannot). Uri Geller reportedly has made this claim (ref). I also remember it being used in many novels and films as a storytelling device to explain characters' extra-human powers; I can't recall particular examples but did Stephen King use it to explain Danny's gift in The Shining (novel)?  Jebus989 ✰ 17:52, 11 September 2011 (UTC)


 * I always thought about it in a metaphorical sense: we use 10% of our intellect, which could be true. Quest09 (talk) 22:44, 11 September 2011 (UTC)


 * What is "intellect"? That always seems like one of those ephemeral concepts like "soul" and "conscience" and the like which doesn't seem all that quantifiable.  How can one use ten percent of a concept which is so fuzzily defined that we can't even know what 100% would look like?  -- Jayron  32  03:56, 12 September 2011 (UTC)


 * You are right: intellect is not so well-defined as temperature, and consequentially it cannot be measured in the same way. However, let's think of the 10% of our brain as a motivational motto, something like creativity is 1% inspiration plus 99% transpiration. Only someone in the autistic spectrum would ask seriously how did you measure that? Quest09 (talk) 12:04, 12 September 2011 (UTC)
 * And a biologist would ask why only plants can be creative 99% of the time. Googlemeister (talk) 19:53, 12 September 2011 (UTC)
 * And a plant neurobiologist will say see, I knew plants had 1% neurological activity. Quest09 (talk) 20:41, 12 September 2011 (UTC)
 * I think there is a major misconception with this myth which I can only explain by analogy: It's like saying you only use 20% of a car to drive, sure you can take bits out and barely notice, but you also can't expect the seats to give you extra horse power. Vespine (talk) 04:22, 12 September 2011 (UTC)

Personally, I think its an average; 90% of people don't use any of their brain, so on the average....Gzuckier (talk) 05:30, 12 September 2011 (UTC)
 * HA! I like yours better:) Vespine (talk) 06:31, 12 September 2011 (UTC)
 * I always interpreted that as people only use 10% of their brain at any given instant (only 10% of neurons would be shown as firing for any particular nanosecond). That is not the same thing as only 10% gets used.  Googlemeister (talk) 13:42, 12 September 2011 (UTC)
 * I doubt there is a stable amount of neuron being fired. As I stated above, I would be surprised if any literal interpretation were true. Quest09 (talk) 14:46, 12 September 2011 (UTC)

Cola or vinegar as cleaner for hard water scale
Between diet cola and vinegar, which is more effective as a non-toxic cleaner of hard water scale? --108.36.90.144 (talk) 17:21, 11 September 2011 (UTC)


 * Could you be more specific about "vinegar"> there are rather a lot of types of widely varying composition... --BozMo talk 17:58, 11 September 2011 (UTC)


 * White vinegar, the kind that you can get from almost any grocery stores. --108.36.90.144 (talk) 18:14, 11 September 2011 (UTC)


 * The vinegar article gives its Ph as "2.4 to 3.4" (which is quite a wide range). This page lists the Ph of several diet soda drinks, which are in the 2.4 to 2.8 range. So, without testing your specific vinegar, they're about the same. Now comparing prices: Tesco's generic malt vinegar costs £0.78/litre; their generic diet cola costs £0.27/litre, and the name brand Diet Coke costs £0.89/litre. -- Finlay McWalterჷTalk 19:49, 11 September 2011 (UTC)


 * And that sounds like a far better use of soda than drinking it. StuRat (talk) 20:12, 11 September 2011 (UTC)


 * How about a concentrated hot saline solution? Plasmic Physics (talk) 23:03, 11 September 2011 (UTC)
 * Heating your cleaning solution would be good, but a saline solution is probably the last thing you want. The more salt there is in your solution, the less of the salts in the scale it will be able to pull into solution. Acids will work best.  — Preceding unsigned comment added by 72.94.166.193 (talk) 23:09, 11 September 2011 (UTC)


 * OK, not concentrated then. Acid is always good, but you don't want to be damaging the underlying surface. Plasmic Physics (talk) 23:39, 11 September 2011 (UTC)


 * The point is that limescale is mostly calcium carbonate, which dissolves well with even relatively weak acids but dissolves very little at neutral or higher pH. Vinegar is a commonly recommended treatment for hard water residues.  Obviously one should test any treatment on the surface to be sure it won't be damaging.  Dragons flight (talk) 01:58, 12 September 2011 (UTC)

Clock on moon
If someone placed a clock on the moon will it run faster or slower or equal the speed of clock on earth? — Preceding unsigned comment added by 175.110.242.217 (talk • contribs) 18:48, 11 September 2011 (UTC)


