Wikipedia:Reference desk archive/Science/2006 August 7

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Megawatt Battery[edit]

Is it possible to build a rechargable battery that could hold a Megawatt or more?-- 00:09, 7 August 2006 (UTC)

EDIT'D because someone mistakenly put their question here, eh? Vitriol 00:50, 7 August 2006 (UTC)
A megawatt is a measure of power and you cant hold power in a battery. Howver if you mean megajoule which would give 1 MW for one second, then it should be possible by connecting lots of small batteries together. Why would you want to do such a thing anyway?--Light current 01:05, 7 August 2006 (UTC)
It would have many uses, such as for a rail gun or coil gun. StuRat 06:52, 7 August 2006 (UTC)
In that case you need large HV capacitors (the ultimate rechargeable) rather than batteries. 8-)--Light current 11:51, 7 August 2006 (UTC)
They built a 40 megawatt NiCd battery in Alaska in 2003. See --Heron 20:48, 7 August 2006 (UTC)

1 million joules is easily held in a typical car battery, and is a relatively small number compared to what's typically used in commercial UPS applications. A common large scale UPS configuration will have 200 or more batteries, together capable of discharging up to 1MW each second, for up to 15 minutes, amounting to almost 1GJ of energy. Did you mean for it to be portable? --Jmeden2000 21:46, 7 August 2006 (UTC)

And how large is this GJ battery pack?--Light current 02:10, 8 August 2006 (UTC)
Imagine a whole room full of batteries, and then double it :-) --Jmeden2000 15:16, 8 August 2006 (UTC)

Persactly! That Y I suggested HV capacitors.--Light current 15:22, 8 August 2006 (UTC)

Too bad there isn,t one the size of a car but thanks alot for the help.

Ahh, now I see where youre coming from! What about fuel cells?--Light current 19:23, 8 August 2006 (UTC)

Wouldnt you need a bunch of fuel cells to produce 1 Million Joules? A car sized battery or device that could produce power in the millions of joules would be perfect for spacecraft, using possibly Ion Thrusters or some sort of electrical thruster.

Dont ask me -- look at the page! 8-)--Light current 21:23, 8 August 2006 (UTC)

Septic System[edit]

I can't seem to grasp the workings of a septic system

If I use DIAL soap, and dial soap is anti-bacterial, as is most of the laundry detergents on the market, doesn't that cause the septic system to shut down?

Why aren't there enough "bacteria" in the human by-products going into a septic tank so that you don't have to add an additive of more bacteria?


You shouldn't have to add any kind of additives to a properly-functioning septic system. The enzyme treatments and other things sold to be used in septic systems are not really necessary. The things that cause a septic system to fail are pretty simple mechanical failures: Over time, the indigestible solids will accumulate in two places- as a floating scum layer, and as solids that sink to the bottom. Given enough time the scum layer can become very thick, and the solid layer at the bottom can also become very thick, and so the 'working space' below the scum layer and above the solids becomes too thin to be effective.
If the baffles fail, then it's possible for the scum layer to drain down into the drain field, where it may plug up the orifices in the laterals, severely affecting the ability of the drain field to function. So having the system checked, inspected, and pumped out every five to ten years will greatly help it to keep working. You don't say if it's a gravity system or a pressurized system; gravity systems tend to fail over time because the flow rate through the drain field is very low. It's not hard to inspect a septic system, doing a google search will point you in the right direction; a couple simple tools and some time and you will be able to check your system out.
I almost forgot to answer your original question: Yes, excessive use of antibacterial products may cause harm to your septic system. The key words are 'excessive' and 'may'. Normal use seems to be fine, just don't go overboard. For additional reading, see pages like this one . 04:00, 7 August 2006 (UTC)
You don't need to add bacteria because they are quite capable of doing that themselves through reproduction. And unless you throw in huge amounts of antibacteria, they shouldn't be hurt too much. Bacteria can take quite a beating. DirkvdM 08:47, 8 August 2006 (UTC)

hang-drying clothes indoors with A/C[edit]

If I have my air conditioner on, and I hang up my wet clothes indoors to dry, I figure I'm essentially asking the A/C to do the work that the dryer would otherwise be doing, and in theory it might take the same amount of energy. But what about in practice? Considering the different technologies and drying times, would one process (A/C vs. dryer) would use more energy than the other, or would they be about the same? Thanks. --Allen 00:48, 7 August 2006 (UTC)

I don't know if this is any better than just having a fan blowing on the clothes.
It is better, becuase an A/C (or a dehumidifier) will remove the moisture from the air leading to quicker drying. A fan would just tend to make the air more humid, reducing its drying potential. 8-)--Light current 14:31, 7 August 2006 (UTC)
How does a fan make the air more humid? DirkvdM 08:50, 8 August 2006 (UTC)
By transferring the water from the wet clothes into the air of course!--Light current 11:26, 8 August 2006 (UTC)
The primary function of an airconditioner is to cool the air, which doesn't help in this case. If it's so hot outside that you need an airconditioner, then why not hang your clothes outside? DirkvdM 08:50, 8 August 2006 (UTC)
It could be raining outside but hot inside 8-)--Light current 13:23, 8 August 2006 (UTC)
The action of cooling the air also dehumidifies it as the water condenses on the cooling coils!--Light current 11:48, 8 August 2006 (UTC)
Exactly, Light current. It often rains in the afternoon in Tennessee, even on the hottest days. So if I hang my clothes on indoor drying racks instead of using the dryer, I'm curious to know whether I'm conserving energy or just inconveniencing myself. --Allen 04:03, 9 August 2006 (UTC)
Depends on the comparative efficiencies of the AC unit and the drier. 8-) You dont say what sort of drier it is. --Light current 11:01, 9 August 2006 (UTC)

