Wikipedia:Reference desk/Archives/Science/2011 April 13

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April 13

Speed of Earth's orbit around the sun

I read that earth orbit's the sun at a speed of 107,000 KM/H, which seems mighty fast. Given this imense speed, I find it somewhat surprising that we do not feel any wind resistance here on earth. I mean if you stuck your head out of a car window travelling at 100 KM/H you would feel a strong gust of wind in your face, yet we are tearing through space at 107,000 KM/H without so much as a feint breeze? Perhaps somebody might be able to enlighten me as to why this is! Kind Regards. Paul —Preceding unsigned comment added by 79.71.91.21 (talk) 02:09, 13 April 2011 (UTC)

If you keep your head inside that car window, and keep the window closed, you also don't feel any breeze, yet you're still travelling at 100km/h relative to the road surface, because the air in the car is also travelling with you at 100km/h. Same with the Earth. Its air comes with us as we hurtle along, so we don't feel a thing. — Preceding unsigned comment added by HiLo48 (talk • contribs) 02:22, 13 April 2011

Yes, the speed of the Earth relative to the sun is very fast, but the sun is a very long way off. The sun is at such a great distance that even though the relative speed is 107 km.hr^-1 it takes the Earth one whole year to complete one trip around the sun. That is an angular speed of only 0.0411 degrees per hour which is extremely slow. There is no atmosphere between Earth and the sun, and no atmosphere means no wind when moving relative to the sun.

Earth's linear speed relative to the other planets in our solar system is also extremely large, but the angular speed is extremely small so we experience no effects from our speed relative to those planets.

A jet airliner might pass overhead at a speed of 1000 km.hr^-1 and a height of 40,000 feet (12 200 m) but you experience no effects because of the great distance between you and the airliner. If the jet airliner passed near you (close to ground level) you would experience many effects! Dolphin (t) 06:48, 13 April 2011 (UTC)

Paul you may be interested in the Michelson–Morley experiment that was carried out in an attempt to detect some kind of "wind" due to the Earth's motion, and is famous for having completely failed. (I simplified this story). Cuddlyable3 (talk) 13:52, 13 April 2011 (UTC)

Those experiments strongly (and unexpectedly) demonstrated a phenomenon that the then-current theories were totally unable to explain. For a physical experiment, that counts as a spectacular success -- the opposite of a complete failure. –Henning Makholm (talk) 16:14, 13 April 2011 (UTC)

Once again proving that there are no failures in science; a negative result is still a result, and it is all data. --Jayron32 18:56, 13 April 2011 (UTC)

Well, you can have failures, like when an experiment results in a vague result that's of no use at all, or when different people doing the experiment get different results. These usually mean the experiment was poorly designed. StuRat (talk) 06:33, 14 April 2011 (UTC)

No Henning Makholm. Lorentz-Fitzgerald length contraction was a theory that explained the negative result of the MM experiment. If Albert had not come along later with his special relativity we would probably still find Lorentz's aethereal hypotheses plausible. Cuddlyable3 (talk) 21:31, 13 April 2011 (UTC)

I would like to point out that the diameter of the Earth is 12,750 km, so the planet takes seven minutes to travel its own width. Meanwhile, your car travels its own width in a tenth of a second and a turtle walks its own width in maybe five seconds. If you were watching the Earth from above, it would look very slow. —Preceding unsigned comment added by 205.193.96.10 (talk) 16:03, 13 April 2011 (UTC)

Using decay heat in a nuclear reactor to spin a turbine

I did a presentation in a class of mine, and part of it discussed nuclear energy. The professor asked me if it was possible to use the decay heat produced in a nuclear reactor in a scram situation to spin a turbine which would power a water pump to cool the reactor. I was fairly certain that this idea was not possible simply because it does not generate enough steam to spin a turbine, but I'm not entirely sure. I'm pretty sure they disconnect the reactor from the turbine anyway during a scram for safety reasons. Can anyone confirm my guesses? ScienceApe (talk) 02:33, 13 April 2011 (UTC)

In principle the waste heat could be used to turn a turbine, though probably not the main turbine(s) used for regular electrical generation (the initial decay heat will be less than 10% of the reactor's regular output, and this will decline in the days following the scram). In practice, adding a second turbine (with all of the associated mechanical complexity and necessary preventive maintenance on parts that would be in working contact with radioactive coolant) isn't worth the complexity and cost over other solutions to drive the pumps. (Generally, grid power as the first option, and backup diesel generators as the second.) TenOfAllTrades(talk) 03:27, 13 April 2011 (UTC)

