Wikipedia:Reference desk/Archives/Science/2010 January 23

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January 23

Avalanche season in the Canadian Rockies

Could someone tell me what time of year are avalanches likely to happen in the Rocky Mountains in Alberta (in the vicinity of Jasper / Dawson Creek)? Also what months are the worst in terms of avalanche severity? Thanks in advance! 24.23.197.43 (talk) 03:30, 23 January 2010 (UTC)

I'm not familiar with the areas, but I'd recommend asking people who are before venturing into those areas if you have any doubts. Falconus^{p t c} 05:05, 23 January 2010 (UTC)

Well, late winter/early spring would be the worst, since avalanches are most likely when the snow and ice starts to melt and the weight goes out of balance on the slopes. At that point, there is so much snow, the slightest trigger would let the mountains come tumbling down. That being said, there is always a risk of avalanches so long as there is snow.

That said, there is no risk of avalanche in Dawson Creek (which is in BC, not Alberta) because Dawson Creek is flat and about 7 hours away from Jasper. Aaronite (talk) 06:45, 23 January 2010 (UTC)

Thanks for the info, you really helped me out on this. Now, what's the latest in the springtime that avalanches are likely to occur in the Jasper area? I'm writing a series of action-adventure novels about rescue pilots, and I need to know how late in the spring I can set the second one, or whether I should move up the first one by a few weeks. Clear skies to you! 24.23.197.43 (talk) 07:42, 23 January 2010 (UTC)

Hudson Bay ice

What months is the northern part of Hudson Bay (around Baffin and Southampton Islands) frozen over? Also, how thick does the ice get in that part of the bay? Thanks in advance! 24.23.197.43 (talk) 03:34, 23 January 2010 (UTC)

There is some general information about ice in the linked article. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:37, 23 January 2010 (UTC)

Just took a look at the article, it says that the bay can stay frozen as late as mid-June but the ice breaks up in the northern part first and then in the south. Thanks, and clear skies to you! 24.23.197.43 (talk) 06:20, 23 January 2010 (UTC)

These things usually differs from year to year. Some years, it's colder than usual and thus more ice, other years may be warmer than usual and with less ice. Depending on what month is coldest a particular winter, the answer can differ. E.G. (talk) 01:08, 24 January 2010 (UTC)

Here is a map showing current sea ice extent in the Northern Hemisphere, including Hudson Bay. ~AH1^(TCU) 19:41, 25 January 2010 (UTC)

Wow, the map shows that everything is frozen over! That's no big surprise this time of year, is it? Clear skies 146.74.230.82 (talk) 00:57, 26 January 2010 (UTC)

Help explain "bandwidth" in wired connections

I wasn't sure to post this in Science or Computing. But since I wanted more of an EE sciencey explanation, I'm posting here. I'm having a little trouble with the concept of bandwidth concerning video and/or computer cables. For example, why a Cat5 cable cannot carry 10 gigabit signals, or why an audio cable with BNC connectors can't transmit Serial Digital Interface signals. Physically, cat5 looks the same as Cat6, and a BNC audio cable looks exactly like an SDI cable. And it's just pulses of electricity right? Help me out. --68.103.143.23 (talk) 05:27, 23 January 2010 (UTC)

Um, did you read the articles you linked to? E.g. Although it is sometimes made with 23 AWG wire, the increase in performance with Cat-6 comes mainly from better insulation; 22 to 24 AWG copper is allowed so long as the ANSI/TIA-568-B.2-1 performance specifications are met" Interference including crosstalk and alien crosstalk are of course big issues with ethernet cables and the reason balanced lines are used (again as mentioned in our articles). Ethernet physical layer, Ethernet over twisted pair & 10 Gigabit Ethernet may also be of interest. Note that cat 5e (but not cat 5) can carry 10GE albeit the range being limited to 45m Nil Einne (talk) 05:31, 23 January 2010 (UTC)

As the articles at Wikipedia note, Bandwidth (computing) is more closer related to Throughput which is the term for amount of data one can cram down a wire. The concept seems quite different from Bandwidth (signal processing), which refers to the part of the radio spectrum ('band') occupied by a particular wireless signal, i.e. literally the "width" of the "band" occupied by the wireless data signal. Using the term for wired communication seems a bit "weird" until one reads the articles, and realize that the throughput of a digital system is related to the freqency of the analog signal carrying it, via Hartley's law. Thus, digital throughput is related to analog bandwidth, and they really are connected concepts. I'm by no means an expert on this stuff, but it is explained in the articles. --Jayron32 05:50, 23 January 2010 (UTC)

Bandwidth in computing is directly related to bandwidth in analog signal processing. Insofar as an analog physical layer is always present, even in digital communication, the channel capacity is limited by the frequency bandwidth that the cable connection can sustain. That band depends on, among other things, the circuit design of the amplifiers and signal conditioners at each end of the wire; and the inherent physical and electrical properties of the wire. (See distributed element model or transmission line for some elementary physics overview). A digital signal does occupy a width of a frequency band - usually in the radio frequency range of the electromagnetic spectrum - even if the signal is contained within a wire. This is because the data is digitally modulated on to a carrier (which may or may not be baseband, depending on the technology in use). Jayron's links are the best place to get started with these concepts. In actuality, there's nothing weird about transmitting radio by copper wire - it's a better medium than air, in a lot of respects for communication purposes. Nimur (talk) 07:08, 23 January 2010 (UTC)

Well, yes, its just that in computing "Bandwidth" is often used to mean "How many bits of data can I cram down this wire", which sounds more like "throughput", and at first glance sounds like it is unrelated to the radio wave frequency bands. I provided the above links to show the physical connection between the two concepts. --Jayron32 16:02, 23 January 2010 (UTC)

Best long-term energy storage?

