studiot

This is a good question, but it would be helpful to know some background to establish what level to pitch an answer at. What do you know of The kinetic theory of matter The Molecular theory of matter Cooling curves for liquids. These are plots of temperature v time It is useful (and easier) to understand how solids melt before tackling how liquids freeze. Neither process is instantaneous. Dendrites can cause flash freezing at the speed of sound in the material. that is the maximum These can be very pretty http://www.msm.cam.ac.uk/phase-trans/dendrites.html https://www.google.co.uk/search?q=dendrites+freezing&tbm=isch&hl=en-GB&biw=&bih=&gbv=2&oq=dendrites+freezing&gs_l=img.3...21656.25188.0.25578.9.3.0.6.0.0.110.282.1j2.3.0....0...1ac.1.34.img..7.2.220.l7cM9r1kHL4

I'm sorry but none of this makes any sense in relation to the questions I asked in post 18. Are you saying, for instance, that there are standing waves in the air outside the bell? Perhaps I didn't make this absolutely clear, I am asking you about the sound waves in the air inside the bell, compared to the sound waves in the air outside the bell.

Another issue. My phone requires one charging voltage. My personal training logger requires another. My personal camera/projector yet another. ... ... etc So should each of these use the same connector and risk cross connection? Or should we force every device to use the same charging voltage? Devices of the world unite against the oppressive state!!! Edit some more press on this subject : Note the dates of these when you visit the links. Micro usb charger unsafe? http://www.bbc.co.uk/news/uk-england-kent-22832162 specifications http://www.bbc.co.uk/news/technology-12093013 Current report http://www.bbc.co.uk/news/technology-24726077

I agree, but with several different authorities involved are they each telling the other all they know? Is any one body collecting and collating all the available information?

CaptainPanic Yes that is really my point we need more than one type of charger available, but it is engineering common sense to restrict to the minimum few necessary. And thank you for alerting me to the whole matter since I did not know there was any action afoot. Swansont I agree that the delicacy of micro usb connections is worrying. I have seen several cameras rendered useless because of this.

I had been discussing the wave theory of light. if you want to quantize it and consider a single photon point emitter, then the uncertainty principle requires that you cannot know in which direction the photon will be emitted.

First let me apologise, since I introduced off topic material and this has clouded the pith of the discussion. However I do resent being patronised, particularly when they include "trust me (or them) I am a (or they are) experts" type comments. I have sat on national and one international Engineering Standards Committees and I can only offer that famous old phrase Enough said, back to the topic. You have not yet addressed this issue. I have a very small, simple handset that consumes very little power and offers very limited facilities (viz I can make and receive mobile calls), As a result it requires very little current to charge it and thus a small capacity charger. Other folks like to have more computing power than Cape Canaveral in their phone. Consequently their charging requirements are significantly larger than mine and this requiress much more substantial ( and expensive and resource wasteful) charging equipment. I do not begrudge them this. However I would be strongly against being forced to pay for and support charging equipment capable of doing things I do not want or need in order to charge my phone. In my opinion that is seriously bad engineering. So would you A) Ban my type of phone B) Ban their type of phone C) Force me to pay extra so that there can be a charger that can charge both phones D) Allow appropriate chargers for each phone Edit additional comment Finally, it has been my custom and practice when purchasing battery powered mobile equipment to purchase a spare battery (pack) and an off-unit charger so that I can be using and charging at the same time. As far as I know that has never been available with mobile phones, many manufacturers even going so far as to preclude the fitting of common standard rechargable cells that can be charged in common standard chargers by manufacturing unusual sized cells. I once turned some brass buttons to make up the size difference in a phone when the original batteries went dead. Addressing this issue should have been done a long time ago.

First question, does the PBS react with the hydrogen peroxide? If it doesn't then The first part (preparation of solutution A) is irrelevant. In the second part you started with a certain quantity of peroxide in 1ml of liquid and ended up with the same quantity in 100ml so you have divided the concentration by a factor of 100. In the third part you have halved the concentration by the same reasoning.