Wasn't that a system in place at Chernobyl that they were testing when the accident occurred? And I thought they referred to s similar system at the Fukushima 1 plants. A scrammed reactor should produce plenty of steam for a while to ruin emergency cooling pumps. Nuke plants are all about complexity and cost, with backups to backups. Edison (talk) 16:14, 13 April 2011 (UTC)

Did you mean to say "run" instead of "ruin" ? StuRat (talk) 06:27, 14 April 2011 (UTC)

The system being tested at Chernobyl was to run the cooling pumps off the residual kinetic energy of the turbine for the 60 seconds it would take to activate the emergency generators. --Carnildo (talk) 00:17, 14 April 2011 (UTC)

This system exists already, at least on french nuclear reactors (PWR). I think it exists also in the US since french reactors were originally constructed with a Westinghouse licence. This kind of steam turbine was also in place in Fukushima I nuclear reactors but you still need a cooling function to remove heat from the system if you want to operate with a closed cycle. You also need a minimum electrical supply to control it (this can be supplied with batteries). — Preceding unsigned comment added by Franssoua (talk • contribs) 12:49, 14 April 2011 (UTC)

whey gel

what exactly is whey gel? —Preceding unsigned comment added by 80.1.216.243 (talk) 03:39, 13 April 2011 (UTC)

It is a gel formed from Whey protein. You can read both of those articles to learn both what a "gel" is and what "Whey protein" is. --Jayron32 04:03, 13 April 2011 (UTC)

Universe = black hole, for some of time... or wait, only in the sideways version of time, which is length (*confused mumbling*)

OK I've been doing some thinking about the universe. Let's say there's this guy, and he's just chilling looking at our universe from the outside right before the big bang. Now, because the universe is ridiculously massive and small, it will appear to him like a black hole. And he is sitting right outside the event horizon (naturally this is the mother of all black holes - being the mass of the universe at ~1.6×10^55 kg and a Schwarzschild radius of approximately a two trillion light years [1] [2] - can this be right?!).

Now do I understand properly, that because he is outside the event horizon, everything that occurs within will be unobservable to him? Time on the surface of the event horizon is frozen for him, and time inside is on an entirely different plane of existence (piece of trivia: I heard one theoretical physicist put it this way: time bends on the fourth dimensional level, and length becomes time, and time length). As such, the big bang will never exist for our friend on the outside of the black hole. At best, current theories indicate he might (or might not) be able to deduce what occurs inside only from an extremely accurate reading of the Hawking radiation (see Holographic principle#Black hole information paradox).

Thus, if I understand properly, it is entirely possible that we live in a universe which is encapsulated within another universe, but the second universe will remain forever unattainable to us. No matter how much the universe expands, because we are dealing with infinitely small meters and units of time (on the event horizon, from the perspective of the outside... god knows what the hell happens inside), we will never reach that universe. I realize this isn't an entirely new concept (I saw Leonard Susskind explain it similarly), but it... kind of made sense to me for the first time tonight, when I thought it up on my own.

So I have some questions about all this:

1. If something were to enter the black hole from the outside, when and how would we perceive it on the inside?
2. Could it be, with the super-screwed-up-ness of time and space, that tracing back to the big bang is really just tracing back to the beginning of the existence of the black hole? And we would experience it entirely backwards (instead of matter falling in, vice versa), in a mad confusing turn of events because time is all goofed up.
3. Addendum to above: possibly all matter that can fall in has already fallen into the black hole before the big bang? And the entire external universe has already all ended, because it took infinite time for even a second to pass within? I'd have to assume Hawking radiation turned out incorrect. Thus we experience the big bang as the beginning of time, but really it's the end of time for the external universe. Much in the same way as someone traveling on a photon would have the entirety of time pass before experiencing even a second.
4. My understanding is that, given the right conditions of a spinning black hole, the singularity can be exposed to the outside world. What would happen then? What would it look like?

OK, I hope I haven't textwalled here too much, and I've stated this clearly enough that you all can understand it. I know I haven't stated it clearly. Anyway, am I making any sense at all?Magog the Ogre (talk) 06:37, 13 April 2011 (UTC)

Unlike some of the people here, I'm no expert, but aren't there a couple of problems with treating the big bang as a black-hole style singularity. I believe time and space came about in the big bang, standing outside it makes no sense. (unlike standing outside a black hole, of course) Isn't the concept of observing anything flawed with no concept of time and space? Grandiose (me, talk, contribs) 08:18, 13 April 2011 (UTC)

I have two questions:

1) can black hole return to expand or exploding to produce new objects?

