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September 22

Cancer

I heard that they can take a sample of tissue that is cancerous (for example some breast tissue in breast cancer) and know how serious it is and how far it advanced. How is one piece of cancer tissue different than another? How can they tell its more serious than another? —Preceding unsigned comment added by 76.169.33.234 (talk) 01:38, 22 September 2010 (UTC)[reply]

There are a number of ways of ranking cancer severity, including staging. In addition to looking at metastasis and lymph node involvement, one can perhaps look for the level of cellular change to determine dysplasia, metaplasia, carcinoma-in-situ, etc. DRosenbach ^{(Talk | Contribs)} 03:48, 22 September 2010 (UTC)[reply]

Cancerous cells can look like normal cells, only growing out of control, or they could have say, their lung cell genes kind of too mutated that they look disorganised. John Riemann Soong (talk) 16:48, 26 September 2010 (UTC)[reply]

house foundation

how to repair house foundation from water damage? its slanted —Preceding unsigned comment added by Kj650 (talk • contribs) 04:20, 22 September 2010 (UTC)[reply]

There's no solution to that that doesn't cost a hell of a lot of money, so you better get professional advice. Looie496 (talk) 05:04, 22 September 2010 (UTC)[reply]

You need a house jack. You also need someone who knows how to operate it. You also need someone who can rebuild the foundation once your house is jacked up, and then replace the house upon it. All very expensive. This is not something you can do yourself, unless you happen to be the sort of person who owns a foundation repair company. --Jayron32 05:09, 22 September 2010 (UTC)[reply]

I doubt we can give you advice, but for sure we can't give you advice without a photo. Ariel. (talk) 08:27, 22 September 2010 (UTC)[reply]

Iodized salt

I saw that the low-sodium iodized salt supermarkets sell contain sodium chloride, potassium chloride and potassium iodide. I know that sodium chloride and iodine is important for the human body, but is potassium chloride and iodide (the compound itself) beneficial, or required by the body in any way? YOSF0113 (talk - contributions) 06:12, 22 September 2010 (UTC)[reply]

Yes. Once dissolved, potassium chloride breaks into its respective ions, potassium and chlorine. Potassium has many important biochemical functions, most notably its role in the "sodium-potassium pump". Nimur (talk) 06:48, 22 September 2010 (UTC)[reply]

The beneficial effect of potassium chloride in low-sodium table salt is that it isn't sodium chloride. Our article on low sodium diet describes why it is beneficial for some groups of people to limit their intake of sodium ions, and one simple way to do this is by using low sodium salt instead of normal table salt (although it's unlikely to be sufficient on its own without other changes in diet). Potassium iodide is added as a source of iodine; potassium iodate can be used as well: either compound can be used by the thyroid gland. You could use sodium iodide for this purpose, but potassium iodide is cheaper (about 40% cheaper for kilogram quantities, probably even more so for bulk quantities). Physchim62 (talk) 11:23, 22 September 2010 (UTC)[reply]

Potassium is absolutely critical for life, but the body doesn't eliminate it very rapidly, so the great majority of people get enough in their diets without having to do anything special. See hypokalemia (i.e., "low potassium") for the few exceptions. Looie496 (talk) 17:15, 22 September 2010 (UTC)[reply]

I wonder if those people should avoid adding salt to their diet instead. Imagine Reason (talk) 00:30, 24 September 2010 (UTC)[reply]

transmission

where the multiple circuit lines used.. —Preceding unsigned comment added by Chanuu.. (talk • contribs) 06:31, 22 September 2010 (UTC)[reply]

Would you clarify your question? "Multiple lines" sounds like parallel communication, but beyond that I can't tell what you're looking for. — Lomn 13:55, 22 September 2010 (UTC)[reply]

The question might also apply to an electrical power system, where parallel lines are used to maintain continuity of service when one line trips and avoid overloads when heavy currents are carried between buses. Within a single phase on a single line on a single transmission tower, multiple parallel bundled conductors, spaced a short distance apart apart, are used to keep the impedance lower and to reduce radio interference [1]. Edison (talk) 19:10, 22 September 2010 (UTC)[reply]

is sulfamethoxazole is short acting or intermediate acting sulfonamide

Respected sir, you are mentioned "sulfamethoxazole" as short acting sulfonamide but in the book of pharmacology by "kd tripathi" sulfamethoxazole is mentioned as intermediate acting sulfonamide.could you please explain about it —Preceding unsigned comment added by 117.199.244.167 (talk) 09:48, 22 September 2010 (UTC) Question reformatted to return within window. Caesar's Daddy (talk) 10:01, 22 September 2010 (UTC)[reply]

Actually, our article classifies it as an intermediate-acting sulfonamide, so there is no conflict with your reference. This seems fairly evidently true by it's half life of 10 hours. Regards, --—Cyclonenim | Chat 14:20, 22 September 2010 (UTC)[reply]

Can giraffes cough?

