studiot

Yup, +1

Well thought out comments, Eise. +1

I think we probably are. But you seem to think it unimportant to reduce unneccessary packaging, such a step would again be win win win Since it would surely save money as well as achieving environmental aims. I regard reduction of waste as a primary step. A point or question about packaging. Surely if the primary packaging is adequate, secondary, tertiary or even (God forbid) quaternary packaging should remain uncontaminated by food, n'est pas? Again I take issue about landfill, and you seem to have ignored a perfectly good example I posted as to how and why. Further you seem to have missed entirely another point I made, which was if we made things last longer there would be less refuse material in the first place. Methane can be collected and processed by the way. This is entirely separate from the bureaucratic kneejerk that prompted the cows in nappies jokes around the planet.

Ken , I don't want you to get the impression I am getting at you personally or that I am against recycling, because neither are true. But I do think that there is much more to the subject than you suggest. In particular we need to change our outlook and behaviour, both as individuals and as a society to solve these problems. Why for instance is food packaging a problem? Well I would start by saying why is it necessary in the first place? I was a child of the post war austerity, but didn't consider myself deprived compared to the war generation before me. So I can't see why bananas need to be packaged in a plastic bag. I can't see why potatoes need a plastic bag. And I don't mean a carrier bag for either. I can't see why tins of sweetcorn need a plastic shrinkwrap. There is just too much unneccessary packaging about so we should start be getting rid of that. Then what is wrong with paper for much of the rest of it? Paper is recyclable, even if dirty, and some is biodegradable. I don't want to turn your thread into a litany of spectacular debacles by the powers that be so here is a simple anecdote about my council, which by and large is pretty efficient and decades ago started a seriously beneficial landfill program, but was stopped by the idiots in Strasbourg / Brussels morerecently. In the 1950s, the 1970s and the 1990s the centre of the town where I live was seriously flooded by the local river. Back in the 1930s the council ahd started a program of increasing the bank height with landfill materisl, but properly done. The landfill site moved slowly but steadily downriver and After a period of a decade or so the old site had settled and could be built upon. This generated a sustainable flood protected patch of building land the council could release every 10 years or so. The sale helped keep the local taxes down and generated jobs. This was win win win all round. Then came the edicts from Strasbourg and the taxes on landfill. Sidenote The politicians answer to everything is TAX IT. Recycling became politically correct overnight and a freedom of information act request to the council revealed that immediately prior to this tax the refuse collection cost about £35 per year from my local taxes. Immediatedly after it cost about £135. And yes, they introduced waste food recycling. Waste food! Remember I said I was a child of austerity? I don't waste food. Yes I have biodegradable waste material as a result of preparation etc, call it food waste if you like. But the bureaucratic mind specifies waste food. In fact we now have an assorment of containers to put different types of waste in and if the dutmen don't like collecting something they leave it in the box or more likely strew it about the roadside. We are not supposed to put 'waste food' in anything by the special biodgrabale bags (in the box) we can buy from the council, but the dustmen have yet to collect one of those bags, despite the fact it has the council's name and food waste bag clearly ptinted on it. The dustmen would rather empty the bag out and leave it behind. Yes we really do need to get our act together.

So do you want us to verify your working? it seems OK. Or do you want some explanation as to where it comes from? But it is not a derivation since you start with the Principle stated as an inequality. It is not usual to derive the HUP whn Quantum Mechanics is first introduce, the Maths is quite advanced. Teachers normally just state it as Law of Physics.

You mean there is an organisation in the world that doesn't listen to its customers? Who would have thought it? And in the IT industry as well. Of all places.

A picture of your lecture notes? So what do you want to discuss about it?

A problem with this, as I see it, is with the word 'suck'. In conventional Physics there is no such thing as suction. All instances without exception are the result of an excess of external pressure over internal.

Hello Eren, I don't want to get the wrong idea about what you are saying but I am puzzled as to why you have asked the question what is the pressue of and then answered yourself by saying that it is a mass? or a length? or a mass divided by a length? The dimensions of pressure are ML-1T-2, which means that you are missing the time component Can you explain further?

Still no working or acknowledgement of the hints I gave you yesterday?

The most recent measurements and hypotheses place the Earths core as being at least as hot as the surface of the Sun. This is consistent with modern hypotheses that require more than radioactive augmentation to account for the cooling rate and present temperature of the Earth. Yet whilst the Sun is plasma, the core is not since it is not gaseous as the pressure is too high.