Would someone able to read [1] and/or [2] please tell us what they say is the most economical long-term energy storage system? 99.25.112.22 (talk) 06:02, 23 January 2010 (UTC)

If you want to know for the energy storage article, Wikipedia:WikiProject Resource Exchange is the better bet if the problem is access rather then understanding. If the problem is understanding, I wonder whether trying the talk page first may be the better bet. Nil Einne (talk) 06:09, 23 January 2010 (UTC)

This sounds interesting, but unfortunately I can't access either article cause I'm not subscribed to the journal. Could you tell me in your own words what's being compared to what? Clear skies 24.23.197.43 (talk) 06:25, 23 January 2010 (UTC)

Neither paper makes a concluding remark about the most economic long-term storage solution. The first paper is a literature review on research into various materials that have been used for latent heat storage (e.g. just heating up a material). Its conclusions are that all prior research is near-impossible to compare, because of a lack of standardized measurements. They identify phase-changes of various waxes and other materials as a possible energy storage scheme, but make no clear, concise remarks on feasibility or economy of such a method. The second paper is a review of thermochemical sorption as an additional way of storing heat (sort of a chemical analog to a physical phase change, allowing some control of reaction energetics). The author summarizes the conclusions of prior studies: that chemical heat pumps are consistently the only feasible option for short term storage (because well-suited chemical storage materials don't exist).

It's my opinion, independent of my reading of these papers, that long-term thermal energy storage is uneconomical for the simple reason that heat radiates. I would suggest that alternative storage methods, like electric or chemical batteries, are the most economic storage scheme - until we find a way to economically synthesize long-chain hydrocarbons using electricity and CO2. Unfortunately, none of these solutions are actually very economic - even if ideal processes actually existed, the cost of producing new energy is presently too low to make storing "old" energy worthwhile. If you're willing to consider the reservoir behind a hydroelectric dam as a long-term energy storage mechanism, then that probably qualifies as the single best economic region-scale method of storing energy. (My back-of-envelope calculations estimate that 1 cm of rain stores 11,500 gigajoules of extractable energy in Lake Mead). Try storing that with thermal latent heat systems! Unfortunately, it's not very feasible to store this in hydrological gravitational potential energy - unless you already have a reservoir somewhere, and a source of lower water you could pump to fill it. Finally, I'd just say that energy storage is unnecessary if you switch to energy generation methods that can easily scale according to demand curves - such as nuclear-electric and hydroelectric plants. Nuclear power plants can use control rods to ramp up and down the amount of energy in the reactor. Hydro plants can control the flow of water with flow gates, ranging from zero to full-blast, to ramp production. In combination, these schemes would render energy storage moot - you could build infrastructure to meet your maximal demand, and when that is unneeded, no energy would be wasted. Coal plants, as a counter-example, cannot easily "throttle back," because they have a very narrow regime of operation (coal has to be shoveled in at roughly the same rate, while nuclear rods can be highly throttled). Solar, wind, and other energy production schemes are totally uncontrollable - you get as much power as the sun is willing to shine and the wind is willing to blow. Nimur (talk) 07:22, 23 January 2010 (UTC)

I agree 100% with Nimur, but would add that tidal hydroelectric generation could be combined with super-efficient storage by pumping water up when excess energy is available at high tide and using the extra height gain to obtain more energy back at low tide. (The process actually gives back more energy than is stored, even though the pumps and generators are less than 100% efficient, because extra energy comes from the rotation of the earth-moon system.) The varying lag in time of high tide round the coast of the UK could give continuous generation, though less energy would be available during the week of neap tides at first and third moon quarters. Dbfirs 12:40, 23 January 2010 (UTC)

Energy production is not a zero-sum game. If you build excess wind capacity, you can achieve any level of reliability you need. It increases costs, but less than flood insurance would otherwise increase them as long as you're displacing carbon. 99.38.150.198 (talk) 14:16, 23 January 2010 (UTC)

The best long term energy storage is achieved by tapping into naturally-available wells of it, like petroleum, or solar energy. If you are thinking of sitting down in a bunker waiting for the Apocalypse to come, you may be waiting a rather long time. Vranak (talk) 13:04, 23 January 2010 (UTC)

I am not waiting for the apocalypse, and I believe wind power (a form of solar) with grid load balancing such as http://ice-energy.com would negate the need for any of the traditional "reliable" baseline sources, except perhaps 20% hydroelectric, especially if it were upgraded to pumped storage hydroelectricity. 99.38.150.198 (talk) 14:16, 23 January 2010 (UTC)

Unfortunately, your belief is counter to expert opinion. For a succinct summary, take a look at Forecasts and Analysis of Energy Data from the United States Department of Energy. Even a very optimistic outlook and rapid growth of wind sector puts it at a miniscule (I would even go so far as to call it trivial and negligible) fraction of the total energy production. I think you will be hard-pressed to find any well-thought-out energy solution which uses wind energy without a baseline production scheme. Nimur (talk) 19:01, 23 January 2010 (UTC)

By "miniscule" do you mean "fastest growing?" 99.38.150.198 (talk) 03:31, 24 January 2010 (UTC)