 * Take a look at the Twins paradox article for your particular problem, and the time dilation and special relativity articles for a more comprehensive study. — Fly by Night  (  talk  )  18:56, 11 September 2011 (UTC)


 * I don't believe there would be any measurable difference. StuRat (talk) 20:10, 11 September 2011 (UTC)


 * See our article on the Hafele–Keating experiment. — Fly by Night  (  talk  )  20:53, 11 September 2011 (UTC)


 * Yep. Amazingly, the atomic clocks these days are quite capable of demonstrating the effect of general relativity due to gravity just from different altitudes on earth, so you'd absolutely expect the effect of lowering the gravity to the moon's to be obvious. Gravitational_time_dilation Gzuckier (talk) 05:29, 12 September 2011 (UTC)


 * Gravitational time dilation is a big enough effect that making gravitational time dilation corrections due to the difference in clock speed between the Earth's surface and medium Earth orbit is essential for maintaining the accuracy of the GPS system. Without corrections for gravitational time dilation, errors would accumulate at a rate measured in kilometers per day!  See Error analysis for the Global Positioning System.  Red Act (talk) 17:25, 12 September 2011 (UTC)


 * Faster by roughly a factor of 1 + 7*10^(-10), due to the difference in the gravitational potential which is the dominant effect here. Count Iblis (talk) 21:02, 11 September 2011 (UTC)


 * That's about a second every 45 years, much more than I would have expected. StuRat (talk) 01:06, 12 September 2011 (UTC)


 * That's an interesting answer, but what's the reason behind it? Is it because gravity will make the bits and pieces of the clock more massive, which will in turn slow down the clock's workings. Is it connected to special relativity and, if so, how does gravity relate? Could you link to some articles? I'd be interested to look at that more. — Fly by Night  (  talk  )  21:11, 11 September 2011 (UTC)
 * It's relativistic time dilation. See Gravitational time dilation. --Tango (talk) 21:34, 11 September 2011 (UTC)


 * &hellip;Thanks Count Iblis. — Fly by Night  (  talk  )  22:14, 11 September 2011 (UTC)

It's of course more fun to derive the answer from first principles. In the weak field approximation the metric is:


 * $$ds^2 = c^2 \left(1+2 \frac{V(r)}{c^2}\right)dt^2 - dl^2$$

where dl^2 is the Euclidian spatial part of the metric and V(r) is the gravitational potential. You can use this metric to derive all the special relativistic effects due to time dilation and the general relativistic effects due to gravity in the weak field limit.

The quantity ds^2 is the invariant distance in space-time between two events. In the absense of gravity, if someone is moving with velocity v in your frame, you have in your frame: dl = |v| dt, so the space-time interval between points dt in time apart is given by ds^2 = (c^2 - v^2)dt^2. This is an invariant, so the person who is moving w.r.t. you will find the same value for ds. Since this person is not moving in his own frame, the spatial separation between the two events is zero and he find that ds^2 = c^2 dt'^2, where dt' is the time difference according to him. Equating the two expressions for ds yields the famous time dilation formula: dt = dt'/sqrt(1-v^2/c^2).

If you have weak gravitational fields, then the global metric is given by the above formula for ds^2. An observer, using his clock and ruler to define distances and time intervals in his immediate neighborhood will find that special relativity holds as usual, so ds^2 = c^2 dt^2 - dl^2.

Then if we have clock on the Moon, two ticks of that clock in the rest frame of the clock a time dt' apart corresponds to ds^2 = c^2 dt'^2. If we ignore the motion of the clock relative to Earth, then in the global coordinate system, the same space-time interval is given as ds^2 = c^2 (1 + 2 V(r')/c^2)dt^2, where r' is the position of the clock so V(r') is the gravitational potential at the location of the clock. So, we have:


 * $$dt = \frac{dt'}{\sqrt{1+2\frac{V(r')}{c^2}}}$$

Then if we send the two ticks of the Moon's clock to Earth, then these two ticks will arrive with the same time delay, so well receive two signals separated in the global time coordinate by the same dt as given by the above formula. The space-time interval between these two events here on Earth is given by ds^2 = c^2 (1+2 V(r")/c^2) dt^2, where r" is the positon on Earth where the two signals are received and V(r") is then potential there. Then a clock here would measure a time difference dt" for these two signals such that ds^2 = c^2 dt"^2. Therefore we have:


 * $$dt' = \sqrt{\frac{(1+2 \frac{V(r')}{c^2})}{1+2\frac{V(r)}{c^2}}}dt\approx \left(1 + \frac{V(r') - V(r)}{c^{2}}\right)dt$$