Again and again I keep bumping against the loss of the obviously useful way of referencing previous posts. That of post numbering in a thread. Why can we not have it restored? I see the post counter in lists now does not include the OP so is a 'reply counter'. Some more losses has come to light. When displaying lists of posts the Originator is credited (quite rightly), but the last poster is no longer displayed. Also now the time/date of the OP is stated but not when the most recent post was made. All of this is really useful information that facilitates navigation and is still standard in many other scientific forums.

Thank you for replying. This is a Science site and a good place for precision in language is in Science. I don't just believe landfill can be good, I have positive constructive evidence for this. I even gave you some, but you largely downplayed this. Energy costs are not confined to £.s.d. There are environmental costs as well. Just suppose we built things to last longer and didn't need to repair them so often? (perfectly possible) So we wouldn't need to haul millions of tons of waste china clay material from Cornwall to the Midlands to satisfy some political imperative. This, of course, can't be done by alternative energy power but requires burning substantial amounts of fossil fuels. I hope you are not falling into the trap of claiming that all schemes are bad because some schemes are bad. I certainly don't claim that all schemes are good because some schemes are good. Yes, of course, there are good and bad schemes about for recycling, some very good, some appallingly bad. They should all be evaluated properly on their merits. Municipal Engineers have been slowly improving things for the last century or so, only to have many of their best works subverted by loudmouth, know-it-all environmentalists. In this climate, even die hard conservative politicians have latched on to the publicity value of espousing support for 'environmentalism', whilst at the same time cutting funding and permissions to environmentally benefical schemes and simultaneously promoting environmentally detrimental ones.

Glad to see you persisted to your own conclusion, without spoonfeeding. +1 Motivavation is all.

I still don't see a reply to my question in post#2 So I repeated that question in post #13, with additional amplification So why is 13 unlucky for me since I still don't see a reply to my question? Please note that answering legitimate questions is a requirement of this forum.

How did you arrive at that conclusion? When you integrate with respect to y, how do you handle any instances of 'x' ?

Hint Have you drawn a tree diagram. Can you find a spanning tree? Hint Change the description of what happens at each step. They move closer (in how many ways) They move further apart (in how many ways) Assign probabilities to each.

It is usually the limits that trip people up with multiple integrals. Have you identified which variable you must integrate first with respect to and why? Hint what cannot appear in the limit of the integral you are undertaking? What is then the effect on the limits of the second integral? For the benefit of all please confirm this is the integral you are attempting. [math]J = \int\limits_0^4 {\int\limits_{\sqrt x }^2 {\left( {1 + {y^2}\cos \left[ {x\sqrt y } \right]} \right)} } dydx[/math]

http://www.scienceforums.net/topic/75772-read-this-before-posting-in-homework-help/

Yup +1. Just like to add to this that the Curie temperature is specific to a pure substance. So mixtures such as the Earth's core will not display one definite CT. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5216106/ This also shows just how far above CT the core temperature is.

"I think it would depend on where the impact was located on the shape." That's what I said. The pointy end dropped onto a wooden floor might indent and receive some cushioning from the softer material. I would expect that to come out when the different Elasticity moduli and poisson's ratios are taken into account.