By "miniscule" I mean that even if wind energy grows extremely fast, meeting optimistic, exponential growth curves, the Department of Energy speculates that it will be less than 5% of total electricity production capacity and supply less than 2% of total energy consumed in the United States by 2030. Data from the Energy Information Agency, supplementing the 2010 Energy Outlook report. Nimur (talk) 06:55, 24 January 2010 (UTC)

Why is there an inflection point at about year 2013 on page 21 of http://www.eia.doe.gov/neic/speeches/newell121409.pdf -- what reasons are there to believe that wind growth will suddenly slow so dramatically? 76.254.71.123 (talk) 01:10, 25 January 2010 (UTC)

That halted growth projection might be a cynical outlook on prospects for continued federal support for renewable energy. But more seriously, this 1995 report explains that most wind projects have been integrated into the grid not because they are cost-effective, but because of government programs: "In many cases, the planned projects were not selected because of their economic competitiveness, but were initiated because State governments or Public Utility Commissions provided additional incentives..." As the weak economy dries up these government incentive programs, a realistic outlook is that the more expensive alternative energy sectors will become more and more marginalized. Let me again point out the fallacy of scalability - if everybody adopted a more expensive energy solution, no macro-market would exist to subsidize it. Wind power would thus need to stand its own ground on economic merits - which it cannot do, given realistic projected energy prices over the next few decades. Here's another good resource - Wind statistics. That ever-elusive geographic intersection between land that is good for wind electric production and land that is near a place with high electric demand and finally, most importantly, land which is legally owned by somebody (state or Federal government) who can use it for power production is rapidly saturating. This overview map, map 2, and these data tables, indicate that the best sites have already been developed. What's left - we can build wind power production facilities in places where they aren't needed, but that's very uneconomic. I suspect that a combination of these factors is responsible for the 2013-ish tail-off in wind electric growth. Nimur (talk) 01:56, 25 January 2010 (UTC)

Do you really think that the Department of Energy includes political considerations in staff projections? Honestly, that could explain it, because the other explanations are all implausible. The 1995 EIA report is very much at odds with the actual experience of, e.g., Colorado, where officials call 30% renewables by 2020 possible "with or without legislation."[3] Moreover, your colleagues at Stanford and U.C. Davis have widely published a plan to reach 100% renewables world-wide by 2030 using only a subsidy scheme paid for by reduced flood costs.[4] Is there any evidence from the past five years that wind has reached anything approaching saturation? 76.254.71.123 (talk) 22:31, 25 January 2010 (UTC)

I'll tell you the same thing I tell my colleagues at Stanford and U.C. Davis. If wind energy is the wave of the future, and is so economically viable, why don't you start investing heavily in it? The usual response is a series of dumb looks - experts in wind energy don't drink their own kool-aid and don't believe blogs that claim wind will power the entire country in two decades. They also commute to work in petroleum-powered automobiles when it's inconvenient to bike. But I fear we may be far off topic by now. Maybe we can continue this discussion elsewhere. Nimur (talk) 13:51, 26 January 2010 (UTC)

After reviewing your link, which should be www.ice-energy.com, I have to do some bubble-bursting. This is not an energy-storage solution. It's not even energy-efficient! What these devices are, are commercial/industrial size air conditioners that they are selling to residential customers. The plan, if I may boil it down, is to be less energy efficient by over-cooling the AC unit during the night (when electricity is cheaper). This means that lots of refrigerant is sitting around in the unit, cold, doing nothing (and slowly warming back up). Then, although this is wasteful, they trickle the coolant into the unit for the duration of the day, when the users want to turn the AC on. They are actually using more energy for the same amount of cooling, because of inefficiency in the thermal storage (by thermal radiation, as I mentioned above). However, this scheme will ironically actually cost less, because energy is cheaper at nighttime in some markets. The plan, as it stands, is to increase demand for electricity at night - not to decrease total demand for energy.

The enthusiastic respondant will reply, "but if everyone switched to these systems, the energy demand during the daytime would be lower!" But, this is nonsense. If everybody switched to these systems, energy demand would be high at nighttime, and it would no longer be economic to charge a different rate per kilowatt hour at night. And since the inherent thermodynamics are not in favor of energy storage, more total energy would be consumed. These schemes only work as an economic way to save costs if a very few people use them. Essentially, they are playing off the market price curves of the aggregate economic system by participating as "non-ideal" consumers - they are a niche market. If that market grew to large scale, it would be subject to the same commodity pricing as we have now.

I am baffled how many of these plans I see as proposed solutions to the energy challenges our society faces. They're only one notch above the ill-conceived perpetual motion machine - and they also indicate that our schools do a bad job teaching thermodynamics. Storing energy results in losses. This is a fundamental result of thermodynamics. Therefore, any energy storage mechanism will actually increase total energy demand, compared to an equivalent system which only draws as much power as it needs currently, i.e., if the power plant can scale its production. If the plan is to transform our entire society to use an energy storage system, whether it is city-wide or locally distributed on rooftops, then we will consequently increase our total societal energy consumption, because there is waste in every energy storage scheme. Nimur (talk) 19:17, 23 January 2010 (UTC)

Tidal pumping is the one exception to any energy storage mechanism will actually increase total energy demand, but I agree that there are problems with growth of marine organisms in such systems. Perhaps the only long-term, eco-friendly, complete solution to energy needs is nuclear fusion, but this is far in the future unless a vast amount of money gets thrown at the development. Meanwhile nuclear fission will probably have to be used much more extensively to reduce global warming, with safe disposal of waste products of course. Dbfirs 20:49, 23 January 2010 (UTC)