2) about the big bang and expanding of universe ,there is no boundary and centre for universe , is there remnant matter in first point which big bang started?(this helps imagining )-78.38.28.3 (talk) 08:37, 13 April 2011 (UTC)

[Fixed your formatting for clarity, 78] In brief:

1) It is thought that, given long enough, all black holes will eventually evaporate by giving off Hawking radiation, but the time this takes is in some inverse proportion to their size, so black holes of star-mass or larger might take longer than the Universe itself will exist to evaporate (from the first link: "For a black hole of one solar mass . . . we get an evaporation time of 2.098 × 10⁶⁷ years"). Otherwise (we think), no.

2) There is no one "first point where the Big Bang started" because that point itself has now expanded to form the whole of the Universe. The Big Bang was also an expansion of space (and time) itself, not just of some matter within pre-existing space. To put it another way, everywhere is that "first point". This is, of course, very difficult for us to visualise. {The poster formerly known as 87.81.230.195} 90.197.66.111 (talk) 12:53, 13 April 2011 (UTC)

The error in your hypothetical scenario is subtle—it presumes that there is somewhere for an observer to sit outside the Universe, where he can watch the show. (That scamp Douglas Adams can be blamed for this perception, as he offered us the Big Bang Burger Bar as the natural complement to Milliways, The Restaurant at the End of the Universe.) Outside the Big Bang singularity, there just isn't any space to be in, and no way to watch the big...bang as it happens. TenOfAllTrades(talk) 15:10, 13 April 2011 (UTC)

4 It look like black hole from outside —Preceding unsigned comment added by 77.127.207.138 (talk) 15:47, 13 April 2011 (UTC)

Outside ? It's confusing to think about these things because of the tendency to think of the metric expansion of space being like a 2-sphere expanding into 3D space....but it isn't. Sean.hoyland - talk 16:10, 13 April 2011 (UTC)

"Big bang theory". Phewy, bah humbug, hogwash. I can think of no other scientific postulation which has received such resounding, universal acceptance based on such flimsy empirical evidence(other than perhaps the flat earth theory). Oh yes another one might be "god done it". The big bang is no more an explanation than the bible is. Think about it.190.149.154.194 (talk) 17:08, 13 April 2011 (UTC)

Perhaps I should clarify. Befor the existance of time or space or the universe,(something?) went bang and brought everything including itself into existance. What? Metaphysical mumbo jumbo.190.149.154.194 (talk) 17:21, 13 April 2011 (UTC)

Read Big bang#Observational evidence for the empirical evidence for the big bang. Dauto (talk) 17:48, 13 April 2011 (UTC)

The Big Bang theory is one of the best-evidenced scientific theories in the world, provided you understand its inherent limitations (briefly, that it describes effects and not cause). — Lomn 17:50, 13 April 2011 (UTC)

Thanks guys. I have no difficulty with hubble's expansion conclusions or with penzias and wilsons observations of residual electromagnetic radiation. I do however have a problem with the general assertion that the logical back track of those observations indicate the origin of the universe. It seems clear that what is being learned is part of the history of the universe, not neccessarily the origin. I think that basically sums up my argument.190.148.132.153 (talk) 19:07, 13 April 2011 (UTC)

I think that most (if not all) cosmologists would agree, these days. -- BenRG (talk) 20:38, 13 April 2011 (UTC)

but agine it cold be cycle in time , and be black hole agine . —Preceding unsigned comment added by 77.125.91.113 (talk) 22:35, 14 April 2011 (UTC)

Contrary to popular belief, you can put a big bang cosmos inside a larger universe that didn't start at the big bang, at least in classical general relativity. From the outside, the big bang cosmos has the same gravitational field as any other object with that mass. (This means the mass has to be finite—which means that the homogeneous cosmos that we find ourselves in has to have an edge out there somewhere—but that's consistent with observations if the edge is far enough away.) The big bang appears from outside as a white hole. In a black hole there's an event horizon that can only be crossed from outside to inside, and anything that does cross it ends up at the singularity, while anything that doesn't cross it ends up at future infinity. A white hole is the time-reversed version of that: there's an event horizon that can only be crossed from inside to outside, and anything that crosses it started out at the singularity (the big bang singularity, in this case), while anything that doesn't cross it started out at past infinity. The big bang singularity is inaccessible from the outside universe, but all of the matter that originates from it crosses the event horizon, after which there are no restrictions on two-way travel between the big bang and non-big-bang regions.