Hot mirrors[edit]

Today it was rather warm (say 25 celsius) and humid. This afternoon, I was standing about 0.7 m in front of some large mirrors for a long time (playing a gig actually). I noticed that it felt considerably hotter infront of these mirrors than in other parts of the room or even outside. I initially thought it was the IR from the surroundings reflecting but since IR cant travel thro normal glass, I remain puzzled. 8-? Any suggestions as to the cause of this phenomenon? --Light current 01:13, 7 August 2006 (UTC)

See solar cooker. Rangek 01:23, 7 August 2006 (UTC)

Yeah thanks for that, but those cookers use no glass. I was cooking in front of glass! Also, it wasnt sunny-- complete cloud cover.--Light current 01:37, 7 August 2006 (UTC)

No glass? Read a little more closely. Almost all of them are made of glass/mirrors. Even when it is completely cloudy there is still lots of solar radiation reaching the surface. Rangek 02:04, 7 August 2006 (UTC)

Yeah OK, but theyre using high intensity visible light energy from the sun. THere was not much light in the room and IR cant pass thro the glass to be reflected by the silvering on the back of the mirrors. Mirrors can reflect IR if they are front silvered (or just a shiny bit of metal)--Light current 02:15, 7 August 2006 (UTC)

So were talking solar radiation that can:

  • pass thro clouds,
  • pass thro the glass,
  • get reflected from the silvering,
  • pass thro the glass again and
  • irradiate me on my back so I feel hotter.

Is that what youre saying? If so, what sort of radiation would that be? Would it be the near IR, and if so can you feel it as heat?--Light current 13:15, 7 August 2006 (UTC)

Is this a sort of space blanket effect?

Can I ask where it is you live that it's only 25 degrees Celsius? Southern hemisphere? Iceland? Seems most of the northern hemisphere is in the throes of a long-lasting heat wave. Today is a cool day where I'm from and it's supposed to hit about 30 Celsius. --Ginkgo100 talk · contribs · e@ 20:50, 7 August 2006 (UTC)
The northern hemisphere is slightly bigger than where you live. :) The heat wave in Europe is long over. DirkvdM 08:56, 8 August 2006 (UTC)
Okay. The last I had heard, Europe was still suffering. The veiled insult was unnecessary. --Ginkgo100 talk · contribs · e@ 18:07, 9 August 2006 (UTC)

Its the UK. And maybe it was 27 or 28 Celsius. I didnt have a thermometer handy!--Light current 01:42, 8 August 2006 (UTC)

I suspect you are thinking of UV not easily passing through glass. --Seejyb 22:15, 7 August 2006 (UTC)

No Im thinking of IR. UV can pass thro glass I believe. Think of greenhouses! 8-|--Light current 01:42, 8 August 2006 (UTC)

No, UV is blocked by most common glass. That is why it is nearly impossible to get a sun burn in a car with the windows up and why quartz cuvettes are used for UV spectroscopy. See Ultraviolet-visible spectroscopy#Ultraviolet-visible spectrophotometer. Rangek 03:14, 8 August 2006 (UTC)

Ahh it must be visible light that passes thro glass in a greenhouse then and gets converted ito far infra red?--Light current 03:24, 8 August 2006 (UTC)

Actually, it turns out that has very little to do with how greenhouses work. See greenhouse. It turns out it isn't so much that the greenhouse is trapping the radiation, but it is just not letting the hot air drift away. Rangek 18:29, 8 August 2006 (UTC)

And the hot air being above absolute zero emits radiation- yes? seeWein's laws. If this radiation can escape thro the glass then the heat will not be retained. What is the wavelength of the radiation at 300 K? and can it pass thro greenhouse glass -- that is the question! 8-|--Light current 19:44, 8 August 2006 (UTC)

Any chance it has nothing to do with the mirrors? Was there anything else about that spot? Maybe less air current (the back of a room?). And you were doing a gig, so were there any lamps pointing at you (although I doubt you would have missed that option). DirkvdM 08:56, 8 August 2006 (UTC)

Dont think so. There were 3 lamps each of 60W spaced at about 1.5 m between the mirrors. As this power was only equivalent to that generated by about two persons, I decided that this could be ignored. It felt like a few hundred watts on my back. Also i was standing in the center of the mirror (not in front of any of the lamps). Also it felt like radiation, not warm air.--Light current 11:33, 8 August 2006 (UTC)

Some confusion here. Glass normally absorbs UV; Reflects a lot of IR (feel the reflection from an ordinary glass pane when you shine an IR light on it; maybe you would have felt the same heat standing in front of unmirrored glass, especially if you were wearing black). But definitely transmits some IR. Herschel discovered IR by transmission through an ordinary glass prism - there was something measurably hot coming through beyond the red end of the spectrum, and the heat he measured was more than that from the red part coming though the glass of the prism. Most optical cables use IR for transmission - once the light is in the glass fiber, with not as much being absorbed as shorter wavelengths would, it is tranmitted better than visible or UV light of the same initial energy. If you put an IR lamp in front of an ordinary glass pane you can feel the reflection of heat. "Ordinary" 35mm cameras can take quite effective IR pictures with "ordinary light" lenses, using IR sensitive film - the focus has to be compensated for, but some lenses have IR markings on them. --Seejyb 01:13, 9 August 2006 (UTC)