Nimur, I'm pretty sure the anonymous poster understood all that. The idea is not to convert everybody, but to convert enough people that nighttime and daytime energy demands are roughly equal; then you can reduce your peak capacity, which might yield savings that exceed the storage losses. Or it might not; I couldn't tell you. But it's not an inherently illogical idea. -- BenRG (talk) 00:48, 27 January 2010 (UTC)

I haven't read the link, but it seems to me converting everone is not necessarily going to result in there being a lot higher night time usage then day time. It depends on various factors particularly how much of the energy usage is due to AC. From Nimur's description, you will only be moving the AC usage to be increased during the night time (and hopefully decreased during the day time), there are still clearly plenty of other things which will be used during both times and some of them may be higher at day time. For example many shops, offices and factories operate primarily during the day time and while AC will be part of what contributes to their energy usage it's not the only thing. Also given the OPs comment, perhaps one of the ideas is for a more dynamic smart usage system where the AC is turned on and off depending on the availability of energy and stores it when it's high, to be used when it's need. I'm not saying I think it's a good idea or will work. Actually from Nimur's description it sounds silly. Nil Einne (talk) 12:33, 27 January 2010 (UTC)

oxygen's diradical nature ... what about the halogens?

Oxygen's diradical nature supposedly stops its radical nature from oxidising all organic compounds at room temperature, except for the trace singlet oxygen that occasionally forms. Yet, chlorine and fluorine, etc. are not diradicals, yet they are dangerous oxidants at room temperature. Aren't a great deal of their oxidative properties non-radical in nature? Or is it because *O- (radical anion) makes a bad leaving group, as opposed to Cl-? (But F- isn't a great leaving group either...) John Riemann Soong (talk) 09:47, 23 January 2010 (UTC)

I think you are crossing wires on two sometimes slightly related concepts. Radicals can be good oxidants, but a) not all radicals are always good oxidants (consider the dozens of odd-electron metals) and b) there are lots of good oxidants which have no radical nature (say, permanganate. What makes something a good oxidant or not is much more closely related to the electron affinity of the species, rather than the odd/even nature of its electrons. Even though dioxygen has two "unpaired electrons", as predicted by molecular orbital theory, that actually gives those two electrons the opportunity to spin couple; which is actually somewhat slightly MORE stable than opposite-spin pairing. This is what gives stability to the electron configuration displayed in chromium, the s1d5 configuration rather than the s2d4 configuration. --Jayron32 15:57, 23 January 2010 (UTC)

Over-watering my Philodendron

I've got a Philodendron that much to my chagrin I seem to have over-watered: the leaves are yellowed, soft, and wilting. I understand the concept of over-watering in general - the roots begin to rot, not enough oxygen, etc. But this very plant began as a collection of cuttings sitting in a glass pitcher filled solely with water not 6 months ago. The roots developed and then I transferred it to a soil pot where it was growing fine enough until just recently. This is fascinating. Could someone please explain to me how a plant that grows perfectly well in 100% water can receive too much water when it's in soil (and quantitatively receiving less)..? 61.189.63.173 (talk) 10:06, 23 January 2010 (UTC)

When there are a few roots in water there is enough oxygen, but with many roots and organic matter and bacteria in soil there are heaps of things using oxygen, and it is all used up. Graeme Bartlett (talk) 21:49, 23 January 2010 (UTC)

I and other people find it a problem to decide when a pot plant needs watering. Purpose-made probes that suppossedly measure the soil dampness do not work. I've concluded that the way to do it is by weight - when the pot+earth feels light, water it. Pot plants seem to do better by fluctuating in the moisture of the soil rather than trying to keep them moist all the time - reflecting what happens in nature I suppose. 92.29.81.16 (talk) 11:23, 24 January 2010 (UTC)

Different plants have different preferences though. If you use the same pattern or watering with a variety of plants, you will find which ones will survive by artificial selection. Philodendron did not survive with my watering practice - once a week, but may have been to do with environment too. Light, temperature and humidity can be important too. Graeme Bartlett (talk) 00:19, 26 January 2010 (UTC)

Circulation in Whitefish

Most of my life (decades!) I have wanted to know how the flesh of whitefish remains white, even though their blood is red. How does the red blood supply the white muscle without the capillaries making that flesh look some shade of red or pink?

I have tried the following Google searches: "whitefish muscle" and "whitefish circulation".

Budgie Helen (talk) 12:14, 23 January 2010 (UTC)

Meat (of fish or fowl or other animal) is white or red based on the content of myoglobin, a muscle protein, not on the basis of the color of the animal's blood. See [5] and [6] for further detail. - Nunh-huh 12:35, 23 January 2010 (UTC)