My work's intranet home screen includes a random "fact" and I just saw one that I don't quite believe: Giraffes don't cough. I googled it and got the answers- yes they can and no they don't. So this is bugging me. The Wikipedia article says that the males make a coughing noise, but is that an actual cough as in, clear your throat/cough up your lungs type cough? Do they actually cough or just make cough-like noises? MorganaFiolett (talk) 12:07, 22 September 2010 (UTC)[reply]

I've looked around and can't find a specific reference, but I don't see any reason to believe they wouldn't cough. They have similar features in that region as we do, just somewhat elongated. They still have a long trachea, and I can't find a reference to say they don't possess the C fibers needed to initiate the cough. Furthermore, if we humans have to cough regularly to effectively clear out comparatively short airways, I'd imagine they have an even greater need to do so. Regards, --—Cyclonenim | Chat 14:15, 22 September 2010 (UTC)[reply]

Good question. Our article on Cough is absolutely terrible for non-humans. Our giraffe article claims that "Courting males will emit loud coughs", but that claim isn't sourced. --M @r ē ino 14:24, 22 September 2010 (UTC)[reply]

Google scholar coughed up the snippet "Cough is not a feature of the giraffe's behaviour possibly because of the high protective aryepiglottic folds and herbivorous diet." [2] (D. F. N. Harrison, "Biomechanics of the Giraffe Larynx and Trachea", Acta Oto-Laryngologica 1980, Vol. 89, No. 3-6 , Pages 258-264 [3]). Unfortunately I can't view the study. ---Sluzzelin talk 16:29, 22 September 2010 (UTC)[reply]

Just curious, but why would a herbivorous diet affect the frequency of coughing? Fair play on the aryepiglottic folds thing, though. Regards, --—Cyclonenim | Chat 17:26, 22 September 2010 (UTC)[reply]

I guess because they chew cud. (Not all herbivores chew cud, of course, but giraffes do). Many captive ungulates die when cud gets into the wrong pipe, say, after anesthesia. --Dr Dima (talk) 18:28, 22 September 2010 (UTC)[reply]

I didn't understand your last point, Dima -- humans can die if they aspirate regurgitated food after anesthesia, so what does that have to do with ungulates, ruminants or giraffes? DRosenbach ^{(Talk | Contribs)} 20:19, 22 September 2010 (UTC)[reply]

... and cud-chewers and other herbivores do cough, though perhaps not in quite the same way as humans? Dbfirs 05:59, 23 September 2010 (UTC)[reply]

Fleischmann–Pons experiment

Yesterday in the course of a public lecture on financial engineering, the speaker mentioned in passing that the Fleischmann–Pons effect, widely considered discredited, was actually valid, and the attempts to reproduce it failed because they weren't done right. That's all he said about that. I haven't heard any updates since the time this was first in the news. Was there something more recent that I missed? Michael Hardy (talk) 16:53, 22 September 2010 (UTC)[reply]

There are plenty of claims, but not very many that are taken serious. If you have the stomach for it, talk:Cold fusion has been a battleground for the last year or so, and you can probably find all the claims and counterclaims there. Basically, something interesting may be going on, but it's almost certainly not fusion, and almost certainly not a real source of usable energy. The slope from reasonable to fringe to total cook is fairly steep and quite slippery in that field. --Stephan Schulz (talk) 17:06, 22 September 2010 (UTC)[reply]

Diastolic Dysfunction

Our article on the above topic says:

Some causes of left ventricular stiffening include:

* high blood pressure (i.e. hypertension, where, as a result of left ventricular muscle hypertrophy to deal with the high pressure, the left ventricle has become stiff)

* aortic stenosis of any cause (here as with hypertension, the ventricular muscle has hypertrophied and thence become stiff, as a result of the increased pressure load placed on it by the stenosis)

*scarred heart muscle (e.g. occurring after a heart attack) (scars are relatively stiff)

* diabetes (stiffening occurs presumably as a result of glycosylation of heart muscle)

* severe systolic dysfunction that has led to ventricular dilation (i.e when the ventricle has been stretched to a certain point, any further attempt to stretch it more, as by blood trying to enter it from the left atrium, meets with increased resistance - it has become stiff

* reversible stiffening as can occur during periods of cardiac ischemia

Does anyone know of other causes, or is this "Some" weasel wording? If there are other known causes, could the responder elucidate? Thanks Bielle (talk) 18:02, 22 September 2010 (UTC)[reply]

Without comment on the specifics...