However, if there's a positive cosmological constant, then long-distance travel eventually becomes impossible. In the real world, assuming future expansion is dominated by the cosmological constant, I think that it's already too late to reach the edge of the visible universe, much less the edge of the whole big bang cosmos (if there even is one). Also, I don't know how quantum gravity alters this picture. Classically, the white hole has to have existed forever from the outside universe's perspective, but I don't see why it wouldn't Hawking-radiate away once you add quantum effects. It may be that nothing I said above makes sense in quantum gravity. (And all of it is almost certainly wrong in any case, even if it works in theory.) -- BenRG (talk) 20:38, 13 April 2011 (UTC)

Finally I love supernovae for their brightness in exploding (as many people suppose they are new ) and their rule in sending our body and our earth elements here and their heart (neutron star )which have palpitation such as our heart does

akbarmohammadzade--78.38.28.3 (talk) 04:16, 14 April 2011 (UTC)

BenRG - thank you for your response. At the risk of sounding nasty, I'm getting kind of tired of hearing it repeated ad nauseum on RD/S that "time doesn't exist outside of the big bang" (I've run into this paradigm problem when asking questions here before). It's just wrong - from the perspective inside of the big bang, time outside would not exist if I'm not mistaken (hence the white hole). But there is no reason that anything outside of it couldn't exist. Now the only question is: how would a white hole that massive appear to the outside? And what would the time scales look like? Is it even possible it might appear like a black hole? Magog the Ogre (talk) 01:53, 17 April 2011 (UTC)

you need as i imagin to divide what is happening in our condition of life and way of our sensing the time and relativistic time, and the way which do our mind think , then comparing those to find better way of imaginary,and intering to place there is no time. the subject and question brout below I think be useful for you .

. akbarmohammadzade--78.38.28.3 (talk) 03:32, 17 April 2011 (UTC)

how dos god see us ?

Imagine the piston of your car , you do start your car and run , after one hour you may go 70 KM your car weels did rotate 70000 times and motor piston moved 180000times , for you time spends slowly and for apoint on car weel middle and for a point on piston very fast. our brain thinks abslotly free from time , so the future and passed time and recent is equal for it ,we are seeing big bang and its events with ability of our strong brain and its modeling , and out standing not to be nessesery. we round earth axis one time per day , our year is 365 days , but one day for sun is 27days and one year for sun is 225 million years . there is in holy kuran that one day in after death time equals our 50000years , and the earth had created in 6 days ,of course those are not equal our recent days . we dont know troughly god's mind .and his way of creation , some things will appear to us after death . that was examined for miones reached to sea side and observed on top of hill , the time spending is very slovly for mion and its half life .(for its speed %99.9C)

akbarmohammadzade--78.38.28.3 (talk) 03:32, 17 April 2011 (UTC)

Bear pit

The article says that a bear pit trap can deter bears from approaching a cabin. How could that be? If bears are smart enough to avoid falling in it, wouldnt they be smart enough to simply walk around it? Thanks 92.15.19.232 (talk) 13:11, 13 April 2011 (UTC)

Perhaps bears are just smart enough to keep away from anything that looks dangerous or smells human, but not up to complex route planning. Here is the editthat added the information to the article Bear pit. You might leave a message to the editor on their Talk page or raise the question at the article talk page. Cuddlyable3 (talk) 13:37, 13 April 2011 (UTC)

It's unreferenced and sounds pretty questionable to me. I'd just remove it and maybe leave a note about it on the talk page. --Sean 19:32, 13 April 2011 (UTC)

What about the girzzly bear that watched its mother and probably other older siblings get killed by a hunters and then continued to watch as the hunters gathered arount the mother to take pictures with it. The juvenile bear must have watched for a while as the hunters "hugged" and "played" with the mother. Later the same hunters were back and had the juvenile in their sights when the bear rolled over on its back and played dead showing submissive behavior while slowly coming closer to the hunters. it let them pet it and touch it as if saying here do what you want but don't kill me. it was on TV and it changed the hunter's life forever. —Preceding unsigned comment added by 98.221.254.154 (talk) 02:07, 14 April 2011 (UTC)