Relative levels of myoglobin are what define "white meat" and "dark meat." As indicated to some extent in White_meat#Poultry and Muscle#Types, type I muscle is slow twitch and capable of sustained activity. It is often termed red and in chickens, for example, which do not do a lot of flying, this type exists in the legs, which perform the bulk of the bird's activities. Breast meat in chickens is white because it's primarily type II muscle, which is fast twitch and incapable of sustained activity. In ducks, which are built for a lot more upper body activity, there is really no white meat, and both uppers and lowers are red. DRosenbach ^{(Talk | Contribs)} 13:51, 26 January 2010 (UTC)

hot water storage

electric hot water tank

There is no "handyman" ref desk, so I'm going to pester the scientific folk with my inanity. I have a question regarding the pipe (and associated valve) on the bottom of my hot water tank (see visual aid). When I first moved in to the flat (at Christmas), the valve was in the "off position" and a friend (perhaps as dim as me) remarked that it may be a waste pipe and should be "open", and twisted it (seemingly forever) to the right left. I suspect that it's "cold water in", actually. All the way to the right left, it leaks water out of the top of the valve, though not very much. Too much pressure? Even about halfway to off there seems to be some slight discharge. How far away from off should the valve be? How much water is the ideal amount to let in (if it is the cold water in as I suspect) and how do I know when I've achieved this? Is there any danger or unwanted side effect to leaving it completely open with the slight leak? I find that I run out of hot water very quickly (not enough for a shower and the washing up in the same day), is there any chance it's because of this valve (or is it just because the tank is super tiny for my extortionately long showers)? Advice, guidance, knowledge, sneering, and sympathy all welcome. Thank you! Maedin\^talk 13:12, 23 January 2010 (UTC)

Have you had a look on the blue label that appears prominently on that tank? 93.132.166.231 (talk) 13:43, 23 January 2010 (UTC)

If you have a look at the diagram (as IP 93 suggests) on the heater it says that the pipe with the valve is the cold in!.:-) If there is a waste or overflow pipe I hazard a guess it may be behind the heater, possibly leading outside or connected to a drain pipe. This is installed under a kitchen counter or similar apparently? The label at the bottom says 125 L (Litres I expect). Does not seem very large, I suggest shorter(!) or cooler(!!) showers; or showering and 'washing up' (clothes?) on seperate days(!!!). I can't say too much for certain about how far the valve should be opened, if your local water pressure is 'high' then it is theoretically possible it could stress the pipes/connections. Perhaps turn it off to 3/4 and if there is no problem turn it down a bit more? Too far and your heater may shut off entirely.(or burn out if not enought water to cover the elements.) You say 'flat', if this is a rental then the landlord may be able to help? 220.101.28.25 (talk) 13:50, 23 January 2010 (UTC)

(e/c with Dbfirs below) I did say sneering is welcome, so I'll just say that yes, of course I noticed the blue label, and no, it doesn't really answer my questions, does it? You'll notice that I didn't actually ask, "is this the cold water in?" If I hadn't read the blue label, then I probably would have believed the person who claimed it was a waste pipe. I am (as you may have noticed^^) female and either don't believe labels that come on hot water tanks or assume that I am misunderstanding them, and the friend who made the initial guess was male (and I was reluctant to admit that a guy might not know what he was talking about regarding these things). "Washing up" is the British term for "doing the dishes", btw. Yes, I'm renting the flat, but landlords are notoriously tardy at responding to non-urgent queries and mine has been no different. Thanks for your help so far, :-) Maedin\^talk 14:08, 23 January 2010 (UTC)

Just open it sufficiently for your shower to operate at a reasonable flow. Closing this valve more will reduce the flow and increase your warm shower time. I was puzzled when you said turning to the right to open because most people would think you meant clockwise looking from above, and that would close the valve. Dbfirs 14:03, 23 January 2010 (UTC)

I did mean left, thanks, :-). Maedin\^talk 14:16, 23 January 2010 (UTC)

Here is the manual: http://www.ariston.co.uk/uploads/doc48ad4c024f798.pdf 93.132.166.231 (talk) 14:33, 23 January 2010 (UTC)

It's not really about "too much pressure". As you turn the spindle to open the valve, you'll notice that the amount of spindle (The spindle is the round shaft that is attached to the handle, and disappears into the body of the valve) you can see sticking out the top of the valve increases (this is because there is a screwthread cut into it further down inside the valve and, as you open the valve, this unscrews - it's what actually makes the valve work).

The next thing you need to know is that there is a seal (called the gland) around the spindle. It is just underneath that odd-looking nut (sometimes called a gland follower) that fits round the spindle where it goes into the valve body.

What is probably happening is that as you open the valve fully, the bit of the spindle in contact with the gland changes (as the spindle moves out, you try to seal on a bit that's lower down) and you've probably hit a patch that's a bit rough or dirty.

To start with, try tightening the gland follower a little bit. One or two flats is usually sufficient (a flat is one sixth of a turn - as soon as you look at it, you'll appreciate why) - but your aim is to get a decent seal without making the valve too stiff to turn. If that doesn't work, you may need to repair the gland. That needs a bit more care as, if you get it wrong, you could cause a significant flood.

In terms of how far to open the valve, standard practice is to open it fully (assuming you have eliminated your gland leak), and then close it a quarter turn (to stop the threads binding). Zeusfaber (talk) 18:18, 23 January 2010 (UTC)

As a rule of thumb - a shower uses 2 US gallons of water per minute. If you read the label right and the tank contains 125 liters then that's 33 US gallons - and should be enough for a 16 minute shower. Of course if the water is really hot - you're probably mixing it about 50/50 with cold water - so I'd guess that you could sit in the shower for half an hour without running out! You should probably be aware of the amount of hot water that other activities uses: Taking a bath can use 50 gallons - and if more than half of that is hot water from the tank - then you could easily run out. If your clothes washer uses hot water, then it'll take 10 gallons (but with modern detergents, you can save a ton of money by doing cold water washes) - and if your dishwasher is plumbed into the hot water lines then it can take 20 gallons. SteveBaker (talk) 18:51, 23 January 2010 (UTC)

Doesn't the tank begin refilling itself before it hits rock bottom empty? If it's re-filling itself with cold water you won't get the full 32 minutes of hot shower. APL (talk) 03:31, 24 January 2010 (UTC)

