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April 3

Newton's Second Law

Newton's second law says that F = ma. If there a[re] several forces f_i acting on a particle, then Σf_i = ma. Does this last rule -- that the resultant force is the vector sum of the individual forces -- follow from Newton's second law, or is it an independent law? 74.15.137.130 (talk) 03:26, 3 April 2011 (UTC)[reply]

I don't know that that is a law so much as a basic mathematical concept. It predates Newton by some several centuries, and I doubt he considered it more important dwell upon than any other basic mathematical concept. See Euclidean_vector#Addition_and_subtraction for the basics, but I am pretty sure the details of simple vector mathematics were commonly understood and part of mathematical canon by the time Newton came around. --Jayron32 03:44, 3 April 2011 (UTC)[reply]

I think F refers to net force. In other words, F = Σf_i. — DanielLC 03:52, 3 April 2011 (UTC)[reply]

It has to be shown, of course, that vectors (which add and subtract like that by definition) are actually a good model for forces, so that the mathematical concept of vector addition corresponds to the physical concept of superposition of forces. One might think of some sort of interference between two forces of different origin acting on the same body. I do not know how Newton dealt with that or whether he had given this point any thought at all. The section Euclidean_vector#History is hardly existent, but it appears that the concept of a vector essentially was developed after Newton. The German article mentions Hermann Grassmann, 1844. --Wrongfilter (talk) 07:16, 3 April 2011 (UTC)[reply]

This is a consequence of the fact that Newton's second law is a linear differential equation, and so, roughly speaking, you can break down the force F on the left hand side into components, solve for each component, then add the individual solutions together again to get a solution for F - see superposition principle. Many (or perhaps most) physical laws are non-linear (there is a long list in the non-linear differential equation article) and general explicit solutions are not so easily obtained. Gandalf61 (talk) 08:30, 3 April 2011 (UTC)[reply]

But it's usually done the other way around. If a point mass is in a gravitational field, it will feel a force F_g, producing an acceleration F_g/m. If you push on it with a force F, then the acceleration becomes (F_g F)/m. The fact that, no matter how many forces are acting on it, the net force can always be decomposed to include the gravitational force that would be present were there no other forces seems to be independent of Newton's Law. 74.15.137.130 (talk) 19:13, 3 April 2011 (UTC)[reply]

To be cleaner, we'll have to scrub ourselves from the inside-out too. How will we?

Sadly, the shower only cleans our outer shells. Yet in the meantime, metabolic filth keeps accumulating on our insides, causing us to visually age, get the old people smell, and eventually die from having too much of this inner filth.

In the future, what will be some ways to clean out the insides of our bodies? (And this would extend our life expectancies now would it?)

Until then, besides washlets, what are some ways to scrub ourselves from the inside-out in the present day? How well do they work, and will there be any side-effects? --70.179.169.115 (talk) 06:51, 3 April 2011 (UTC)[reply]

Enemas (Shakespeare's "clyster pipes") have been in use for centuries. We cannot give medical advice about effectiveness. I don't know whether there is any validity in the concept of death by "metabolic toxin". Dbfirs 07:57, 3 April 2011 (UTC)[reply]

Colonic irrigation. --TammyMoet (talk) 09:09, 3 April 2011 (UTC)[reply]

Eat enough vegetables, fruit, and wholemeal/wholegrain. See http://www.nhs.uk/livewell/5aday/pages/5adayhome.aspx/ 92.15.9.102 (talk) 09:28, 3 April 2011 (UTC)[reply]

In the future, we may use nanomedicine. Mitch Ames (talk) 09:57, 3 April 2011 (UTC)[reply]

You don't want your insides too clean. A healthy community of gut flora provide many essential services to the body. "The metabolic activities performed by these bacteria resemble those of an organ, leading some to liken gut bacteria to a "forgotten" organ." You could probably live without gut flora, but I'm happy to keep mine intact. SemanticMantis (talk) 14:31, 3 April 2011 (UTC)[reply]

