studiot

The simple expectation for the Hall coefficient and conductivity/resistivity is based on the 'free electron theory' or Drude theory. This theory is corpuscular and assumes that the charge carriers act like gaseous atoms in the kinetic theory. Effects such as Hall and conductivity are dependent upon the number/density of carriers, regarded as individual corpuscles and independent of the effects of the lattice and wave mechanics. This theory is only really successful for alkali metals and unsuitable for other materials. Better theories from wave/quantum mechanics show that the De Broglie wave suffers interference in the lattice such that, although its main component is in the direction of the corpuscular vector, the wave also has components in other directions. The main component is perpendicular to the imposed magnetic field, but the others are not and so are affected by it differently, leading to a skewing / diminishing / reversal of the Hall voltage. This is the best easy explanation I can offer.

I asked because you second sentence is not another way of putting your first one. Your first one included all animals. However your question is a fair one and related to the OP. A possible answer is the OP idea that the prevailing conditions constrain or force animal size is a good one. Unfortunately he is focusing on the wrong conditions IMHO. So the main condition determining size is thought to be the availability of food. It is interesting to note that under suitable conditions species can shrink as well as grow. For example the fossil pygmy elephants found in some Mediterranean islands, thought to have crossed from Africa when the med was dry and then shrunk to fit the food supply when stranded on islands. https://en.wikipedia.org/wiki/Dwarf_elephant Note the biggest dinosaurs were thought to be vegetarian, like the blue whale in the picture. Plants in the time of the dinosaurs were larger than today, so perhaps obtaining and digesting enough to grow to the larger size was easier then. Predators obviously had to become large enough to overcome the behemoths, would a modern lion be capable of taking one on?

Which one do you want? http://imgur.com/gallery/HyfVJIu @ diouro Did you find anything useful in the BBC programs I indicated? There was also a similar recent BBC series about the history of the Earth, incorporating our best knowledge to date. https://www.google.co.uk/search?q=BBC+Earth+Story&hl=en-GB&gbv=2&tbm=isch&oq=BBC+Earth+Story&gs_l=img.3..0i24l4.1672.5422.0.5859.15.12.0.3.3.0.187.1654.0j11.11.0....0...1ac.1.34.img..1.14.1699.FSAy_-R-Yq4 There is an explanation of why we think there has been no significant change to the Earth's mass or size since the accretion phase. This is simply because large bodies grow at the expense of smaller ones so a large body will sweep its orbital zone relative clear of material. The only way the body can then grow is by attracting another large body that is passing, but this has not happened in the last few thousand million years. As to dinosaurs themselves, both yourself and Michel might like to try to read a copy of Professor Bakker's book Dinosaur Heresies. https://www.google.co.uk/search?q=Bakker+Dinosaur+Heresies&hl=en-GB&gbv=2&tbm=isch&oq=Bakker+Dinosaur+Heresies&gs_l=img.3...85922.92016.0.92250.24.11.0.13.13.0.172.1284.1j9.10.0....0...1ac.1.34.img..10.14.1300.iPyLKOi5V6Y As regards the atmosphere, the only comprehensive history over geological timescales that I know of is here https://www.google.co.uk/search?q=the+emerald+planet&hl=en-GB&gbv=2&tbm=isch&oq=the+emerald+planet&gs_l=img.3..0j0i24l2.2281.6250.0.6484.18.11.0.7.7.0.234.1561.0j9j1.10.0....0...1ac.1.34.img..1.17.1748.vKBElm1nouE

I find it most impolite to be addressed as 'u'. Further I understand simulation theory to be something quite different from what your other respondents appear to be talking about. So please explain what you mean by simulation theory and thus provide a proper opening post I can respond to.

With respect, Sensei, how doe you idea answer the question about showing the difference between dia, para and ferro magnetism? I mentioned susceptibility because the sign of this property determines whether the material will be attracted onto a given magnetic field or repelled out of it.