OK this makes the most sense yet. So I was getting about twice the radiation that I would have got if there had been no mirror and just the brick wall? Hmm -- interesting!--Light current 03:01, 9 August 2006 (UTC)

Plane on conveyer[edit]

Why there's no article about that famous plane on conveyer that some mistakingly claim won't take off? It was twice on Straight Dope with two conflicting answers on 03.03.2006 and 03.04.2006 and that alone makes it notable. By the way, the plane will fly off with wheels sliding all the way, contrary to the second article :)

The two articles are [1] and [2]. I'd like to take the position that the second article is correct: the conveyor belt can be rigged so that the plane does not take off. Just as the plane starts moving forward, you speed up the belt so that the plane nudges back where it was one second ago. Keep doing that, and you get a balance where the friction of the wheels causes a backwards force that exactly balances the forward force of the plane's engines. Zero net force, no movement. Weregerbil 07:32, 7 August 2006 (UTC)
But if lift is generated by air moving over the areofoils, and there is no air moving over the areofoils due to the wings not moving through the air, how can the plane take off? -- 14:29, 7 August 2006 (UTC)
Right. In one interpretation the question can be reduced to: Will the plane pick up enough absolute speed? If we manage to keep the plane in place by increasing the belt speed more and more, the wheels will also spin very fast and eventually generate so much heat through friction that the axle melts, or else the wheels come apart by the centrifugal forces. If we assume idealized components not subject to such mundane effects, you have to be very precise about which parts of physics are still operational. If the plane remains stationary while the belt moves extremely fast, the belt will drag air along and cause so much wind that the plane still gets sufficient lift. And so on ...  --LambiamTalk 16:23, 7 August 2006 (UTC)
If we have a real plane its engines have finite maximum power, so at some point the speed of the belt stabilizes and significant air flow from the belt doesn't necessarily need to happen. Or maybe it will. This could be one of those things that needs to be tried in practice. How do you go about suggesting things to the MythBusters? :-) And no wimping out by using a small model plane. Weregerbil 16:43, 7 August 2006 (UTC)

Lift requires that the plane be moving in reference to the air, not the ground. --mboverload@ 00:31, 8 August 2006 (UTC):

Echo mboverload--Light current 03:11, 8 August 2006 (UTC)

I've seen this question beat to death dozens of time on the internet. I like this discussion the best at physicsforums [3]. — [Mac Davis] (talk)

float glass[edit]

What is float glass? And what is the russian translation for it? Inna.

Our page entitled Float glass is probably a good place to learn what it is. DMacks 05:57, 7 August 2006 (UTC)

I suspect that in Russian you can use полированное стекло ("polished glass") or for an audience of experts simply флоат-стекло. --LambiamTalk 08:26, 7 August 2006 (UTC)


Photons have no mass, yet they can exert radiation pressure(mass-mass interaction involving change in momentum?

Yes. Radiation pressure --GangofOne 06:30, 7 August 2006 (UTC)
Yes. While they do not have any mass, they nevertheless have momentum (given by h/λ, where h is the Planck Constant and λ is the wavelength of the photon).

>>This one took me eight years to figure out, 'And yes Photons at times do indeed have mass', refered to as rest mass, but there is really no difference, it's just the termanology. I will give you a hint; photons as electromagnetic energy have no mass, and can even travel through two slits at the same time ( ie. the dual slit experiment). Yet durring an interaction (such as striking a white or black piece of paper), like an inferometer their velocity is no longer the speed of light, and they are no longer electormagnetic rediation but a particle that has mass aquired from the conservation of evergy. This is only a hint, It seems to be from my experience a close held secret, at least for undergraduates. Other clues in space time energy fluxuations cause mass to "pop" out of energy, then the mass transfers back to energy. Also in a clyclatron durring a collision there are particles with mass that have a spiral trajectory in an electromagnetic field, but are short lived before they "disaper or transform into energy." It goes both ways Also They Do Have Mass When Transfering Momentum!.-- 12:52, 7 August 2006 (UTC)aaron.

When you talk about the rest mass of the photon I assume you mean (hf)/c² (or p/c). I don't believe that is of any consequence in this question, although a good means of explaining where photons get their momentum from.

Yes the rest mass is relative to this question, It is the mass of the photon when it exist as a particle!Durring an interaction. The Photon acctually has the mass of the rest mass, for a brief period of interation! aaron-- 14:02, 7 August 2006 (UTC)-- 14:02, 7 August 2006 (UTC)

>>>Do I need to repeat the old adage of photons at times behave as electromagnetic radiation and at other times as a particle. Think about it, I believe I have explaned it, if you don't understand, quit trying>>>Photons durring interactions are particles with a mass equal to their rest mass. Look up the interaction tables! aaron-- 14:22, 7 August 2006 (UTC)