Sounds like it's time for the great goldenseal debate... ;) no, I'm not saying it works for that... Wnt (talk) 17:24, 3 April 2011 (UTC)[reply]

Have we still not evacuated the washlet subject adequately for the OP yet? Cuddlyable3 (talk) 21:00, 3 April 2011 (UTC)[reply]

I'm not sure the idea of "inner filth accumulation" is really something supported by science. Maybe you should look into that a bit before you decide to "clean out your insides".. Our bodies are quite good at self regulating and self cleaning, unless you have something wrong with you, generally you only need to worry about the cleanliness of your outsides. Aging and "old people smell" isn't anything to do with inner filth that you could clean out, as far as I know it's ultimately related to telomerase shortening. Vespine (talk) 22:53, 3 April 2011 (UTC)[reply]

On the other hand, the notion that unspecified harmful substances routinely accumulate in the body and must/can be removed by means of some deliberate cleansing procedure is an ever-popular staple of medical pseudoscience. It must somehow resonate deeply with what people are prepared to believe. –Henning Makholm (talk) 23:16, 3 April 2011 (UTC)[reply]

There is such a thing as Bioaccumulation and I have never seen any evidence that humans are immune to it. Of course, you can't just scrub the mercury out of your system, but the I would expect that "unspecified harmful substances" do routinely accumulate in the human body just as readily as they do anything else. Falconus^{p t c} 12:57, 4 April 2011 (UTC)[reply]

Isn't this supposed to be the science desk? 'eventually die from having too much of this inner filth' is at best 'a little simplistic' Nil Einne (talk) 22:47, 3 April 2011 (UTC)[reply]

An abundance of dietary fiber may help. ~A H 1^(TCU) 22:49, 3 April 2011 (UTC)[reply]

Actually there was an odd news story along this line that I just remember - C. elegans live longer if given just the right dose of thioflavin T, because it helps them clear out old misfolded proteins.^[1] Wnt (talk) 06:29, 4 April 2011 (UTC)[reply]

The good Dr. Kellogg was concerned for the cleanliness of his patients' intestines, every one of whom was plied with water, from above and below. His favorite device was an enema machine that could rapidly instill several gallons of water in a series of enemas. Every water enema was followed by a pint of yogurt — half was eaten, the other half was administered by enema, “thus planting the protective germs where they are most needed and may render most effective service." It is more practical to injest at one end yogurt with the doctor's famous cereal and let your washlet take care of the other. Cuddlyable3 (talk) 08:43, 4 April 2011 (UTC)[reply]

The build-up of internal toxins is the rationale for detox diets, but as that article says, most scientists reckon detox diets are worthless and there's no evidence that they remove accumulated toxins, or that the toxins exist. --Colapeninsula (talk) 13:40, 5 April 2011 (UTC)[reply]

about black holes

i had a doubt if the universe is formed by big bang and all the mass and energy containing in the universe at present must co me from that singularity. if it happens like that according to law of conservation of mass and energy they cannot be created nor destroyed but how they came in action? — Preceding unsigned comment added by Tin roy (talk • contribs) 08:28, 3 April 2011 (UTC)[reply]

According to our Big Bang article, this event started from a state that was extremely dense not that was "nothing". The whole idea of a singularity is a bit weird--it's definitely not a nothing. A valid question would be "Where did all that matter come from before the singularity exploded?" It is an active area of study and an unsettled aspect of theory related to the Big Bang. It's...somewhat complicated. DMacks (talk) 09:28, 3 April 2011 (UTC)[reply]

Conservation of mass-energy is a consequence of homogeneity in time as per Noether's theorem. But there wasn't a homogeneity in time at the big bang singularity, because that singularity is a boundary, so conservation of mass-energy is not required to hold at the singularity. Besides, who is to say that the total mass-energy of the universe isn't exactly zero? After all, even in Newtonian gravity, gravitational energy is negative, and in general relativity the concept of gravitational energy is a complicated mess that doesn't even have a universally agreed upon definition. Red Act (talk) 09:45, 3 April 2011 (UTC)[reply]