Yes, the tank starts filling with cold water as soon as the shower is turned on. It relies on the layering effect (hot water being less dense than cold) and lack of turbulence. By the time half the hot water has been used, a temperature drop will be noticeable, but the top half will still be much hotter than the cold water in the bottom half. Dbfirs 08:11, 24 January 2010 (UTC)

[Unindent]. Let's start by describing your tank. There are 3 copper pipes connected to it, which are all water connections. The one at the bottom is the cold water in. The next one up is the hot water out. The one slightly higher than that (with the black plastic valve on) is a pressure relief. The first 2 do what you'd expect - let cold water in and hot water out to your shower, etc. The other one takes care of the chance that your cold water pressure might just possibly be high enough to damage the tank. If it is, the black valve will release to let water out and to safeguard the tank. In all normal circumstances it will not operate ever. The pipe at the bottom has the valve that you're worrying about on it - this is a stop cock and is essentially just used to turn the cold water on and off - it's not really designed to be left partly open or closed. I would advise turning it anti-clockwise (from the top) until it won't turn any more. Taps of these sort do have a tendency to leak when not fully open or closed, so this may well help your problem with the leak.

The cyclinder has 2 electrical heater ("immersion heaters") to warm the water up - these are the white things sticking out on the right. There are 2 since this is designed to work with Economy 7 - the lower one can be used at night to heat a load of water on a cheap tariff and the upper one is used at day to top the water up on a more expensive tariff. If you don't have Economy 7, you would just connect both to the electrical supply (this would have to be done by an electrician. Both of these have thermostats to set the temperature to which they heat the water. They should both be set to 60-65°C. I would guess that if you've not got enough hot water, it may simply be that the lower one is not connected, or set at too low a temperature.

By the way - the tank doesn't heat the water as you use it (much) - it pre-heats the water, which you then draw off. It looks like it's not insulated, so (a) you could almost certainly see how much hot water is in it by feeling the tank with your hand and (b) you are wasting money by letting the tank cool too quickly. You should ask your landlord to insulate it.

HTH. --Phil Holmes (talk) 10:41, 24 January 2010 (UTC)

You guys are great, thank you so much. I just have a few more questions, mostly in response to Phil.

I am not certain if I'm on Economy 7 or not, but I'm guessing so. I've got two boxes for mains switches; one box is labelled water heater and storage heater (yes, I heat this place with bricks, if you can call that heating^^) and the other is for . . . everything else. I assume I'm right in thinking that they wouldn't be separated if they weren't on different tariffs. This would explain why a shower in the morning means I have no hot water in the evening: it's not heating up any water except at night. How does that information change your advice? It seems to me that I need something topping up the temperature on a more expensive tariff; does that mean I need an electrician to connect the top immersion heater? Is this something I should be asking my landlord to take care of, or the sort of thing I should arrange myself? (If that seems like a stupid question, I've never been a tenant before, I owned before this (with a male of the species, hence my profound ignorance of water heating).)

The other thing is that the tank isn't warm. Not even a bit. So it must be insulated inside? A friend has helpfully suggested that I could take the cover off the tank and find out, but I'm not sure I have enough testosterone for such a crazy idea.

As suggested, I've now opened the valve fully and quarter-turned it back so the threads don't bind (whatever that means). The leak is really slight and I don't have the right tool for adjusting the gland follower, so I'll leave it.

Again, thank you!! Maedin\^talk 11:51, 25 January 2010 (UTC)

Yes it does sound like Economy 7 tariff. The tank is probably a modern one that is actually much smaller inside but has insulation built in. If there are two separate immersion heaters then the second one can be wired up to a switch so that you can boost the hot water whenever you wish (at the higher rate, of course). Has this not been done already? If not then you do need an electrician. Strictly, you also need your landlord's permission (and your landlord ought to pay for the work to be done!) If you are not able to ask your landlord, then a friendly electrician might be able make a temporary connection to a 13A plug, but this would be frowned on by Health & Safety experts because the tank is not a portable appliance. If you need lots of hot water for very long showers, it is actually possible to wire both immersion heaters to switches so that you can almost heat the water as you use it (5Kw is not quite enough for an instant shower unless the water is already warmish). A good electrician could wire this so that you still retain the benefit of Economy 7 rate overnight, but it is not standard wiring, so you would need someone who really knows what they are doing. Dbfirs 16:17, 25 January 2010 (UTC)

The real test of whether you have Economy 7 is the electricity meter - if there are 2 sets of dials on it then it's highly likely - have a look at the photo in the article I linked to and you'll see what I mean - one is labelled "Normal" (daytime tariff) and the other "Low" (night-time tariff). You could also see what it says on your bill. There must be a time switch (or more likely, two time switches) somewhere that control the immersion heaters turning on and off. If you can find them and can work out how to over-ride them (i.e. nothing worse than turn them on when they're already off owing to the time) then you could consider turning the lower heater on about an hour before you need a shower. But don't blame me when your electricity bill doubles! And I think I was wrong about insulation - another look at the manual and it dos look if there is some insulation built in to the tank. More is always better, though. --Phil Holmes (talk) 17:05, 25 January 2010 (UTC)

Hi, I am pretty sure that your upper heating element has burnt out. They often do if they are set to run too hot. It is only a small task so it should be easy to (get the landlord to) replace it. It is only four screws, one on the cover and three cables - live neutral and earth. Good luck. :-) Chienlit (talk) 19:31, 25 January 2010 (UTC)

Actually, they normally use an immersion heater spanner to screw them in and out, and that can take considerable force. It would also have been sensible to suggest draining the tank before trying this, to avoid flooding the place as all the cold water rushes out of the hole previously occupied by the heater. --Phil Holmes (talk) 12:16, 27 January 2010 (UTC)

why no hair in biodegradable waste?