When I say I don't think it's of any consequence, the question didn't ask for the mechanisms by which momentum was exchanged. The effects are described well enough by whoever gave the second answer. I can assure you I do understand wave/particle duality, I did do a PhD in quantum computing.
Sorry but I felt that the mechanisms by which momentum was exchanged was relavent to the understanding of the original question, in my opinion. I trust you opinion and your understanding, but since the question stated that photons have no mass in my opinion it was relative. Again Im sorry. aaron-- 15:01, 7 August 2006 (UTC)
That's quite alright. I generally hesitate to use the term 'mass of a photon' because, while they may have mass during an interaction, it is only for a very short time and time and energy/mass are non-commuting variables.
What about reading our article Photon? Photons have energy and therefore also have mass in the usual sense of gravitational mass. The usual meaning of "rest mass" is the mass at zero speed, which is meaningless for photons, but using the formula for relating (relativistic) mass with rest mass, you find a rest mass for photons that is zero, zilch, nada. --LambiamTalk 16:33, 7 August 2006 (UTC)
Yes you are correct the rest mass of a photon is a misnomer, since it can never be at rest, it is an old term for it's mass at non relativistic speeds. But durring interactions when it is a particle it does have mass, read the article photon and you will find an approximation for a photon's mass. Not rest mass but mass -- 17:50, 7 August 2006 (UTC)aaron
The term 'rest mass of a photon' is a useful (if rather antiquated) terminology for explaining radiation pressure. Mathematically it comes from the energy of a photon, E=hf and E=mc² and gives m=(hf)/c²

>>Yes mathematically, but the truth of the matter is that it is a particle for a brief period of time durring the interaction, it is a actually a partical with mass that is not traveling at the speed of light; and this does come from the energy of the photon, which is transformed into mass. Which may or may not transforme back to pure energy with no mass, travaling at the speed of light--Aaron hart 07:22, 8 August 2006 (UTC)

See optical tweezers. -- SGBailey 22:28, 11 August 2006 (UTC)

Black holes[edit]

How come black holes have two beams of energy?

The polar jets or relativistic jets don't come from the black hole itself, but rather from the accretion disk around a black hole. StuRat 06:46, 7 August 2006 (UTC)
But to answer the question, nobody knows Philc TECI 15:12, 7 August 2006 (UTC)

large low density rock?[edit]


I have found a rock that is 1235 cm^3 and weighs only 148g, this gives it a density of .12g/cm^3. Is this just a large size of unusual pumace. It has a honycomb sturcture on the outside, but under an ultraviolet light, there is a distinct differece (as in two distinct layers, like the bottom side was heated to a much higer temp. than the top. Also on the top there is a bump with the lighter grey comming from the tip to the bump, and then it darkens,) I can see how the heat has effected it, turning it a lighter grey?? It is black to dark grey any coments?? aaron-- 14:38, 7 August 2006 (UTC)

Could it be a chunk of an artificial building material, like foamed slag concrete, pumice concrete, or expanded shale? Femto 15:13, 7 August 2006 (UTC)

>>No it was found out in the woods on the top of a hill, It is definatly all natural, Thanks for the advise though.

Pumice is a good idea. --DLL 19:28, 7 August 2006 (UTC)

The density of Pumice can vary quite a bit but I've never heard of a sample that light before. The range is usually somewhere between 0.6g/cm³ and 1.2g/cm³. Where do you live? Do you have a picture of the rock that you could post? --Nebular110 19:33, 7 August 2006 (UTC)

Honeycomb structure? Is it a nest of somesort? Wasps make very light nests... Isopropyl 00:00, 8 August 2006 (UTC)
Did you find this in the debris field of Space Shuttle Columbia? --LambiamTalk 02:09, 8 August 2006 (UTC)
Yes I can post a picture, if I can find out how, and no it is not a nest of somesort, it's almost like a carbon structure, I will attempt to upload a photo, if unsucessful I will post my email and I will send it to you. aaron-- 03:32, 8 August 2006 (UTC)
This rock was found in Shasta County, ca. on the top of a hill, and yes the density is aporxamatly .12g/cm^3 I believe this to be rare, Please reply--Aaron hart 07:02, 8 August 2006 (UTC)aaron
It looks like scoria, but I think that would typically have a higher density; I don't know the range. Tuff can be very light, but usually doesn't look so rough. I think that also applies to cinder, which however can be so light (according to our article) that it even floats on water, so that aspect fits. --LambiamTalk 07:57, 8 August 2006 (UTC)
Looks like the carbon left over after the dehydration of a sugar, can that happen naturally? Philc TECI 12:21, 8 August 2006 (UTC)
Looks like a large piece of coke (coal with all the hydrocarbons removed leaving only pure carbon) Can you see any pores in it. Cant tell from photo--Light current 13:46, 8 August 2006 (UTC)
Could it possibly be extra terrestrial?--Light current 14:06, 8 August 2006 (UTC)
According to [4] there are no lightweight meteorites. Femto 15:13, 8 August 2006 (UTC)

Aaron, forgive me if I sound patronizing, but are you sure you got the weight right? Any silicate is going to have a local density of ~2 g/cm^3. Pumice and other volcanic rocks can lower their bulk density by incorporating air pockets and voids, but your pictures shows no evidence of voids intersecting the surface. Similarly, with the dimensions shown, it couldn't have more than a few millimeter thick shell of silicate, in which case I'd expect it would have been so fragile that it would long ago have broken. At less than 200 g, even a decent wind should be able to blow it around and smash up the thing. If it really has the density you say, my only conclusion is that it can't be a rock, and is likely to be synthetic. What is the texture like? Is it rough? Squishy? My guess might be some sort of weathered packing foam. Dragons flight 14:45, 8 August 2006 (UTC) >> Yes the mass not the weight is 148g. And I really doubt that it is packing foam, I guess I will have to take it to the local colledge, and then I will let you know. its tecture is very hard and brittle, pices come off of it every time I pick it up.--Aaron hart 14:51, 8 August 2006 (UTC) but you may be correct, we shall see, maybe I found something rare?? >>Forgive me I checked very accuratly and the mass is 147.2g--Aaron hart 15:01, 8 August 2006 (UTC) also it is full or pores, and I can tell that the crust is more than a few mm thick. But it may be synthetic, just seems ood to find it on top of a hill in the woods.--Aaron hart 15:04, 8 August 2006 (UTC)