Good question unsigned."how they came in action" sentence construction needs a little adjustment, but you get right to the 'heart' of the whole 'big bang' question. To say that it all started with an infinitely small, infinitely hot "point, spot, area, anomally, entity" is about as explanatary/nonexplanatary as the old idea 'god done it'. Even though perseived motions of some galaxies seem, by logical exrapolation, to indicate a single point origin, there's no reason to suppose that that extrapolation is the only possibility. could be the logic was taken to far, just as it has been with numerous other accepted ideas.big bang is a popular idea which I think will eventually be debunked.Phalcor (talk) 15:20, 3 April 2011 (UTC)[reply]

The Big Bang doesn't have to be "debunked". The singularity never happened and nobody claims that it did. It is, as you say, the (formal) result of an extrapolation from the observed conditions in the universe backwards in time. However, before the extrapolation reaches the singularity, the conditions in the universe (e.g. temperature and pressure) become such that none of our current physical theories can be applied any more. The missing time from that point to the singularity is at least the Planck time, i.e. some 10⁻⁴⁴ seconds. While there are some speculative ideas, it is fair to say that nobody really knows what went on before that time. --Wrongfilter (talk) 17:39, 3 April 2011 (UTC)[reply]

There are many theories on what triggered this big bang, for example brane theory and a big crunch of some previous universe. ~A H 1^(TCU) 22:47, 3 April 2011 (UTC)[reply]

Moving a Space Shuttle

This URL is for an opinion piece about the future locations of the space shuttles. http://www.washingtonpost.com/opinions/shuttle_descent/2011/03/30/AFFsvHQC_story.html The piece says: "Moving, cleaning and preparing the shuttles for display will cost slightly more than $28 million apiece and require extensive precautions — the vessels are too fragile to travel in the rain and require two 747 jets to carry them". Is this true? How can a vehicle too fragile to be moved in rain survive the high vibration of takeoffs and the stresses of re-entry? When being moved by two 747's, are both the 747s lifting the shuttle or is the shuttle taken apart to be moved? Both these options seem unlikely. Thanks, Wanderer57 (talk) 16:08, 3 April 2011 (UTC)[reply]

Don't know about the storage plans, But Ive seen shuttle transportation on TV about a hundred years ago "it seems", and the shuttle rides piggyback on one 747. I read the article. Looks like journalistic error.Phalcor (talk) 16:30, 3 April 2011 (UTC)[reply]

One thought. the spokesman may have said something like, "We have two 747's available to move the shuttles". you could see how an uninformed journalist might miss-interpret that.Phalcor (talk) 16:51, 3 April 2011 (UTC)[reply]

Like this. I saw one fly over London once - maybe a hundred years ago ;-) Alansplodge (talk) 18:45, 3 April 2011 (UTC)[reply]

~~Let me guess: you woke up later with a hangover, yes?~~ Struck by poster with apologies to Alansplodge who is only 74 years off. Cuddlyable3 (talk) 08:56, 4 April 2011 (UTC)Yes thank you. Just like that. — Preceding unsigned comment added by Phalcor (talk • contribs) 20:22, 3 April 2011 (UTC)[reply]

Cuddlyable3 you interjected between. tricky but funnier. however I can't imagine what it was doing over London since according to my memory those shuttle transport flights took place only INTRAcontinental not 'inter'. However that is/was how they were moved.Phalcor (talk) 21:36, 3 April 2011 (UTC)[reply]

Here's an article about the Shuttle/747 visit to London. Nanonic (talk) 22:23, 3 April 2011 (UTC)[reply]