The Dutch version of the article Biodegradable waste says that, in general, dog or cat hair is not considered biodegradable waste ("GFT") and should be treated as "regular" waste. Why is this? Is hair not biodegradable or compostable?

And what about human hair?

Thank you in advance. 83.81.42.44 (talk) 16:22, 23 January 2010 (UTC)

It depends on what they're going to do with the waste stream. If they're going to feed it to pigs, clearly you don't want pigs eating (too much) hair. If it's going to compost, it is biodegradable, but much more slowly (and I think in wetter conditions) than other wastes - so it'd still be hair when the rest of the stuff was ready to be used. If they're going to dry it use it to power an incinerator then hair is fine. -- Finlay McWalter • Talk 16:32, 23 January 2010 (UTC)

Hair is basically 'dead', and from the fact that it can still be found (ie on Egyptian Mummys) long after soft tissues are gone, suggest that it is not biodegradeable in any meaningful way. --220.101.28.25 (talk) 17:12, 23 January 2010 (UTC)

That's totally untrue. Mummies are preserved and dried and kept underground in a sealed container in a nearly lifeless environment. In normal conditions hair is decomposed by moths, fungi, and bacteria (ref (warning: a bit grisly)). If hair wasn't biodegradable then the world would be covered in a layer of meters of compressed hair. Being "basically dead" does not grant immunity from decay. -- Finlay McWalter • Talk 18:01, 23 January 2010 (UTC)

This says that at least one species of cockroach will eat hair and even fingernail clippings...so yes - it's definitely biodegradable. However, it may well not be compostable or recyclable in any useful manner - which would explain the comment in the article. SteveBaker (talk) 18:39, 23 January 2010 (UTC)

If it's only in the Dutch version, maybe it has something to do with [nl:Coffeeshop]s and cockroaches not meant to get chilled to much? 93.132.166.231 (talk) 19:54, 23 January 2010 (UTC)

What is energy?

I am currently taking an A-Level physics course, and I am very quickly falling behind my classmates, largely because I fail to understand a fundamental part of the syllabus, which is energy. What exactly is energy? Can we see energy? Does energy have a mass? What does energy look like? Any help would be greatly appreciated. --T.M.M. Dowd (talk) 21:36, 23 January 2010 (UTC)

Energy is that physical quantity which can do work - meaning it can exert a force through some distance. It can take many forms - most of them are not directly visible. When some object with mass has velocity, the object also has kinetic energy. When an object with mass is placed high above the ground, it has gravitational potential energy. So, you don't actually see the energy, though you can observe details about the situation from which you can deduce that there is energy present. At the level of basic physics you are working at, do not worry about energy-mass equivalence. For your purposes, energy has no mass - it is a different and unrelated physical quantity. (When you progress to a more advanced and more generalized treatment of physics, especially considering very large amounts of energy, it can be shown that in fact energy and mass are related - but in classical, every-day physics, they are separate quantities). Have you read our article on energy? Nimur (talk) 22:05, 23 January 2010 (UTC)

Energy is just energy. The everyday meaning of the word is close to its meaning in physics. --99.237.234.104 (talk) 23:06, 23 January 2010 (UTC)

Understanding the concept of "energy" alone is relatively meaningless for the most part...If you could give us an example of how exactly you don't understand it, we'd be far better set to give you more useful information. If you provided us with an example question, we wouldn't answer it, but we might be able to explain the concepts you'd need to know to do it yourself. For me, light was my biggest problem in A-level Physics...well, that and practical work...) Vimescarrot (talk) 00:22, 24 January 2010 (UTC)

See Energy. rʨanaɢ ^talk/_contribs 01:24, 24 January 2010 (UTC)

Sadly, you don't get a scientific answer - because there isn't one. So you get a touchy-feely philosophical one:

Little kids like to play the insanely annoying "why?" game. "Why can't I have chocolate? Because you've had enough already. Why is that enough? Because it's not good for you to eat only chocolate. Why isn't it? Because your body needs all sorts of different foods to work properly. Why does it need that?" ...and so on. There is no answer you can give that will make them not say "Why?" in response.

Well, I guess "energy" is the ultimate answer...it's end of the chain of reasoning and logic. Energy is that least, most minimal end of the line explanation for pretty much anything. You can't see it, feel it, taste it, smell it or hear it (although you can see, feel, taste, smell and hear the consequences of it). We can indirectly measure it - but not directly. We can predict how it changes from one form to another, we can even weigh it (thanks to E=mc²)...but we do not, cannot, directly deal with it.

For A-level physics, it's a letter in an equation. It's a convenient variable in the equation that explains how a pendulum swings - gravitational potential energy turns into kinetic energy which turns back into gravitational potential energy at the other end of the swing. You don't have to understand what the energy is - only how it changes form and is the intermediary between height and speed. Energy cannot be created or destroyed - it changes from one invisible, intangiable form to another. Set off a stick of dynamite and chemical energy changes to kinetic and acoustic energy and both eventually turn into heat. Turn the ignition key on your car and chemical energy in the battery becomes electrical energy in the wires, spins the starter, creating kinetic energy - the engine turns, the pressure in the cylinders produces heat with more electrical energy in the spark, you release chemical energy in the fuel and then more heat, causing expansion of the gasses, more kinetic energy, more heat - sound energy.