Maybe they are so "smart" that they know if they see 1 pit in the area there is likely to be others that they might not see.98.221.254.154 (talk) 02:50, 14 April 2011 (UTC)

That's what I think was implied, but that seems a bit beyond bear intelligence, to me. StuRat (talk) 06:23, 14 April 2011 (UTC)

Not really, did you read the question? He's asking why they DIDN'T walk around the one they saw. Does the juvenile bear's behavior in my previous example also seem beyond bear intelligence to you? —Preceding unsigned comment added by 165.212.189.187 (talk) 13:42, 14 April 2011 (UTC)

I was under the impression that bears were a fairly intelligent group of animals. Googlemeister (talk) 15:29, 14 April 2011 (UTC)

Fairly intelligent yes, probably on the order of dogs. But seeing one trap and then extrapolating that there may be others requires that it think about what you are thinking ("He's trying to trap me !"), getting into game theory. This is likely beyond all but the most intelligent animals. Although I suppose there might be a way to figure it out using less intelligence. If I found something bizarre in the woods, I might look for it again in the same spot, even if I had no idea who or what caused it to appear there and what their motivation, if any, might be. Perhaps a bear can work on this level. StuRat (talk) 18:14, 15 April 2011 (UTC)

Well, I may not be any smarter than the average bear, but I'm fairly certain the implication in that article is that the pit has to go 360 around your cabin. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:41, 17 April 2011 (UTC)

Would that be called a pit ? That's more of a trench, or, if filled with water, a moat. StuRat (talk) 21:04, 17 April 2011 (UTC)

The key question is: Never mind the bear walking around the pit... how can you ensure that he will take a path that will even lead to the pit in the first place? ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:06, 17 April 2011 (UTC)

Mass-energy conversion of the human body

One of the sources I've read claims that the conversion of the human body mass to energy would produce a 200-300 TNT megaton explosion, Another source, however, states that because the basic human body components - carbon, hydrogen, oxygen and nitrogen - have low molecular weight and a lower proportion of internal energy, the released energy would be far less than that from the nuclear weapons. Which is right?--89.76.224.253 (talk) 16:17, 13 April 2011 (UTC)

My suspicion is the difference is in how you are proposing to convert the mass to energy. If you're talking about throwing a human into a human-sized chunk of anti-matter (a more or less pure conversion of mass into energy), then you'd get something like a massive nuclear explosion. If you're talking about any other, more conventional method (e.g. burning alive), you're getting considerably less than that. --Mr.98 (talk) 16:20, 13 April 2011 (UTC)

Going by the mass–energy equivalence, the human body would be around 4.5 to 11 EJ (ballpark estimate for adults - ~50 to ~120 kg). That is, very roughly, between 1000 and 2600 megatons of TNT. By comparison, the biggest bomb ever created by humans was around 50 megatons of TNT. --Link ^(t•c•m) 17:10, 13 April 2011 (UTC)

Evaporated Water Consumption

If one consumes water with absolutely no salts, what are the major disorders one might run into? Most of the disorders found in wiki and google search are caused by a single salt/mineral deficiency. Also what specifically does the body go through when there are no salts present in the water consumed? Does this affect kidneys? Is it true that salt deficiency causes body to borrow salts from bones resulting in calcial erosion of bones in process? —  Hamza  ^{[ talk ]} 17:29, 13 April 2011 (UTC)

Does this help? --TammyMoet (talk) 18:12, 13 April 2011 (UTC)

Actually, I think Water intoxication is more relevent; water intoxication is caused when consumed water causes the electrolytes (salts) in the bodies fluids to become diluted to a dangerous point. --Jayron32 18:53, 13 April 2011 (UTC)

Water intoxication can (and in practice usually does, as it's what people usually drink) involve regular tap water and mineral-containing spring water; it's not confined to demineralized or distilled water, and indeed the trace minerals present in most water don't make an appreciable difference to body or blood electrolyte levels. TenOfAllTrades(talk) 19:39, 13 April 2011 (UTC)

Note that you can get the salts you need from food, they needn't be in the water. StuRat (talk) 02:05, 14 April 2011 (UTC)

How did the hills of Rwanda form, and how old are the soils?