I don't see "some" here as an instance of weasel words, provided the list isn't in dispute. Sources would certainly help, but it's no more weasel-ey than "some major US cities are NYC, Chicago, and LA". Contrast with "some say that Chicago is better than NYC", where "some" props up a questionable claim.
All that said, if "some" is a matter of concern, go ahead and remove it. "Causes of left ventricular stiffening include:" is also a perfectly good list introduction, and (perhaps unlike this answer) avoids unnecessary words. — Lomn 18:16, 22 September 2010 (UTC)[reply]

I think death causes that too, OP, if you are trying to assemble a complete list. ;) WikiDao ☯ (talk) 19:22, 22 September 2010 (UTC)[reply]

What I am really asking is whether or not there are other known causes, death aside. The use of "some" suggests that there are. And, if there are others, could someone tell me about them? Thanks. Bielle (talk) 21:18, 22 September 2010 (UTC)[reply]

One additional cause would be hypertrophic cardiomyopathy. Although not discussed in depth in our article, diastolic dysfunction can be seen in genetic forms of cardiomyopathy (see [4] for example). --- Medical geneticist (talk) 21:38, 22 September 2010 (UTC)[reply]

There's heaps of things that cause diastolic dysfunction and the article list is by no means exhaustive. Death actually isn't one of them, since death produces an absence diastole and systole, and the definition of diastolic dysfunction requires that diastole is happening. But if you want to think about this in broader terms, you can make a big list of anything that impairs myocardial compliance under headings of precardiac, intracardiac and postcardiac. Precardiac causes are the least common, and all I can really think of would be things that prevent venous return to the heart, such as haemorrhage, peripheral vasodilation or inferior vena caval obstruction. Intracardiac causes include mitral valve and aortic valve diseases (prolapse and stenosis), the cardiomyopathies (dilated and hypertrophic), myocardial lesions (infarction, tumour eg rhabdomyosarcoma, myxoma, deposition diseases like amyloidosis, sarcoidosis, for example). The major post cardiac cause is atherosclerosis (or peripheral vascular disease) and hypertension. Type 2 Diabetes is a major cause of atherosclerosis and hypertension, and this is probably the most significant contribution diabetes has to diastolic dysfunction. Further to these pathophysiological causes, there's also exogenous causes, particularly drugs - prescribed and non-prescribed (chronic cocaine use can produce spectacular myocardial hypertrophy, but this is also true of anything that is used long term that increases the rate or force of heart muscle contraction). This isn't an exhaustive list either! Cheers, Mattopaedia ^{Say G'Day!} 07:20, 23 September 2010 (UTC)[reply]

My speculation about "death" was as a "cause" of "left ventricular stiffening". I concede that "not functioning at all" is a stretch of what is meant by "dysfunction." But would not death cause "stiffening" in the associated smooth muscle, at least for a few hours? WikiDao ☯ (talk) 20:21, 23 September 2010 (UTC)[reply]

Thank you all! Bielle (talk) 02:33, 26 September 2010 (UTC)[reply]

Why does it take so long to get toxicology results?

Our article Forensic toxicology describes various tests used to see what drugs, poisons, or other substances were present in the body of a person who died under questionable circumstances, but does not address the long time frame. News stories typically say the toxicology reports take "up to two months." On TV crime shows, (granted, they are not reality) they put a tiny sample of blood or tissue in a Mass spectrometer and the peaks in the graph indicate the elements and compounds present. I have had samples of industrial substances analyzed by mass spec and gotten results in less than a day. Chromatography in various forms is another tool. I do not understand why either test would consume 8 weeks, or perhaps 6 weeks allowing for shipping and report writing. Are the samples from one individual really undergoing analysis on a daily basis for a month or two, or do they wait in queue then get a few days' analysis? Blood alcohol can be measured pretty quickly. My hospital's lab can do a wide range of tests on blood or urine overnight. Are there chemical reactions which take weeks to arrive at a result, which the delivery of quicker tox results must await? Edison (talk) 18:25, 22 September 2010 (UTC)[reply]