Strange. Did you break it open to see what the inside is like? Is it mostly hollow maybe? Were there other specimens similar in the area or did it look totally out of place on the top of the hill? --Nebular110 17:43, 8 August 2006 (UTC)
It would be good if it was a new stone; they could call it Hartstone! smurrayinchester(User), (Talk) 21:48, 8 August 2006 (UTC)

Two Cars in a Head-On Collision[edit]

In my game PGR3 (in which I find the physics very unrealistic) I was going to run in to my brother in a head on collision. I was going 207 mph and he was going 183 mph. With the physics like they are, the cars collided and not a whole lot happened. My question is, how much power would that exert? I'm not real smart about Physics, but I remember the Law of Conservation of Energy and that the energy is still there, you just don't see it(?) and all the energy those cars had were almost immediately gone. I hope someone understands my rambling here. Thanks. schyler 12:04, 7 August 2006 (UTC)

Without knowing the game I guess they may be simulating the energy absorbing features of the cars and they just crumple up. THe energy is used in deforming the metal, creating sound etc but all the enrergy finally ends up as heat if both cars are at rest. THe kinetic energy of each car is 0.5 mv^2, so you could work out how much energy was dissipated in the crash (assuming both cars are at rest afterwards).--Light current 13:23, 7 August 2006 (UTC)
Also unlike Kenetic Energy the momentum for the two cars before and after is absolutly conserved, Kinetic Energy is also conserved but takes on other form. But The momentum before and after the collision are the same. Momentum=mass*velocity so if they came together at a complete rest, without one or the other moving backwards, the masses of the two cars must be different, in other words v1m1=v2m2. In a system Kinetic energy is transformed into deformation, heat, sound etc. and as stated earler end up as heat. But momentum is conserved without transformation into other forms. Although after both cars come to a rest there is frictional momentum that is transformed to the earth. aaron-- 13:33, 7 August 2006 (UTC)
Energy of deformation is not all dissipated through heat. It takes work to "lift" the metal into its new position just as it would to lift a weight through gravity or push a weight against a spring. Heat and strain cause most of these springs to fail, but a small fraction of this "spring potential" remains stored in the twisted metal. (talk) 02:32, 12 May 2008 (UTC)snn 12:30, 7 May 2008 (UTC)
You are right about the shoddy physics, especially with respect to collisions. Most driving games don't bother with them since its little or no fun to watch a car turn into 'not a car' and then require the player to start over. The question I think you should be asking (since you probably know that you are just dealing with two huge quantities of kinetic energy) is 'where would that energy go to?' Objects collide and one of two things happen to the kinetic energy, a) An elastic collision where kinetic energy is conserved and b) an inelastic collision where kinetic energy is converted into internal energies. Since cars are quite dynamic there would be a combination of these two as the various metal and plastic bits met head on. Much of the energy is 'gone' into another form such as heat, as the metal in each chassis takes on a dramatically different form. Some energy may come back kinetically and one or both cars will continue moving after the collision, or (more likely) many small bits from each would keep moving. --Jmeden2000 21:17, 7 August 2006 (UTC)
It's not a physics answer, but the reason why the cars don't suffer a whole lot of damage/body deformation in the game is because the car manufacturers, who licence their cars for use in the game, don't want their brand associated with mangled wreckage, etc. (or so rumour has it). On the other hand, a game like FlatOut which uses generic unbranded cars can mangle the bodywork all it likes. Sum0 23:33, 7 August 2006 (UTC)

>> Also in deformation of the cars there energy put into the deformation, but also this creates a large amount of heat, The Physics may be shoddy, but sugesting an elastic collision, with cars, come on now! aaron--Aaron hart 07:14, 8 August 2006 (UTC)

Did you even read my entire reply? Just curious, i know i tend to ramble sometimes but i did get everything in there i intended to --Jmeden2000 15:12, 8 August 2006 (UTC)

>>A perfectly elastic collision is defined as one in which there is no loss of kinetic energy in the collision. An inelastic collision is one in which part of the kinetic energy is changed to some other form of energy in the collision. Any macroscopic collision between objects will convert some of the kinetic energy into internal energy and other forms of energy, so no large scale impacts (ie larger than atoms, or molecules); are perfectly elastic--Aaron hart 07:04, 9 August 2006 (UTC) I do remember a little from college. For a possible elastic collision occuring, solids from the car body, must vaprorize into a gas, then it is possible for these two gasses to have a perfectly elastic collision, But this would be quiet neglagable, and would not even beging to be able to be calculated!--Aaron hart 07:15, 9 August 2006 (UTC)


hi im a student of psg biotech....can anyone say how to estimate the density of spores like vegetative spores or especially the spores of bacilus subtilis.....give some detailed explanations....