Rwanda is the "land of a thousand hills", but I can't work out how they were formed. In the UK, AFAIK, most hills were formed by the last glaciation - how do hills form on the equator? On a related note, can anyone find out roughly how old the soils in the south of Rwanda are (we'll be talking millions of years)? _{(google is not being my friend today)} SmartSE (talk) 18:35, 13 April 2011 (UTC)

Rwanda lies in the western branch, pretty much right under those two red triangles

Rwanda lies on the western fork of the Great Rift Valley, see the map to the right. The hills in Rwanda are thus caused by Plate Tectonics, i.e. in this case the area is literally being torn into two pieces as the Somali Plate seperates from the African Plate. Along plate boundaries, you get a lot of geologic activity, from volcanism to subduction to folding, and I suspect that, given where Rwanda is, despite being such a small country, you can find ample evidence of all of this. In geology, all of these process are called Orogeny, which roughly means "mountain birth". Sadly, I cannot find any articles on the Geology of Africa or of the Rwanda region. The template below, filled with redlinks, shows that this is likely a MUCH needed area of Wikipedia. Alas, I hear there is a new Pokeman coming out soon, so I think this is going to be pushed to the back burner for a bit longer while more important work gets done.--Jayron32 18:48, 13 April 2011 (UTC)

The geology of Rwanda is pretty complicated so it probably depends on which hills you are talking about. Generally speaking though, in the tropics like elsewhere, landforms like hills are formed by climate+the nature of the rocks+the biological activity...only much faster. Rock can be turned into soils through chemical weathering and high rainfall, transported away somewhere else either by water or landslides/soil creep/slow flow processes etc pretty quickly in the tropics. Well, that and whatever else is going on geologically that could effect the landscape like rifting, volcanic activity etc etc. Sean.hoyland - talk 19:12, 13 April 2011 (UTC)

I was going to go start linking the geography articles of those respective countries, then I realized... Not the same thing at all. Falconus^{p t c} 22:41, 13 April 2011 (UTC)

Follow-up on cleaning apple juice bottles for recycling

Referring to this question, I am happy to say I finally threw out the first of about half a dozen apple juice bottles.

Using hot water and dishwashing liquid, but mostly repeating the process of filing the bottle with water and adding dishwashing liquid and shaking it up every now and then when I prepared my bottles for recycling, I finally looked at one bottle and realized it was clean enough to go.

The others still look a mess. I suppose I could take them, but someone would have a lot of work to do and they might just reject them at whatever facility processes them.

Yes, it has been over a year. I had no idea.Vchimpanzee · talk · contributions · 18:40, 13 April 2011 (UTC)

At least you didn't send them to the recycling center Bluefist ^talk 13:26, 14 April 2011 (UTC)

It seems that you may have the wrong idea about what recycling is. It's true that if you wash out a bottle and put something else in it you can say that you recycled it, but that is not how a recycling facility does it. At a commercial recycling facility the sorted plastics are melted down and reformed into other products. Any contaminants (such as apple juice and other stuff) are iliminated by processing and melting. Therefor a simple rinse out one time with water will aid the processing slightly. It is not neccessary to make them clean enough to put food into.190.56.16.167 (talk) 20:18, 13 April 2011 (UTC)

Another thought. If your bottles are made of glass the same thing applies. The glass will be smashed up and melted down to make other bottles or maybe a window. You dont need to make them clean enough for food. Germs will not survive the melting process.190.149.154.28 (talk) 21:00, 13 April 2011 (UTC)

Where I live the recyclers say to just recycle the item without any cleaning at all, just leave remaining food or juice on it. I suspect it will get washed later anyway. Graeme Bartlett (talk) 21:39, 13 April 2011 (UTC)

My understand was the washing of recycling was more to prevent Rats or Cats or whatever other street creature from making a mess of your recycling box to get at that last bit of baked beans your tin didn't get clean (similarly to reduce smell given that my recycling is only collected once a fortnight). ny156uk (talk) 22:06, 13 April 2011 (UTC)

What is your goal? to help the environment? if so then you might want to consider all the electricity for the hot water, the good, clean potable water that you wasted cleaning the bottles, the soap you wasted and added to the once good water that now has to be removed by some water treatment facility. all because you wanted to clean some organic biodegradable material off the glass bottles? think a little farther than your nose. —Preceding unsigned comment added by 98.221.254.154 (talk) 02:17, 14 April 2011 (UTC)

I don't know what my goal is. I just didn't want to put those filthy bottles in with the regular recyclables. Ordianrily, the stuff left in the bottles will get washed out easily and the bottles will be clean. These were bottles I waited too long to wash out and they're disgusting. Maybe they would accept them. I do know if I'm not careful to clean some of the items, the perfectly good recyclables in the bin could get messed up. By the way, I didn't waste soap. I waited until the bottle of dishwashing liquid was nearly empty. I probably did waste water.Vchimpanzee · talk · contributions · 19:32, 14 April 2011 (UTC)

I'm surprised you responded to the IP's "think a little farther than your nose" comment. I'm sure the environmental impact of the equipment and infrastructure he used to post that comment far exceeded your bit of water and soap. Sean.hoyland - talk 19:58, 14 April 2011 (UTC)

That's stupid. Nobody bought a computer just to reply to this post.