These references do you mike? https://www.google.co.uk/images?hl=en-GB&biw=&bih=&q=wignall+siberian+traps&gbv=2&sa=X&oi=image_result_group&ei=rEgiU7L-FsaZ0QX41YGICg&ved=0CEMQsAQ

All you need is time; the interesting thing, to me is not so much the fact that the disturbance will eventually reach any distance, given enough time, but that it can influence the entire volume of space spanned by all that distance and just gets thinner and thinner. Is there any limit to this?

I believe I mentioned current, not voltage? Whilst I concur that standardisation is, in principle, a good idea, slavish adherence to ill conceived policies by those who are politicians not telecoms or other electrical engineers do not fit into this category. Saying that all mobile phones must use the same charger is a bit akin to an edict that everyone in the community shall wear the same size shoes in the interests of standardisation. I am already suffering from, irresponsible harmonised wiring colours, standardised compost heap positions, flooding caused by irresponsible landfill taxes and many other indignities. A simple comment on the first on my list. If the EU beaurocracy was serious about helping its citizens in the electrical area surely a standardization of mains electrical plugs and sockets would have been better than the colour of the wiring hidden in the walls, so that any EU citizen could buy an electrical device in any country and plug it in in any other country?

I don't see why the question of what is or is not in 'empty' space is relevant. EM radiation passes perfectly satisfactorily through some pretty solid matter. Surely this is a side issue?

Note the date on the original article and the timescale. After all the current crop of politicians will have moved on and the beaurocrats retired on fat pensions. This idea belongs in the bin along with the straight banana and the prosecution of Newcastle market trader for satisfying a customer request for a pound of apples. It was clearly devised by someone who knows nothing about electricity. My small very simple mobile phone trickle charges at 0.015 amps. Look here about the needs of the gas guzzlers of the mobile phone world. https://discussions.apple.com/docs/DOC-3511 Some require more than 100 times as much current.

Who's this 'Reg'?

With the greatest respect, I think you miss my point entirely. When I was at primary school, substantially less than half passed the 11+ exam of the day. We covered mathematics that a fair proportion would never achieve if they stayed in school until their retirement age. The secondary system offered at least four different syllabuses and exams so that there was something for every one at every level. By the way this is not plea for an elitist system, just an observation that one syllabus that is suitable for both those going on to be professors of mathematics and tractor drivers is not possible in my opinion. Neither are well served by something in between.

What is the difference between the waves inside the bell and outside? Do they, for instance. have the same equation of motion or a different one? Each side of the same thin shell making essentially the same motion must be capable of imparting the same energy to the air inside and outside, yet the sound is measurably louder outside, than inside. So where did the energy go?

ajb has posted a blog entry about UK maths standards. http://blogs.scienceforums.net/ajb/?p=4260 This question and comment appears there Since there never seems to be much discussion on the original I am starting this thread about this important matter. I am inclined to say so what, what do they expect? It is my opinion that what we are seeing, not only in maths but in other subjects, is the inevitable consequence of a 'One size fits all' approach to teaching and education. People have a range of aptitude and ability for any subject or activity. So it is ridiculous in the extreme to think that a single exam will be suitable for all. In order to have any relevence and also to be fair to those of lowest ability the syllabus has to be of such a low level that they can achieve something. In theory every pupil should have been taught the skill to achieve 100% marks in their exam or it is fundamentally unfair to them. In other words, everyone is taught to the lowest common denominator.

Thank you for spotting this correction. It does not alter the fact of acoustic impedence mismatch however. The actual mode of ringing is as described in your post #11 and was stated to be the simplest available. Of course there are more complicated ones, and I look forward to your mathematical analysis of them. Please also explain (as I have done) why the sound inside the bell is necessarily different from the sound outside.