Sounds like homework. I'd try a PubMed search for bacilus subtilis spore density and follow the protocols given in the articles. -- Scientizzle 18:15, 7 August 2006 (UTC)
I would use a hemocytometer myself.Tuckerekcut 21:02, 7 August 2006 (UTC)

Microwaves Lose Power After 15 Minutes Use?[edit]

In the microwave article, it says that after 15 minutes of use, the power of the microwave drops off - is this true? What is the cause? The text in question can be found at the bottom of the section which this link leads; Microwave oven#Uneven heating, deliberate and not

It it is true, which it may well be, then it is a mechanical effect of the microwave oven, not with the microwaves themselves. -- 18:51, 7 August 2006 (UTC)
The magnetron gets less efficient as it heats up. There is a link in the microwave article that used to explain this, but it is now a dead link. --Heron 20:38, 7 August 2006 (UTC)
Yes, and not necessarily after 15 minutes, I would assume. --Proficient 12:09, 10 August 2006 (UTC)

Pocket PC emulator[edit]

Can I run Pocket PC programs on Microsoft Windows using an emulator? -- Toytoy 14:21, 7 August 2006 (UTC)

I think that the answer is yes, that's why emulator design is for. Now, does such emulator exist, and did you try any search engine with the terms of your question ? -- DLL .. T 18:49, 8 August 2006 (UTC)
I believe that there is a Pocket-PC edition of Microsoft Visual Studio, which includes exactly such an emulator, as well as a Visual C++, Visual Basic, and other Microsoft programming environments/compilers for pocket-pc's. Are you a software developer, or just an end-user trying to use a PDA tool on your desktop? If the latter is the case, you may find a workaround using conventional desktop software for the same task. Nimur 19:39, 8 August 2006 (UTC)
I want to run MetrO on my Windows computer. I don't know why this program does not have a Windows version. -- Toytoy 05:55, 10 August 2006 (UTC)

A warm sun[edit]

Why does the sun feel warm when youre exposed to it? Its a serious question.--Light current 14:27, 7 August 2006 (UTC)

All electromagnetic radiation (including light) is just a form of energy. When the light hits your skin, some of it is reflected and some is absorbed. The energy in the light which is absorbed has to go somewhere (see Conservation of energy) and becomes heat energy. All light, natural and artificial, will transfer some heat energy to a surface it hits (as long as that surface isn't perfectly reflectant). -- Plutor 14:38, 7 August 2006 (UTC)

So you can get warm just from visible light?--Light current 14:40, 7 August 2006 (UTC)

>>yes; aaron-- 14:49, 7 August 2006 (UTC)

OK thanks for shedding some light on the problem! 8-))--Light current 14:51, 7 August 2006 (UTC)

So do your eyes get warm when you look at things? I thought it was only glassblowers who got cataracts. 8-)--Light current 21:16, 8 August 2006 (UTC)

The sun is just a big firebrand. Visible light must take a very little part in the heating. Non-visible radiation (infra red) is also absorbed by the skin and diffuses to the body, it heats more accurately. --DLL 19:24, 7 August 2006 (UTC)

What do you mean by firebrand?--Light current 02:23, 8 August 2006 (UTC)

Well, he probably doesn't mean that the sun is made up of a bunch of cartoon characters, or that the sun is a burning ball of fighter planes so it's safe to assume maybe he meant that the sun is something that's on fire, like a giant bunch of burning wood.
Funny, 'brand' is Dutch for fire. What is the etymology of the word? DirkvdM 09:17, 8 August 2006 (UTC)
According to Webster's and Livestock branding, brand had meanings of hot stick/torch/sword in Middle English. I think I've seen -brand being used in sword names in the works of Tolkien as well. --Kjoonlee 13:56, 8 August 2006 (UTC)

I fear this thread is diverging rapidly--Light current 13:27, 8 August 2006 (UTC)

Sorry, firebrand was a bad googletranslatetool try. Let's say ember : hot burning wood. I meant that it is not the red that heats in it. -- DLL .. T 18:44, 8 August 2006 (UTC)
Ember is also a sort of bad translation. The sun's heat and light come from nuclear fusion, not combustion. Although it looks red, this is because the plasma is hot and acts as a blackbody, radiating energy in the visible spectrum and other wavelengths as well. You feel warm because you absorb some of the radiation in ALL wavelengths (albeit, more from some spectral elements than others). Ultra-violet radiation contributes to your tan (a bio-chemical process); infrared directly heats you, and visible light does contribute some heat as well. However, the sun is not an ember, or a firebrand - it is hot plasma of mostly hydrogen and helium undergoing thermonuclear reactions. Nimur 19:45, 8 August 2006 (UTC)

Ahh a sensible answer at last- THanks!--Light current 19:55, 8 August 2006 (UTC)

and not once did anyone mention seagulls

What the **"£$** have seagulls got to do with anything?--Light current 13:25, 9 August 2006 (UTC)

>> I thought the first two replies were sensible, and ansured your question, Not to make this thread any worse!--Aaron hart 07:24, 9 August 2006 (UTC)

Yes youre quite right Aaron. The first two replies were useful. Thanks 8-)--Light current 13:23, 9 August 2006 (UTC)


Moved to Wikipedia:Reference_desk/Misc

plz i am in ghana and did go to school but could not complete my highschool.but now i want to school in the nursing field at canada .so plz i will like to know how it will go and the steps i will be taking.i dont have any relations there but i want to school there and pursue my degree thank you

I think this question would have better chances on the 'Misc' page.--Light current 16:18, 7 August 2006 (UTC)

with spelling and grammar like that youre not going anywhere =P -PitchBlack

I could say that you meant to say "With spelling and grammar like that you're not going anywhere." but that would be unprofessional. Sum0 10:18, 9 August 2006 (UTC)
But correct! 8-)--Light current 13:27, 9 August 2006 (UTC)
lol! --Proficient 12:14, 10 August 2006 (UTC)