The goal here presumably isn't to put the bottles in the recycling bin. The goal is to make a positive impact by doing so as opposed to throwing it in the trash. (By saving glass.)

98.221 made a perfectly valid point that water and energy have been wasted in the attempt to save a little glass. APL (talk) 15:07, 15 April 2011 (UTC)

I could be wrong, but it seems unlikely your recyclables are kept separate when they leave your bin. In other words, it doesn't really matter how clean your recyclables are, they're going to get 'messed up' by other people's recyclables... Nil Einne (talk) 20:40, 14 April 2011 (UTC)

I'm surprised they don't make an effort. We have a giant container we throw all the recyclables in. At one time the different types were separated. I don't have a bin of my own because recycling is a recent introduction in my community. I still take everything 'to the dump" as I always did. If I asked for a bin like my neighbors have, I'd have to remember to put it out every Monday. Chances are I wouldn't.Vchimpanzee · talk · contributions · 22:50, 14 April 2011 (UTC)

For those who may wonder, my father took the trash on Saturday, and at some point I started going with him but it was always after lucnh. I'm still in the habit of going at that time or, if the college library near my house is closed, later in the day. The recyclables go in what look like milk crates. I'm not sure how we started doing that. Once the town got trash pickup, I chose to keep doing what I always did, even after they added recycling pickup.Vchimpanzee · talk · contributions · 21:13, 15 April 2011 (UTC)

Do we feel heat from the sun because of Infra Red, or because of the energy in the entire spectrum?

Whenever people talk about being warmed by infra red radiation from the sun, I always grumble and say that the entire spectrum of light contains energy, and that infra red just happens to be the frequency that warm bodies on earth emit, and so we think of that as heat.

However, I recently read in [3] that "Far infrared waves are thermal. In other words, we experience this type of infrared radiation every day in the form of heat." So this NASA site seems to be saying that there really is a difference between IR light and other light when we are feeling heat from the light source. Is that right? Have I been confused all along? Can we not get warm from just the visible/UV spectrum of the sun (if there is enough of it)?

Thanks! — Sam 71.184.188.110 (talk) 22:30, 13 April 2011 (UTC)

You are not wrong. The sentence you quoted is about perception, we experience some frequencies as vision, and others as heat. But both can cause warming. However there is a somewhat more light energy available as infrared than as visible light (from the sun), so most warming is from the infrared. Ariel. (talk) 22:41, 13 April 2011 (UTC)

But you can have very bright, but "cold" light right? Vespine (talk) 22:44, 13 April 2011 (UTC)

I think the reflectance characteristic of each frequency is very relevant. See Spectral reflectance curve. The frequencies we associate with visible light are readily reflected from opaque surfaces and that is one of the reasons we can see things with the naked eye, but little of the energy with those frequencies is transmitted into the opaque surface to raise its temperature. The frequencies we associate with the infra-red band are not so readily reflected from opaque surfaces so most of the energy in the IR band is transmitted into the opaque surface and so raises its temperature. Also see Infrared#Heat and Thermal radiation. Dolphin (t) 22:55, 13 April 2011 (UTC)

The so called "cold" light is a light bulb that produces little Infrared while producing visible light. Of course, visible light is also a form of heat so "cold" light does produce heat. Dauto (talk) 23:58, 13 April 2011 (UTC)

"But you can have very bright, but "cold" light right?" Not if the source is blackbody radiation. The spectrum emitted because of thermal energy is a well-defined function, and the intensity is rigidly bound to the frequency-distribution. Both of those parameters are determined by the source object's temperature.

A non-thermal source of radiation can provide any spectral distribution; it can radiate at specific frequencies (observable as individual spectral emission lines), or can radiate over a wide range of frequencies, with continuously varying intensities.