How many people are doing tox screens and how many tox screens do they have to do? Googlemeister (talk) 19:32, 22 September 2010 (UTC)[reply]

Probably not a reason, actually. The Tox people have a limited sample, and they can't do all the possible tests on it: simple things (like blood alcohol) can be done quickly, but anything complicated might have to wait for a standard to be delivered. Physchim62 (talk) 19:40, 22 September 2010 (UTC)[reply]

Do you think there is any particular test which resides in a GCMS. some fancy analyzer or even a test tube for more than a week? Is the rest just a queue/backlog delay and a delay for retest to confirm the presence and concentration of substances of forensic interest? If it were of paramount national interest, and prompt results were demanded, would the 8 weeks turn into 24 or 48 hours? Edison (talk) 04:35, 23 September 2010 (UTC)[reply]

There are at least some examples of tests that really do take weeks of lab time. The most obvious are ones based on forming bacterial cultures to detect pathogen types, which for some strains of pathogens can be very slow / difficult due to the bug's reluctance to grow in vitro. (Though in recent years, molecular and DNA tests have reduced the need for culturing in many cases.) Dragons flight (talk) 06:11, 23 September 2010 (UTC)[reply]

In autopsy specimens, a rather large standard battery of drugs and other substances is usually tested for, and this includes a range of opioids and benzodiazepines, alcohol and other illicit substances like ephedrine derivatives (speed, ecstasy, ice, etc), cocaine, cannabinoids, as well as a large range of prescription drugs like paracetamol ( aka acetominaphen), salicylates, diuretics, antihypertensives and other drugs that effect heart function, antidepressants and antipsychotics. Usually this is performed on one or two tubes of blood, which needs to be shared out for all those different GCMS runs, which are all batched together so sample from a number of autopsy cases are analysed together. This all takes a fair bit of time. Then the results need to be reviewed and validated by an experienced toxicologist, and those results are then interpreted in the context of the autopsy findings by the forensic pathologist before the report is prepared for the coroner. If some of the results are dubious and restesting is required, the process can take months. Usually when its a famous person, this process is fast-tracked, and it still takes a few weeks. Mattopaedia ^{Say G'Day!} 07:42, 23 September 2010 (UTC)[reply]

Another possibility may simply be logistical. Most local police agencies (except in larger cities) do not have their own criminologists, and even those which do lack some of the more sophisticated equipment, usually for cost reasons. For them, they must ship the material to be tested to a larger agency (in the U.S., typically the state police or a large nearby city), where it must wait in the queue along with all of the tests that agency is doing for itself. — Michael J 14:48, 25 September 2010 (UTC)[reply]

What places endangered by global warming would make good vacation choices?

What if I decided to spend my next vacation somewhere that has a good chance of being underwater, uninhabited, or radically changed by global warming in my lifetime? Is the environment changing so fast that it's plausible that I could tell my grandchildren that I visited (place x) while it was still above the waves? Or no? What places would make good choices for such a trip? (I'm planning to live about 50 years longer.) -FisherQueen (talk · contribs) 22:07, 22 September 2010 (UTC)[reply]

Visit the Maldives. At only 8 feet (max) above sea level, they will be the first to disappear if sea levels rise. Dbfirs 22:34, 22 September 2010 (UTC)[reply]

One travel blog also suggests ~~Chacaltaya~~ (too late, the glacier's gone), the Greenland ice sheet, Bangladesh, the Himalayas, Kiribati, the Great Barrier Reef.[5]. I'd throw in skiing holidays in some of the lower Alpine regions or at Snoqualmie. ---Sluzzelin talk 23:30, 22 September 2010 (UTC)[reply]

The North Pole will look a lot different. Your grandchildren will know that Santa Claus had to move from the North Pole to the South Pole because of global warming. Count Iblis (talk) 00:45, 23 September 2010 (UTC)[reply]

Well it would have to rise by about 10m before inundating the National Mall, but that's a nice place to visit (and knowing the way they are down there, I'm sure they'll just put up some concrete barricades or something lol;). You can see a map of what various sea-level changes would do to anyplace in the world on the Global Sea Level Rise Map. Our Current sea level rise article expects there to be a maximum rise of 2m over the next century, but most likely less than half that. WikiDao ☯ (talk) 04:41, 23 September 2010 (UTC)[reply]

Go check out the polar bears before they go extinct. Just don't try to feed them... Matt Deres (talk) 13:12, 23 September 2010 (UTC)[reply]

Venice is an obvious answer, but New Orleans may be a good choice as well. As the ocean level rises it will become more and more vulnerable to hurricanes.