GPS precision[edit]

I know that GPS receivers usually report an estimate of the accuracy of the readings they provide, but I'm curious about their precision. Most give readings with seven digits, like N12° 34.567 W12° 34.567. How can you figure out the distance between that point and the very near one at say N12° 34.568 W12° 34.567? The distance between any two longitude lines is going to vary depending on how far you are from the equator, right? Is there any website that will calculate the distance between any two lat/long coordinates? 18:53, 7 August 2006 (UTC)

Use some version of the way you find the distance between two points on a Cartesian coordinate plane. I don't know how. — [Mac Davis] (talk)
A simple Google search on latitude distance came up with as the first entry. Skapur 20:09, 7 August 2006 (UTC)

The circumference of the Earth is about 40.000 km or 360x60 = 21600 minute. So 1' = 1.85 km. That goes for all lattitudes and for longitude at the equator (at least if Earth were a perfect sphere, which it isn't, but I'm only giving an estimate here). For any other longitude, you have to multiply by the cos of the (mean) longitude. Luckily, you save me that trouble because the longitudes are the same. And consequently, I don't need Pythagoras either (the square root of the sum of the squares of the two distances). So the answer to your example is 34.568 - 34.567 x 1.85 km = 1.85 m. As a rule of thumb, 1° latitude is about 100 km (actually 111 km) and the same goes for longitude at the equator. At 60° north or south (roughly Scotland and New South Wales) it's half that. DirkvdM 09:47, 8 August 2006 (UTC)

See the Great-circle distance article for details about calculating distances between points on a sphere along its surface. DMacks 19:48, 9 August 2006 (UTC)

Scientist famous for numbering all correspondence and papers[edit]

I remember hearing about some scientist, I believe he was a physicist, who numbered pretty much everything he wrote for several decades. From journal articles to letters to friends. The numbering scheme was his three initials followed by a number (I think it was 4 digits).

Can anyone remember his name for me? Thanks.

Doesn't everyone do that? Notinasnaid 19:46, 7 August 2006 (UTC)
A computer scientist who did that was Edsger Wybe Dijkstra. --LambiamTalk 02:12, 8 August 2006 (UTC)
If I did that here, 4 digits wouldn't suffice. DirkvdM 09:54, 8 August 2006 (UTC)
I think there's something there for all of us to think about, Dirk.  :--) JackofOz 12:03, 8 August 2006 (UTC)
It could do if the four digits were not decimal. hexa would'nt suffice ; but you may create any base (I have my eyes on the 'insert' template when editing this : 0123...ABC...ĕØΘЫɱ). -- DLL .. T 18:38, 8 August 2006 (UTC)

Death of fruits and vegetables[edit]

Usually I am able to answer my child's questions alone or by some quick research but this one has me stumped. My son asked me if the blueberries he was eating were dead. Are fruits dead when they are picked? When they rot? Some indeterminate time between these two? I appreciate anyone's help.

James [email removed]

I would personally not consider a fruit or vegetable to be completely dead until it is unable to be planted and grow into a plant. There's still a seed of life inside anything that can be planted and grow. (forgive the pun) And by this reckoning, fruit can live for a very long time.
I believe the cells of most fresh fruits and vegetables are alive. When they die, they rot. The fact that picked fruits can continue to ripen is evidence they are alive. Seeds remain alive even after the fruit that contained it has died. Cooking, canning, toasting, and freezing kill cells, so non-fresh fruits and vegetables are not alive. --Ginkgo100 talk · contribs · e@ 20:56, 7 August 2006 (UTC)
I think when we say that "X is alive", sometimes we mean "X is a living organism". As an example, we never say a person is alive after their heart and brain have permanently stopped working, no matter how many of their cells are still metabolising. So in this sense "alive" and "dead" have no meaning for picked fruit, because a fruit is not an organism. But other times when we say "X is alive" we mean something like "X is a collection of metabolising cells" or "X is a tissue or organ that could still function as part of an organism". So a fruit is alive the way a heart that's about to be transplanted into someone is alive, but not the way a person is alive. The seeds, of course, are alive in both senses. --Allen 21:51, 7 August 2006 (UTC)
There is a difference between plants and animals. In animals, the life of the organism is more important than the individual cells. By analogy, you could view the cells as bees, and the organism as the hive. The life of an individual bee is unimportant, only the hive matters. In plants, however, the individual cells and organs are more important than the organism, since they can survive and reproduce independently. (There are exceptions, like a planarian, which reproduces more like a plant.) So, I don't think you can apply the same rules to determining whether a plant, or portion of a plant, is dead that you apply to a human. I would say a piece of fruit is still alive, as long as it can still grow a new plant. StuRat 10:48, 8 August 2006 (UTC)
I love kids for asking such questions. That love quickly changes to hate when I try to answer them. One of the most important criteria for life is reproduction. Since fruit is itself a reproductive organ (?) it is alive as long as it can reproduce. Or is it the seed that is alive? If you remove it from the fruit, is the fruit then dead? Then again, I can still reproduce if I lose a leg, but that doesn't prove my leg is dead. Aaaarghhh! Also, I am now mixing up the definition of life in general (eg are viruses alive) and specific living things (eg is a headless chicken alive). DirkvdM 10:02, 8 August 2006 (UTC)
How can things live if they are cut off from their source of nutrients? Plucked Fruits have no source, so if they are not dead stright after plucking, they soon will be. THe question of rotting is something else, probbly depending on attack by fungi, bacteria etc. The seeds are not alive either-- only when supplied with nutrients can they grow and live.--Light current 12:01, 8 August 2006 (UTC)
Again, I think you are incorrectly applying animal standards for life and death to plants. The plant world has states between what we know of as life and death in the animal world (with perhaps a few exceptions, like spiders and insects that can stay dormant for years, then "come back to life" when conditions are right). I would say seeds are alive as long as they still possess the ability to sprout. StuRat 22:54, 9 August 2006 (UTC)
I am not eating now. Does that mean I am dead? DirkvdM 08:59, 9 August 2006 (UTC)
LOL. Probably, at least from the neck up! (joking) 8-)--Light current 13:51, 9 August 2006 (UTC)
See life--Light current 13:20, 8 August 2006 (UTC)
Once a fruit is picked, can it be reattached to the plant it was picked from and start growing again? If so then I have to say at the point where this can no longer be done is the point of death. Keep in mind people have severed fingers and had them reattached hours later. Also, it seems link the plant which grows the fruit is what is really 'alive' not the fruit itself.
I saw a headless chicken once (on TV). It would run around the farm yard bumping into things. It was kept 'alive' by its owner pushing corn down its severed neck. 8-(--Light current 14:15, 8 August 2006 (UTC)
Oh my mistake-- it was here Headless_chicken--Light current 14:35, 8 August 2006 (UTC)
Usually not, but after a fruit is picked it can often be planted and grow into a new tree/plant/bush.... TenOfAllTrades(talk) 14:45, 8 August 2006 (UTC)
Yeah but thats because you are providing some nutrition again. THe plucked fruit probaly survives a short time. what about cut flowers in water, are they alive - or just not dehydrated?--Light current 14:58, 8 August 2006 (UTC)
Once I saw a vegetarian eating a banana. I asked her how would she like it if her skin was ripped off and she was eaten alive. Heh. This is by Carl Sagan, regarding your love-hate relationship with children's questions.