Oh, ye of little faith Phalcor ;-) Alansplodge (talk) 00:01, 5 April 2011 (UTC)[reply]

As for the reference to the rain, maybe they mean it can't travel ON the 747 in the rain? As in the combination of being on the plane AND in the rain is what it's too delicate for. Vespine (talk) 22:45, 3 April 2011 (UTC)[reply]

Space Shuttle Enterprise 747 separation APL (talk)

And just because no one has mentioned it yet, of course there's the climactic scene in Moonraker where the shuttle is hijacked and takes off FROM the top of the flying 747. As many websites point out however this would have been impossible, not least because the the fuel for the shuttle's main engines is not carried "on board" but comes from the big tank it is attached to during take off. Vespine (talk) 06:23, 4 April 2011 (UTC)[reply]

A forgivable error since the shuttle didn't actually launch until 1981. Googlemeister (talk) 13:56, 4 April 2011 (UTC)[reply]

Of course, they have actually launched it that way, but not to orbit. Just for landing tests. Enterprise made five flights that way. APL (talk) 19:26, 4 April 2011 (UTC)[reply]

I can't resist posting this Shuttle Carrier space comedy. --Sean 16:26, 4 April 2011 (UTC)[reply]

Steam train in a tunnel

I am old enough to remember that passengers on a steam train would have to close any windows if they went into a tunnel, to prevent their compartment filling with smoke. But how did the driver and fireman fare on the open footplate? I can't believe that smoke deflectors would have been effective in a tunnel, or that the smoke would somehow remain within the tight space above the engine until the cab had passed under it. Surely they couldn't simply close their eyes (and noses). Was the cab somehow designed to trap a pocket of air?--Shantavira|^{feed me} 17:28, 3 April 2011 (UTC)[reply]

Cab forward design of engines is one solution.--78.150.224.119 (talk) 21:23, 3 April 2011 (UTC)[reply]

Well, conceivably the health and comfort of mere employees were not taken as seriously in those days as that of paying passengers. At the least, drivers and firemen would expect their work clothes to become filthy with smoke and coal dust; there are also references to locomotive drivers wearing protective goggles to be found aound the web. –Henning Makholm (talk) 21:31, 3 April 2011 (UTC)[reply]

I remember actually traveling on steam locomotives and I recall virtually all the smoke being left behind the engine. The smoke,having very little mass, would immediately lose it's forward momentum to air resistance. So by the time the smoke swirled down to the level of the windows the engine would be already passed the smoke zone, The smoke being available only to the passengers.Phalcor (talk) 22:10, 3 April 2011 (UTC)[reply]

This page from the Brunel Museum about the Thames Tunnel says; "...trains running through the tunnel were hauled by steam engines. Entering the tunnel the trains would go downhill towards the low point in mid-river before starting the climb back up to the surface. The steam engines would have to work hard pulling the heavy freight trains back up to the surface. The harder a steam engine works the more smoke it produces. In railway tunnels on land there are frequent shafts to allow the smoke to escape to the surface. No ventilation shafts could be built in the river so The Thames Tunnel was full of smoke making life very unpleasant for the steam engine drivers and firemen." Alansplodge (talk) 00:07, 4 April 2011 (UTC)[reply]

Me again. This page says "The Combe Down Tunnel was built in 1874... The tunnel has no ventilation along its 1 mile length, at the time of construction it as the longest un-ventilated tunnel in the UK. The lack of ventilation, on occasions caused problems to slow moving trains. In one instance a train's driver was overcome by smoke, on exiting the tunnel the train crashed in to a goods yard, killing the driver and two railway employees in the yard". Alansplodge (talk) 00:16, 4 April 2011 (UTC)[reply]

I have read about steam locomotives carrying hooded contraptions for use by the crew when travelling through tunnels. These contraptions were made of canvas and worn over the head and shoulders. They had glass lenses to allow the wearer to see out. There was also mention about drawing air from below the footplate, so perhaps these contraptions had pipes that could be connected to some area where there would be little or no smoke. I have also read about the crew lying on the footplate to avoid the worst of the smoke when in a tunnel, so it was definitely a problem. Dolphin (t) 00:58, 4 April 2011 (UTC)[reply]