Have you considered checking out animals the may soon go extinct?

Or be in Florida to watch the final Space Shuttle launch. Tell the grandkids that you can remember when USA had a man-in-space program. APL (talk) 16:34, 23 September 2010 (UTC)[reply]

Sea level rise is unlikely to be more than 1m in 50 years, and likely less than that. For radical change a melting glacier is a pretty good choice; there are lots of those (retreat of glaciers since 1850) William M. Connolley (talk) 17:28, 23 September 2010 (UTC)[reply]

I'd visit the future former Glacier National Park (U.S.). -Atmoz (talk) 17:56, 23 September 2010 (UTC)[reply]

Some scientist are beginning to think -and find archaeological evidence for- major climate shifts that can happen abruptly. So... Would it not impress your grandchildren more if you just stayed where you are? When the climate flips, you can recount to them: Oh yes! I can remember when there were herds of people, roaming across these plains as far as the eye could see. There were millions of them, all driving around in auto-mobiles. They slept in very tall air-conditioned buildings which were lit by electricity. They burnt millions of gallons of kerosene each day just so they could fly to far off places in aluminium cans -all for the fun of it. Then you can explain to them what a motor car was and were electricity used to come from and why they have no friends to play with etc. Of course, you run then run the risk of them suspecting that granny is prone to exaggerate more than just a little bit. Six horses pulling a cart perhaps, but carts with 250 of them hidden under a hood...?--Aspro (talk) 19:17, 23 September 2010 (UTC)[reply]

"I remember when petroleum was cheap enough to burn."

Along those lines, some people predict that fast world travel will become prohibitively expensive in our lifetimes. If that turns out to be true, just visiting distant lands would be enough. APL (talk) 22:10, 23 September 2010 (UTC)[reply]

Ha! Really think that would happen? Well it could. I don't think the environment is changing fast enough in any place, unless there is a tsunami on one of those islands... then the environment will change rapidly. :) --Chemicalinterest (talk) 11:11, 26 September 2010 (UTC)[reply]

Kiribati is worth a look. HiLo48 (talk) 03:26, 27 September 2010 (UTC)[reply]

substitution for lye water in a recipe

I'm trying to make homemade mooncakes and the recipe calls for 1 tsp lye water.....what disturbs me is that I have no idea what the concentration of such lye water would be. Is that 1 teaspoon 1M NaOH?

Most importantly, I don't really want to use lab-grade sodium hydroxide in my food.... is it possible to substitute with food-grade potassium carbonate solution? It's getting added to filling. John Riemann Soong (talk) 22:25, 22 September 2010 (UTC)[reply]

In On Food and Cooking it says that lye water is used in the manufacturing of pretzels as a 1% solution to help create the hard crust, but that sodium carbonate can be used instead. It must be being used only because it is alkaline so I'd guess that KCO3 would also be ok. Somebody here says you can find lye water in Chinese grocery stores, so that might be your best option. Smartse (talk) 23:18, 22 September 2010 (UTC)[reply]

Is that 1% by weight or molarity? John Riemann Soong (talk) 00:23, 23 September 2010 (UTC)[reply]

A percentage concentration almost always implies by weight per volume (w/v), see also percentage solution; molarity is never expressed as a percentage. TenOfAllTrades(talk) 01:28, 23 September 2010 (UTC)[reply]

Sometimes I see things like "5% acidity" in vinegar. John Riemann Soong (talk) 02:31, 23 September 2010 (UTC)[reply]

That means 5% (w/v) acetic acid. TenOfAllTrades(talk) 03:07, 23 September 2010 (UTC)[reply]

There is, however, such a thing as molar percent. -- 174.24.192.84 (talk) 05:13, 23 September 2010 (UTC)[reply]

Sodium carbonate can be made easily by heating a small amount of sodium bicarbonate in a pan. --Chemicalinterest (talk) 11:11, 23 September 2010 (UTC)[reply]

Solution? You can't seem to mean the powder. What replaces the proton? :S John Riemann Soong (talk) 14:12, 23 September 2010 (UTC)[reply]