Taking into account the Earth's and the Lunar gravitational potential, you then find a time dilation factor dt'/dt" of 1 + 6.525*10^(-10). The gravitational potential of the Sun also contributes. At full Moon, you have to add 2.533*10^(-11) to the time dilation, while at new Moon you have to subtract 2.546*10^(-11). The contribution due to the relative velocity of the Moon w.r.t. the Earth depends on the position of the observer on Earth. At the equator, when the Moon is overhead, this makes a contribution of minus 1.7*10^(-12). Count Iblis (talk) 03:34, 12 September 2011 (UTC)

Most useful element
Which element is the most useful? --76.211.90.74 (talk) 19:02, 11 September 2011 (UTC)


 * How long is a piece of string? Well, it depends what you want the string for. — Fly by Night  (  talk  )  19:08, 11 September 2011 (UTC)


 * Oxygen, carbon and hydrogen are pretty handy, I suppose  Jebus989 ✰ 19:09, 11 September 2011 (UTC)


 * Yes, with many elements being absolutely essential to our survival, there's no way to distinguish the usefulness of one from the other. To this list we can add iron, nitrogen, calcium, potassium, phosphorus, sulfur, magnesium, manganese, sodium, copper, zinc, selenium, molybdenum, fluorine, chlorine, iodine, cobalt, etc. StuRat (talk) 20:01, 11 September 2011 (UTC)


 * The element of chance, opportunity.190.56.107.43 (talk) 19:44, 11 September 2011 (UTC)


 * Unobtanium has countless uses, and is irreplaceable. DuncanHill (talk) 20:02, 11 September 2011 (UTC)


 * Hydrogen, it can give rise to stars, planets, humans, computers, cities etc. etc. all by itself. Count Iblis (talk) 20:16, 11 September 2011 (UTC)

I guess what I meant was, "Which element is the most useful in industry/technology?" --76.211.90.74 (talk) 20:46, 11 September 2011 (UTC)


 * Silicone, probably. Computers and that. --Kurt Shaped Box (talk) 21:07, 11 September 2011 (UTC)
 * I expect you mean Silicon rather than Silicone. Grandiose (me, talk, contribs) 21:25, 11 September 2011 (UTC)
 * Na. Women with breast implants make this terrible world that little bit more bearable. --Kurt Shaped Box (talk) 22:11, 11 September 2011 (UTC)
 * I lolled.--  Obsidi ♠ n   Soul   04:04, 12 September 2011 (UTC)
 * Plastic is quite useful and that's made of mostly hydrogen and carbon. --Tango (talk) 21:37, 11 September 2011 (UTC)
 * Iron is definitely one of the most useful elements, the others being copper and aluminum. 67.169.177.176 (talk) 23:22, 11 September 2011 (UTC)
 * I gotta go with hydrogen, since hydrogen atoms like to clump together on their own and become factories. --Goodbye Galaxy (talk) 17:27, 12 September 2011 (UTC)

Gold or platinum: you can sell it and buy what's useful.Quest09 (talk) 20:50, 12 September 2011 (UTC)
 * You can sell iron and buy what is useful too, you just need more of it. Googlemeister (talk) 13:38, 13 September 2011 (UTC)


 * You can also use the iron to get what you want directly. --Carnildo (talk) 01:36, 16 September 2011 (UTC)

Engines
Let's say that I had two engines. One with a single cylinder with a one litre displacement, and the other with ten cylinders with 1/10 of a litre displacement each. Both are 1000cc engines, but both should have different properties. Does anyone have any idea as to what the differences would be? There will be differences in terms of horse power and torque. What would those differences be, and what would these differences be due to? Thanks in advance. — Fly by Night  (  talk  )  19:07, 11 September 2011 (UTC)


 * I believe more cylinders is better, to a point, for both HP and torque, since it allows for more efficient combustion. (Of course, there is a limit, too many cylinders and the increased frictional forces will become an issue.)  Note that this is absolute power and torque I'm talking about.  When looking at the power-to-weight ratio, more cylinders aren't as beneficial, since they increase the weight quite a bit.  Of course, a single cylinder will also provide a rather rough "putt-putt" power, while a 10 cylinder engine will be nice and smooth.  Furthermore, if the single cylinder engine misfires, it will likely stall, unless there's some mechanism to keep it going, like a flywheel.  As for maintenance, the more cylinders, the more maintenance is needed, and the more time and money it will take.  For example, you need at least one spark plug per cylinder, which will occasionally require cleaning or replacement. StuRat (talk) 19:56, 11 September 2011 (UTC)


 * I'm not sure I agree. It depends on more factors, e.g. how highly the engine revs. Formula 1 cars only have 2.4 litre engines. They rev at 18,000&thinsp;rpm and develop almost 800&thinsp;hp, but don't have much more torque (≈&thinsp;250&thinsp;nm) than a conventional production car. Thanks for your reply but I was hoping for a more technical reply in terms of the physics and mechanics. — Fly by Night  (  talk  )