This heritage rail newsletter includes a piece about a journey in the cab of a Fell Engine on the Rimutaka Incline in the 50s, where four engines were hitched to the train: ...there was a short whistle blast from the lead locomotive. Norm produced a damp towel from somewhere and shouted "Here wrap this around your face and get down as low as you can". [...] Very shortly we entered the first tunnel. The fiery exhaust which had previously shot so spectacularly metres into the air was now hitting the tunnel roof just above the funnel and raining down onto the locomotive. In no time the cab was full of choking sulphurous smoke and the temperature was rocketing up. Soon any exposed skin began to sting - it was becoming distinctly unpleasant. Suddenly there was a rush of beautiful cold air. We were out of the tunnel and the engine's doors had been flung open, oh bliss! "The next bugger's worse" shouted Norm. [...] Too soon the dreaded whistled signal from the lead loco. I wrapped the towel around my head again and crouched back down on the coal pile - at least it was getting lower, I thought, I could get down lower this time.

Soon the familiar rush of air pressure as we entered the tunnel. Once again the sulphur and quick build up of temperature. This time however it continued - hotter and hotter it became. Now even covered skin began to sting. Hotter and hotter still, breathing became like swallowing fire. "Hold your breath" I thought, but soon another was necessary. But each new breath seared the lungs - scared to breathe, scared not too. Panic must have been very close. "Control yourself, this will soon end!" But hotter and hotter it became. I felt dizzy and reached out for support - even the loco's walls were hot. Now I know what hell is like. [...] Forty years later I can still clearly recall that searing heat and the sulphurous taste. Gwinva (talk) 02:24, 4 April 2011 (UTC)[reply]

Thanks everyone. Very interesting reading, but nostalgia is no longer what is used to be. And to think we all wanted to be engine drivers when we were kids...--Shantavira|^{feed me} 10:54, 4 April 2011 (UTC)[reply]

I wonder what happened if a train was ever obliged to stop with the engine in the middle of a tunnel, so long that the water cooled down. I would expect that running the engine (long enough there to get up enough steam to move the train) would kill the engine crew. Perhaps having a locomotive engine on each end would solve this, unless the tunnel was long enough for both ends to be inside. Plus, with an engine on each end, perhaps they could cut fuel to whichever end was in the tunnel (again assuming it's not longer than the train), and thus reduce the problem. Or maybe they could just get up enough speed to coast through the tunnel ? StuRat (talk) 19:24, 4 April 2011 (UTC)[reply]

This forum suggests that oxygen to get it burning would be a problem: even refers to some engines dying down, so mid and end engines were added (as per your speculation). The page also has some good pictures of drivers' hoods, smoke deflectors, and the tale of one man steaming the skin off his face during one difficult tunnel trip... Interesting suggestion that the smoke deflectors were to prevent damage to the tunnel roof by deflecting the blast, rather than any concern for the crew. Gwinva (talk) 00:10, 5 April 2011 (UTC)[reply]

types of motion

There are a few different types of motion but couldn't it just be one type of motion that creates all other. Couldn't all motion be one type of motion but in different forms —Preceding unsigned comment added by 82.38.96.241 (talk) 19:41, 3 April 2011 (UTC)[reply]

Here are two articles that may interest you. This one is about motion. It mentions a scientist named Albert Einstein but before you read more about him, this article about Newton's laws of motionwill help you. Cuddlyable3 (talk) 20:46, 3 April 2011 (UTC)[reply]

Yes I have read that article in English but my question was about types of motion and whether there was just one type of motion in different forms —Preceding unsigned comment added by 82.38.96.241 (talk) 21:33, 3 April 2011 (UTC)[reply]