Oh silly me, I think I see the reaction now. Another Na+ and the evolution of CO2. Pesky bidirectional multiple quilibria bicarbonates. Always throws me off in exams. John Riemann Soong (talk) 14:14, 23 September 2010 (UTC)[reply]

2 NaHCO₃ → Na₂CO₃ + CO₂ + H₂O --Chemicalinterest (talk) 11:12, 26 September 2010 (UTC)[reply]

Acid-base disproportionations are kind of interesting, where the same compound acts like an acid and a base. Note that the same really can't apply to water, at least not as a favourable reaction. Of course, maybe if water complexes gave off a gas when they combined... John Riemann Soong (talk) 17:30, 26 September 2010 (UTC)[reply]

Question about Einstein elevator and sensation of weight?

Suppose we have an elevator with a person stands on it's floor at ground level.

A- Let the whole unit starts accelerating upward exactly with 2g. It's net upward acceleration is g as the other g is canceling out the downward g.

B- Now after sometime, let the whole unit is stopped and dropped [may be upside down] with natural g from an appropriate height.

To me Weightlessness of an object [Zero gravity] is only possible if placed at the center and equidistance from the gravitating masses [equilibrium of forces] OR accelerating exactly at the same rate g of the gravitating mass but in opposite direction and in all other cases itt is under the influence of g or gravity force. Therefore I surmise that a person inside an elevator will not feel any sensation of his weight. I may be wrong but still doubt therefore I have the following

Questions:

So would the inside person in both flights feels his sensation of weight like stand on ground?

What direction would a person feels his sensation of weight force [equivalence principle] in Einstein elevator which accelerate exactly at same rate of g = 9.8 m/ s/ s in space?74.198.148.73 (talk) 23:48, 22 September 2010 (UTC) khattak#1[reply]

Edit: A- Let the whole unit starts accelerating upward with net earth gravity g at all times and behaves like Einstein elevator used for equivalence principle in space. Thus earth gravity g is cancel out at each point while accelerating upwards i.e. [2g upward - 1g downward = Net 1 g upward.]. The person is either hanging from the ceiling of elevator or from outside floor.

Thus to me, the condition of a person in both flight [accelarating upward and downward|] is same. —Preceding unsigned comment added by 74.198.148.78 (talk) 08:57, 23 September 2010 (UTC)[reply]

A - if the whole unit is accelerating upward at 2g, it is accelerating upward at 19.6 m.s^-2. Your suggestion about a net upward acceleration of one g is not correct. Dolphin (t) 23:57, 22 September 2010 (UTC)[reply]

(ec)You are confusing acceleration and force. If the elevator is accelerating up with 2g and with respect to a gravity field of 1g, it's accelerating with 2g (duh ;-), and anyone inside will feel 3g (2 from the acceleration, one from gravity). If the elevator is in free fall (i.e. "accelerating downward with g"), a person inside the elevator will not feel any gravitational force (until they hit the ground, of course). --Stephan Schulz (talk) 00:00, 23 September 2010 (UTC)[reply]

The experience of weightlessness doesn't imply the absence of gravity, but the absence of forces other than gravity. In other words if you were allowed to fall freely with gravity you would feel weightless (see for example Vomit Comet). If you stand on the ground, the ground acts on your feet with an upward normal force which is counteracting gravity and this is the weight you feel. In the elevator accelerating upwards, the upward force counteracting gravity is even stronger, and so you feel additional weight. Rckrone (talk) 00:13, 23 September 2010 (UTC)[reply]

When we are standing on the ground we don't accelerate downwards at 9.8 m.s^-2 because of the ground reaction force. When the ground reaction force acting on us falls to zero we say we feel weightless, not because our weight is zero but because the ground reaction force is zero. For example, when we dive or jump off a diving board our ground reaction force is zero and we feel weightless. Similarly, an astronaut in orbit or in the Vomit comet feels weightless because there is no ground reaction force. Dolphin (t) 00:18, 23 September 2010 (UTC)[reply]

... and, to answer your last question, - yes, an "elevator" or a spaceship accelerating at 9.8 m/s/s in free space (outside the obvious influence of any other mass) would appear to its residents to have "normal gravity" in the direction opposite to the acceleration. If they never looked out, they might believe that they were stationary on Earth. Dbfirs 05:53, 23 September 2010 (UTC)[reply]