Sound is a periodic variation in pressure. To see how this happens inside a bell, we should look at ahorizontal section, rather than a vertical one as function has drawn. So to start the sequence at (1) we have a circular horizontal section, looking up into the bell. This is excited by tapping smartly with a clapper. The simplest response of the shell is to compress in one direction and elongate in another as in (2). What does not happen, if the bell rings, is for opposite sides to simultaneously move in the same direction as in (3). Opposite sides move in opposite directions. So if we add some axes to (2) we find that thare is a zone of compression (shown shaded and +) and a zone of rarefraction (shown clear and -) in (4). Further these are divided by axes, shown dashed, at 45 degrees to the normal ones. Followed by this is a springback by the shell in the opposite directions as in (5). So now the roles of compression and rarefraction are reversed. The compression zone becomes the rarefraction zone and vice versa. The dashed axes can now be seen to be lines along which there is no change and correspond to principal axes, found in other areas of mechanics. If we now consider the space either side of these dashed axes we can see that we can see that a half-wave is set up, centred on the dashed axes. I have drawn one of these in (6) As the shell springs back, it passes through the circular shape again and the half cycle in (6) returns to zero and inverts as the ellipse changes direction. It can be seen that the length of this is half a wavelength. However you should not think of this as showing sound intensity or loudness varying over the interior. Now to ties this in with what I said before. The size of my bowl makes the half wavelength about 0.2metres. Thus the resonant frequency of the air in the bowl is about 340/0.4 = 850Hz. But this is being excited by a system ringing at about 1/20th this resonant frequency, namely the stainless steel shell. So there is significant acoustic impedence mismatch between the systems. The air outside the bell is free-field and has no resonant frequency so coupling is much more efficient. If we could drive the air inside the bell at its resonant frequency it we would immediately measure an increase in loudness. This would not be the case if the quietness inside were due to interference.

If we do mean Then should we not be writing f'(x) = {f(x)}2 That is why I asked my earlier question.

I'm not sure what you are trying to say, here , enthalpy. I am having to guess at the frequency of sound produced, but a typical tinkling sound (eg middle C) has a wavelength of 3/4 of a metre. So how do you fit this into a bathroom cup or food processor bowl, to produce audio interference patterns? Edit I should make this plain that I am talking about the wavelength in air and by fitting into the cup I mean into the air inside the cup. The wavelength of a 440 Hz vibration in steel is getting on for 20 times as great, since the velocity of sound in air is around 340 m/sc and in steel around 6000 m/s.

I'm assuming you know that f'(x) is the derived function or derivative and that that means? A quadratic has the form ax2+bx+c. What function, when differentiated, leads to this quadratic? Note that you can obtain superscript (for the square) and subscript by using the X2 and X2 icons, just to the side of bold, underline etc. Yes what you must do is officially called integration, but it you can do this without a fancy name. If the derivative of bx2 is 2bx, then the function that, when differentiated, leads to 2bx is bx2. Now am not quite sure what you mean by f'(x) = f(x)2, perhaps we should clear that up, but I am assuming we can identify the constants a, b and c from this. Do you mean [math]\frac{{dy}}{{dx}} = {y^2}[/math] or [math]\frac{{dy}}{{dx}} = a{x^2}[/math]

So what did you make of my alternative suggestions? What have you deduced about f(x), given f'(x) is a quadratic? We don't do your homework for you, just try to offer helpful pointers in the right direction.

+1 ...... I like it, particularly as I also replied to the OP earlier claim, but didn't receive a sensible answer. Posts 28, 29 & 30. I also offered what was meant to be a helpful suggesion in post 27. That also went unanswered.

A hint for an alternative method. You have shown an open interval [math]\left( { - \infty ,1} \right)[/math] What happens when x=1 and when x>1 ie what could be the reason is f(x) not differentiable there? You have the y intercept. Does f(x) ever cross the x axis?