I am assuming solid glass objects. I am not sure about this prognosis. Glass marbles are spherical and pretty tough cookies. I can't remember ever seeing one shatter when dropped from twice that height onto a concrete floor. Chip maybe, but not shatter. Anyway this is all about contact forces/contact stresses, not stress distribution. Contact stresses are generally much higher than ordinary stresses in a body, but they are concentrated over the contact area. Since this is an impact loading the impact force will also be much higher than the resting force due to the weight of the glass object. Let P be the resting weight force a be the contact area CE be a constant due to the poisson's ratio and elasticities of the glass and the floor D is the diameter of the glass ball at the contact point. Then Roark gives the following formulae for [math]{{\sigma _t}}[/math], the maximum tensile stress due to contact. [math]\max \left( {{\sigma _t}} \right) = 0.2\frac{P}{{\pi {a^2}}}[/math] Where [math]{C_E} = \frac{{1 - {\nu _1}^2}}{{{E_1}}} + \frac{{1 - {\nu _2}^2}}{{{E_2}}}[/math] and [math]a = 0.721\sqrt[3]{{PD{C_E}}}[/math] You can see from these equations that the max stress is inversely proportional to the cube root of the radius of curvature of the glass ball. A spherical ball will have a constant radius of curvature, but an oval one, of the same weight, will have a pointy end of greater curvature and a flatter side of lesser curvature. Further, most of the weight volume and surface area, will be concentrated in the equatorial, flatter regions of the oval ball. So presumabably the oval ball is more likely to land on a point of lower curvature than the equivalent spherical one, thereby suffering a lower impact stress. The use of triaxial is common in earth scineces as is the splitting of the stress tensor into two tensors. Engineers in particular know that whilst it is convenient for theoreticians to collect everything together into a nice compact package, as soon as to want to work the numbers in a real world situation you have to break them all apart. In the words of a wise old engineer "You cannot avoid the arithmetic" Not long after I joined here there was a long discussion about just this, with a Russian who was doing a Phd in ice Rheology. [math]T = {T_m} + {T_D}[/math] [math]{T_m} = \left[ {\begin{array}{*{20}{c}}{{\sigma _m}} & 0 & 0 \\0 & {{\sigma _m}} & 0 \\0 & 0 & {{\sigma _m}} \\\end{array}} \right][/math] [math]{T_D} = \left[ {\begin{array}{*{20}{c}} {\frac{{\left( {2{\sigma _{xx}} - {\sigma _{yy}} - {\sigma _{zz}}} \right)}}{3}} & {{\sigma _{xy}}} & {{\sigma _{xz}}} \\ {{\sigma _{xy}}} & {\frac{{\left( {2{\sigma _{yy}} - {\sigma _{xx}} - {\sigma _{zz}}} \right)}}{3}} & {{\sigma _{yz}}} \\ {{\sigma _{xz}}} & {{\sigma _{yz}}} &{\frac{{\left( {2{\sigma _{zz}} - {\sigma _{yy}} - {\sigma _{xx}}} \right)}}{3}} \\\end{array}} \right][/math] Tm is known as the mean stress or hydrostatic stress tensor and is a summary of the pure direct stresses. TD is known as the devaitor stress tensor and is a summary of the pure shear stresses. Another term is the for triaxial the confined compression test, which can be seen in the diagram below, which also adds to my discussion with Area54.

It is more than that, and I alreadyshowed where. Why does my last post not merit and answer?

WEll thank you for the words of support, Doubbelosix. I is nice to have a new member who goes around throwing out words of common sense rather than fanciful assertions that cannot be substantiated. You want to talk about space or spacetime? Perhaps we should develop that interesting issue in another thread? I looked at your thread about this but it was all cosmological, which is not my bag really. So if you like we can start a new thread about it. I have said here that Fields belong in some particular region of space, but I haven't specified what sort of space, whether it is volumetric space or phase space for instance. The interesting thing about Fields is that if the field property in n-space is a scalar, we can drop perpendiculars to the base to create surfaces or hypersurfaces with height equal to the scalar value of that propery. The whole of shooting match exists solely in the volumetric space of n+1 dimensions, although it is difficult to imagine the 4D version needed for our 3D world. But if the Field is a vector or tensor we cannot do this. The vectors and tensors exist in a space of their own which touches our volumetric space at a single point. This is often overlooked when drawing vector arrows, but is easy to demonstrate.

Hello Area54 this is a big question. I'm not sure what your understanding is but this is often the case. But, as ever, life is actually more complicated. I admit to being a bit glib with my Fig3, but it seems to have got the main point across for light bulbs. Details of rock and soil mechanics really shoulf be in another thread but here is an outline. We haven't really discussed the spatial distribtion of the stress systems, but the work so far has been about what are called uniaxial stresses. That is stress applied in one dimension. Uniaxial compression is always accompanied by induced tension in the other two spatial axes - these are often called bursting forces or stresses. This occurs in all materials, not just rocks. This is amply demonstrated in the well known cylinder splitting test or the 'Brazilian test'. Here a cylinder of rock or soil is subject to a uniaxial compression applied across a diameter, untill it splits across the diameter. Cylinders are good because that is what core drills cut out. The test is a measure of the tensile strength of the material, although a compressive load is applied. This is an exmaple of what you are talking about. If a triaxial stress compressive is applied (simultaneous compression on all three axes) then the rock cannot fail structurally in that it will continue to carry the load as it has nowhere to go. It does however undergo plastic flow and possibly heating in these circumstance. Compressive failure may occur in bending where the material in the compression zone is crushed to a powder before any cracks in the tensile zone develop. This is the dangerous situation that reinforced concrete design codes seek to avoid by forbidding what is known as 'over reinforcement'. Failure in this mode can be sudden and without warning, catastrophic, even explosive. Of course cracks can't develop in compression zones as the compression closes them. These are a few modes of failure, if you would like to discuss these and others in rocks we will start a new thread. If you would like to expand on my explanation for glass light bulbs we can do so here.