But again, if the source is due to thermal emission, then the total amount of energy radiated is defined by the temperature of the source (which also defines the spectral distribution that gets radiated). The mathematical formula that defines this relationship is Wien's displacement law. Loosely speaking, it's not possible to have very bright radiation from a very cold source: decreasing the temperature decreases the total amount of radiated power and changes the shape of the spectrum. Nimur (talk) 00:17, 14 April 2011 (UTC)

Just as an aside - "cold" lightbulbs, such as a cold cathode fluorescent lamp, are not thermal radiators: they fluoresce (producing photon-emission via a totally different physical process), and thus are not a blackbody radiator. This is very different than an incandescent lightbulb. Nimur (talk) 00:20, 14 April 2011 (UTC)

Not if the source is blackbody radiation But we're not talking about "the source", we're talking about the "light" it self. if you have some IR and heat shielding that transmits only visible light, then that light can be bright and "cold" right? As in if you shine it on a thermometer it won't heat it up? Vespine (talk) 02:00, 14 April 2011 (UTC)

The only thing that matters is the total irradiance, and how well light of that wavelength is absorbed. If a surface has equal absorptivity for visible light and infrared, then a 1 W beam of infrared will heat it up exactly the same as a 1 W beam of visible light. Talking about light being "cold" is meaningless.--Srleffler (talk) 02:38, 14 April 2011 (UTC)

Correct. The mathematical model of color temperature is an attempt to fit a black-body curve to a light-source. But if the light source isn't black-body-like, then its effective temperature has very little physical meaning. Nimur (talk) 02:49, 14 April 2011 (UTC)

Heat is the sum of all of the kinetic forms of energy experienced by a molecule, these are usually classified into 3 types of motion: translation (that is, moving in a straight line), rotation (spinning around an axis) and vibration (deformations of the molecule along bonds). Photons in the IR range cause molecules to vibrate, basically by exciting the electrons that occupy the molecular orbitals that hold the molecule together. The article and section Infrared_spectroscopy#Theory and stuff in that area describes how IR photons do that, and the various ways that a molecule can vibrate. Here's the important connections to make, for the layperson: Vibration of molecules is heat. Its not that we "perceive" it as heat, it not that we "sense" it as "warmth" or anything like that: vibration is heat. Since IR photons cause electrons to become excited in such a way as to cause molecules to vibrate, quite literally IR light causes heat. In a very direct sense, by the most basic definition of what heat is. --Jayron32 02:23, 14 April 2011 (UTC)

But visible light and UV cause heat too. Anytime electromagnetic radiation is absorbed in a material, the result is heat.--Srleffler (talk) 02:38, 14 April 2011 (UTC)

Not necessarily. Absorbed light will always cause electronic transition from one quantum state to another. However, this transition does not necessarily cause the substance to gain thermal energy. Thermal energy (heat) is only that energy that involved increases in kinetic energy of the molecules themselves; an electron moving to a higher energy quantum state does not necessarily cause the molecules of the substance to move faster; it MAY cause that to happen, but only in situations where there is significant coupling between, say, electronic states and vibrational states (vibronic coupling). Absorbed light may cause other things to happen as well, such as chemical reactions (Homolysis being a major one), fluorescence, phosphorescence, or simply immediate re-emission of the same wavelength photon. --Jayron32 04:07, 14 April 2011 (UTC)

Jayron, you're making the very common mistake of confusing the word heat (which is energy transferred to a substance by a variety of methods including radiation - IR, UV, visible, etc, all included) with the internal kinetic energy. Besides, most of the visible light that is not reflected and does get absorbed eventually does find its way into the vibrational modes of the molecules. Dauto (talk) 14:52, 14 April 2011 (UTC)

Procession of the Perihelion

Prior to the acceptance of GR what other attempts had been made to explain the peculiar mercurial motion. So far I have:

1. Planet Vulcan
2. Gravity as an $r^{2.00000016}$ instead of $r^{2}$ law

Please add to the list if you know of any! Thanks. —Preceding unsigned comment added by 92.20.205.185 (talk) 22:46, 13 April 2011 (UTC)

For one thing, gravity is a $r^{-2}$ law, not a $r^{2}$ law. (Sorry for the nitpicking). Dauto (talk) 00:07, 14 April 2011 (UTC)

Why not at all, Newton claimed the source mass required to produce a unit force on a test particle at a distance $r$ scaled as $r^{2}$. —Preceding unsigned comment added by 92.20.205.185 (talk) 00:46, 14 April 2011 (UTC)