Well, there's linear motion and rotation, if that's what you meant. One can be changed into the other, but then it's a matter of terminology whether you call them two different types of motion or two manifestations of one form of motion. Similar problems exist with mass versus energy and electricity versus magnetism. StuRat (talk) 22:06, 3 April 2011 (UTC)[reply]

There are different types of motion defined by vector properties. For example, see uniform motion, uniform acceleration, circular motion, gravitational acceleration, free fall, terminal velocity and jerk. ~A H 1^(TCU) 22:44, 3 April 2011 (UTC)[reply]

But all of these are just special cases of, well, motion. It's not an exhaustive classification of all possible motions. StuRat's example of linear motion and rotation is a bit better -- every smooth 3D motion is exactly one of these (or "nonmoving") at any point in time, but since one is a limiting case of the other, it's more a matter of how we analyse it than any deep difference.

I'm still struggling to find a sense of the question where the answer could be anything else than: Yes, of course all these kinds of motion are instances of a common underlying phenomenon, namely "motion". How could it conceivably be otherwise? Why do you even ask? –Henning Makholm (talk) 23:04, 3 April 2011 (UTC)[reply]

Er.uh.we didn't ask. you did.190.56.125.192 (talk) 23:18, 3 April 2011 (UTC)[reply]

I, too, am not sure I understand what's really being asked here, but perhaps Motion (physics) would be of use to you?

Motion should make more sense to you if you study a little bit of Newtonian mechanics, even at the elementary level that they would teach in a sixth form physics class.

There are different types of causes of motion, i.e., different types of force, and there is a decades-long effort underway to unify those forces, with some but not complete success. Is that perhaps what you're really asking about? Red Act (talk) 00:47, 4 April 2011 (UTC)[reply]

Motions are defined by the six degrees of freedom that a ship, boat or any untethered object can experience. It was long assumed that there is no difference between these motions until the Lorentz-Fitzgerald contraction hypothesis about speeds approaching the speed of light, which was later resolved by Einstein's theory of Special relativity. Cuddlyable3 (talk) 09:11, 4 April 2011 (UTC)[reply]

i was on about types of motion like linear and rotation and whether they are just one type of movement —Preceding unsigned comment added by 82.38.96.241 (talk) 15:59, 4 April 2011 (UTC)[reply]

pH of water containing dissolved substances and release rate of carbon dioxide

Hi. Where can I find publications about the correlation between the pH of either ocean water or water under experimental conditions and its effects on how quickly carbon dioxide and its dissolved carbonic acid counterpart can either be released into the surrounding air and how much dissolved gas the water can hold at a specific temperature? This is not a homework assignment. However I am considering researching and doing experiments using this idea on a non-curricular basis. Thanks. ~A H 1^(TCU) 23:35, 3 April 2011 (UTC)[reply]

[2] may not qualify as a reliable source, but I can confirm that the information in it regarding CO2 and pH seems, at a first approximation, accurate and informative, so I recommend reading what it has to say on the subject. There is a very helpful graph which shows the relationship between pH and the various components of the carbonic acid-hydrogen carbonate-carbonate equilibrium. Strictly speaking, so long as the pH is kept at a level where there isn't an appreciable amount of the H2CO3 form present, there will not be substantial outgassing of CO2. Once the pH reaches a level that the equilibrium shifts to the carbonic acid form, you should see that the relevent equilibrium is the CO2-H2CO3 equilibrium, as covered the first part of the document I gave. These calculations seem very much like ones a student may encounter in a second-semester chemistry course (usually "Quantitative Chemistry") where intensive equilibrium calculations occur. You should have the background to work out the figures on the solubility of H2CO3 at various pHs given the information in that document. Heck, I am pretty sure I have done the problem directly, either when teaching this material myself or when tutoring students taking said class. --Jayron32 04:14, 4 April 2011 (UTC)[reply]