In East Africa, in the records of the rocks dating back to about two million years ago, you can find a sequence of worked tools that our ancestors designed and executed. Their lives depending on making and using these tools. This was, or course, Early Stone Age technology. Over time, specially fashioned stones were used for stabbing, chipping, flaking, cutting, carving. Although there are many ways of making stone tools, what is remarkable is that in a given site for enormous periods of time the tools were made in the same way—which means that there must have been educational institutions hundreds of thousands of years ago, even if it was mainly an apprenticeship system. While it's easy to exaggerate the similarities, it's also easy to imagine the equivalent of professors and students in loincloths, laboratory courses, examinations, failing grades, graduation ceremonies, and post graduate education.

When the training is unchanged for immense periods of time, traditions are passed on intact to the next generation. But when what needs to be learned changes quickly, especially in the course of a single generation, it becomes much harder to know what to teach and how to teach it. Then students complain about relevance; respect for their elders diminishes. Teachers despair at how educational standards have deteriorated, and how lackadaisical students have become. In a world in transition, students and teachers bother need to teach themselves one essential skill—learning how to learn.

Except for children (who don't know enough not to ask the important questions), few of us spend much time wondering why Nature is the way it is; where the Cosmos came from, or whether it was always here; if time with one day flow backward, and effects precede causes; or whether there are ultimate limits to what humans can known. There are even children, and I have met some of them, who want to know what a black hole looks like; what is the smallest piece of matter; why we remember the past and not the future; and why there is a Universe.

Every now and then, I'm lucky enough to teach a kindergarten or first-grade class. Many of these children are natural born scientists—although heavy on the wonder side, and light on skepticism. They're curious, intellectually vigorous. Provocative and insightful questions bubble out of them. They exhibit enormous enthusiasm. I'm asked follow-up questions. They've never heard of the notion of "a dumb question."

When I talk to high school seniors however, I find something different. They memorize facts. By and large, though, the joy of discovery, the life behind those facts, has gone out of them. They're worried about asking "dumb questions;" they're willing to accept inadequate answers; they don't pose follow-up questions; the room is awash with sidelong glances to judge, second-by-second, the approval of their peers. They come to class with their questions written out on a pieces of paper, which they surreptitiously examine, waiting their turn, and a oblivious of whatever discussion their peers are at this moment engaged in.

Something has happened between first and twelfth grade, and not just puberty. I'd guess it's partly peer pressure not to excel (except in athletics); partly that the society teaches short-term gratification; partly the impression that science or mathematics won't buy you a sports car; partly that there is so little expected of students; and partly that there are few rewards or role models for intelligent discussion of science and technology—or even for learning for its own sake. Those few who remain interested are vilified as "nerd," "geeks," or "grinds."

I also find many adults are put off when young children pose scientific questions. It is critical that this cannot happen. Why is the Moon round? Why is the grass green? What is a dream? How deep can you dig a hole? When is the world's birthday?" Too often, many teachers and parents answer with irritation or ridicule, or quickly move onto something else: "What did you expect the Moon to be, a square??" Children soon recognize that somehow this question annoys the grown-ups. A few more experiences alike, and the child is lost to science. Why should adults pretend omniscience before 6-year olds, I am baffled. What is wrong with admitting we don't know something? Is our self-esteem that fragile?
— Carl Sagan, The Demon-Haunted World: Science as a Candle in the Dark

[Mac Davis] (talk)

Agreed. --Proficient 12:17, 10 August 2006 (UTC)