Everything that happens in the world is driven by energy changing from one form to another - but the energy itself is completely intangiable. It's a number in an equation...but it's the number that makes the universe tick over.

It's important at this stage to keep the curiosity about that intangiable at bay. Follow where the energy goes - do the math to follow it's passage through these various forms. Learn, do good work, pass exams, go to college, do more math, follow that energy, pass more exams. Get a job as theoretical physicist, get tenure, think about energy. Come back and tell me what the heck it is!

SteveBaker (talk) 01:30, 24 January 2010 (UTC)

That's the same conclusion that Richard Feynman came to here, and he got pretty frustrated with tautological non-descriptions of energy in schoolbooks ("energy makes it go"). -- Finlay McWalter • Talk 01:35, 24 January 2010 (UTC)

Yep. Feynman is my personal hero. His frustration was mostly with school physics textbooks though. The result of which that he produced a series of lectures that resulted in perhaps the finest set of physics textbooks in the world. After all of that - he really had no better insight into what energy actually is than use mere mortals. SteveBaker (talk) 01:52, 24 January 2010 (UTC)

Right. At this point, the important thing to do is to understand that this abstract concept has been shown, by experiment, to follow some quantitative rules that relate to kinematics and dynamics (i.e., position and velocity). The simple manifestations are easily defined with straightforward equations that relate energy to an object's velocity, its height above a surface, and so on. Nimur (talk) 01:50, 24 January 2010 (UTC)

True. Our OP also asks some very specific questions:

1. What exactly is energy? - As we've said. We don't have a deeper answer. Energy is the end of the line for explanation.
2. Can we see energy? - Not directly. We can use energy to light a light bulb and produce photons that carry the energy to cells in the back of our eyes which turn the photons into chemical, then electrical energy which flows into our brain and by a series of other electrical and chemical energy transitions causes us to "see" the energy...but can we actually see the energy? That's a philosophical question. Energy changed form...that's what it does.
3. Does energy have a mass? - Yes...yes-ish. E=mc²...or if you prefer, the far less memorable but equally true: m = E/c² to find the 'mass' of the energy, divide the amount of energy by the square of the speed of light. But gosh - isn't light kinda fast? Well, yeah - and fast-squared is a freaking huge number. So you take if you weigh your AA battery when it's new and again when it's run down - the difference in mass due to the loss of the energy is so unbelievably tiny that we have no way to measure it. On the other hand - if you set off a nuclear bomb, the tiny amount of mass that gets turned into energy gets multiplied by the speed of light squared and you get are really big kaboom!
4. What does energy look like? - Since we can't see it...(see answer 2), this is a non-question. What does something that you can't see look like? If a tree falls in the forest and there is no-one there to hear - does it make a sound? Dunno - ask one of those weird philosopher guys?

SteveBaker (talk) 02:13, 24 January 2010 (UTC)

@falling tree question: YES THEN NO. (You missed the crash because you weren't there. Just believe me about this.) Cuddlyable3 (talk) 16:33, 24 January 2010 (UTC)

I see that you're having problems with something that's very fundamental. Instead of giving you an answer that's technically correct but may or may not be helpful to you, I'll try to explain the concept using an analogy. Think of energy as currency in the world of physics. It is what enables you to do "work". Energy can exist in many interconvertible forms, just like (monetary) currencies. In the real world, if you want something "done", you need to spend money. In a similar way, if you want "work" done, say moving something a certain distance while opposing a force, you need to expend energy. If you pay someone money, you don't have the money anymore, but the recipient has it. In a similar way, when you expend energy, you don't have it anymore, it goes somewhere else, but is not destroyed. (Actually it's not strictly true, because of mass-energy equivalence, but until you're comfortable with the basics, it's better just to think of energy as something that's conserved, i.e. something that cannot be created or destroyed.) Can we see energy? Well, that depends on what exactly qualifies as "seeing" something. The fact is, some forms of energy (photons of visible light wavelengths) can stimulate our eyes and whereby be perceived. Does energy have mass? No. (Not exactly, but for your purpose right now, it's better to think of energy as something that's distinct and unrelated to mass.) --173.49.9.141 (talk) 03:30, 24 January 2010 (UTC)

@173.49.9.141 : As far as we know the conservation of energy is strictly true. Mass energy equivalece doesn't make it any less true. Dauto (talk) 06:27, 24 January 2010 (UTC)

Well, if you want the real McCoy about energy rather than the simplified lie-to-children version that is taught in pre-University physics, then here it is. Energy is conserved in classical physics because the laws of classical physics are are independent of translations in time (see Noether's theorem). More precisely, symmetries are associated with conserved or invariant quantities, and the conserved quantity associated with time translation symmetry is what we call "energy". Situations in which energy is dissipated into an irrecoverable form (which we call "heat") are always associated with an increase in entropy and hence a breaking of the time translation symmetry at a macroscopic level - the resulting asymmetry in time is called the arrow of time. Note that this is all within the context of classical physics (which includes special and general relativity). In quantum physics things are somewhat more complicated because conservation and symmetry laws are replaced by uncertainty relations between conjugate variables. For a more detailed explanation read Chapters 3 and 4 of Feynman's The Character of Physical Law. Gandalf61 (talk) 11:06, 24 January 2010 (UTC)