 * Well, yes, compression and revs figure in too, but we were only looking at number of cylinders, I thought. If you want to consider all factors in internal combustion engine design, then I suppose I should state that diesel engines typically produce more torque, but fewer HP, than gasoline engines.  StuRat (talk) 23:51, 11 September 2011 (UTC)


 * One cylinder gasoline "Hit-and-miss engines" were common in the early to mid 20th century, and can still be seen in operation at antique farm equipment museums and exhibition days. I saw one such a couple of years ago. Certainly it had a flywheel, since it would not have worked meaningfully without one. When spun to start, it would admit a gasoline-air mix to the cylinder, compress it, and then the spark plug or ignitor powered by a magneto or dry cell battery would fire at the proper time, accelerating the spinning flywheel. If the rotational speed was above the setpoint, as in an unloaded engine, then it might spin a number of times without the engine firing. When the speed dropped, it would admit gasoline and air and fire the sparkplug. An unloaded engine would thus fire one time out of several revs, but a fully loaded engine would fire on every rotation. The one I saw had as a cooling system simply a hollow in the top of the cylinder which was filled with water, which gradually boiled away. A modern lawnmower typically has a one cylinder engine with a magneto to fire the spark, and it fires on every rotation of the flywheel, which is the rotary blade. A one cylinder engine typically has more flicker, or more voltage variation during an engine cycle, than a multi-cylinder engine when it is driving a generator. Some old John Deere farm tractors had one cylinder, and worked this way, with a very distinctive sound. Edison (talk) 04:11, 12 September 2011 (UTC)


 * Well, one liter isn't big enough to show it, but you sound like you're looking for general principles, which would be more important with bigger volumes. One is that the speed of the flame front is constant no matter how big the engine; which means that with a very large cylinder size, top rpm is limited by the inability of the flame to spread through all the cylinder in time, so the one cylinder wouldn't be able to rev as high as the ten cylinder, even without any mechanical stress issues. Another issue is valve size. One cylinder of volume 10X compared to ten cylinders with the same proportions but with volume X would have valve size 10^(2/3) as large as each small cylinder to move 10 times the volume of air, which again limits top rpm by the drag of the air through the valves. On the other hand, you will see a benefit in low speed operation, since the comparatively smaller valve openings will cause more turbulence and mixing of the air/fuel leading to more complete combustion and perceived as greater low rpm torque; similar to what is well known with two cylinders of identical volume, one of small bore and long stroke, one with large bore and short stroke. There will be other issues with the limits to plain mechanical strength, since the con rods of the big engine will only have 10^(2/3) as large a cross sectional area, and thus only 10^(2/3) as much strength, while the piston will be 10 times as massive, unless you make it shallower from top to bottom, so the conrods will break at a lower rpm on the 1 cylinder engine; again, similar to the reason why elephants have thicker legs than deer. Gzuckier (talk) 05:22, 12 September 2011 (UTC)

Titanium alloy
What is the strongest and least dense titanium alloy? --76.211.90.74 (talk) 20:55, 11 September 2011 (UTC)
 * You can have some kind of lithium titanium alloy. Where the lithium predominates this would be very low density. You will not be able to optimise strength and density at the same time. Graeme Bartlett (talk) 06:41, 12 September 2011 (UTC)
 * You can optimize for the strength to density ratio though. Googlemeister (talk) 15:00, 12 September 2011 (UTC)
 * Would a lithium titanium allow have corrosion problems? RJFJR (talk) 18:18, 12 September 2011 (UTC)
 * In don't know about titanium, but we have some info on aluminium as a possible analogy. Our Al-Li article mentions several-percent-lithium alloy is used commercially in places where a corrosion-prone material seems unlikely to be used (aircraft and rocket bodies). That article also mentions that the addition of Li to Al (technically, replacing Al atoms with Li atoms in the matrix) decreases density (as one expects) but also increases strength. DMacks (talk) 18:31, 12 September 2011 (UTC)

Uranocene
How does the uranium bond to the (empty) center of the ring instead of to one or more of the carbons? --76.211.90.74 (talk) 23:02, 11 September 2011 (UTC)
 * The article says this happens because of interaction between the uranium atom's d-orbitals and the ligand's pi-bonds. In other words, the uranium actually bonds to ALL of the carbons at the same time. 67.169.177.176 (talk) 23:26, 11 September 2011 (UTC)
 * See also metallocene bonding. Rmhermen (talk) 01:05, 12 September 2011 (UTC)