I don't understand. How can F(y) be a function? The integral (if it exists, which I haven't checked) is a definite integral and therefore a pure number and therefore a constant, not a function at all. and what is y anyway?

I think it was this series, you want the 'making of' bit. https://www.google.co.uk/search?hl=en-GB&source=hp&biw=&bih=&q=bbc+walking+with+the+dinosaurs&gbv=2&oq=BBC+the+dinosaurs&gs_l=heirloom-hp.1.0.0i7i30l10.1110.9625.0.14422.17.13.0.4.4.0.203.1719.1j10j1.12.0....0...1ac.1.34.heirloom-hp..1.16.1875.k85sPJZYSlI BTW the book I mentioned has quite about about flight and the difference between bees, hummingbirds and human aircraft. Also water craft and water insects.

There have been too many acrimonious threads, but let me observe that this is not one of them so far. I am not that interested in biological history but I do remember a recent BBC series about dinosaurs where they also published some very interesting material. This was about the 'engineering' of the dinosaurs. Essentially they used CGI techniques to create 'film' of the time, and the studies they did to try to work out the mechanics of dinosaur bodies and locomotion was highly interesting. Several preciously unknown matters were discovered during this. Since there is no geological evidence that our Earth has had substantially different radii or gravity since it coalesced the work was done using modern day values. I cannot remember the title, perhaps another can help here? As an engineer you may be interested in readingthis book by Steven Vogel Cats Paws and Catapaults The author compares human and nature's solutions to various engineering challenges. This is not about the dinosaurs directly, but illuminating all the same.

If I give you the following information you should be able to research a suitable demonstration Paramagnetic materials have a permeability slightly greater than unity and small positive susceptibility. Examples are aluminium and platinum. Ferromagnetic materials have a permeability much greater than unity and large positive susceptibility. Examples are iron, nickel and cobalt. Diamagnetic materials have a permeability less than unity and negative susceptibility. Examples are copper, gold and bismuth.

Hmm, let me see if I understand you. Thank you for the further details. This may or may not have meaning. So are you are measuring 1) Radon buildup in a 'radon proof' sampling vessel? That is on days 1-3 100 units collect in the jar, on days 4-6 a further hundred units collect and on days 7-9 a further hundred units collect. or 2) An increasing rate of radon escape So that on days 1-3, the sampling jar collects 100 units, on days 4-6 a fresh sampling jar collects 200 units and on days 7-9 another fresh jar collects 300 units Either way does an average have any real meaning? If you have a bunch of numbers, you can always calculate an 'average', but this number does not always have any real meaning. For instance, say I go into a hardware shop and buy 4 nails, 50mm, 75mm, 100mm, 150mm Is the average nail length of any use? But again say I buy 4 six inch nails of measured length 150mm, 149mm, 151mm, 150mm. What does this average tell us? An average is one measure of a single number used to represent a bunch of figures. There are other measures that may be more appropriate. Some might be the median, (half the values fall above and half below) or the mode (the peak value in a frequency curve) But again it may be appropriate to report intervals rather than single values. This is often the case, especially when readings or measurements are sparse and / you have no idea of the true population. Then we come to the subject of errors and 'error propagation', which I don't think you are using appropriately from what you have so far described. Are you actually asking If my measurements are 100+- 3 ; 200+-5; 300+-8 Is the average 200 and if so how do I combine the tolerances to obtain an average tolerance? (This is not error propagation by the way)

You seem to have a good grasp of mathematical notation, but It is not clear to me what you are measuring. Is the 100; 200; 300 a sequence of cumulative measurements of one location, or individual estimates of small parts of one location or what? Statistical methods for treating cumulative frequency distributions are different from point value distributions. You also say somerhing about measuring different things (underlined in your passage) Can you explain this further? I think once your methodology is sorted out, the appropriate techniques can be determined and applied.

Real live monkeys and a dolly bird. http://www.bbc.co.uk/news/36767373

How about some pictures of these patterns?

With that list, this book should definitely be on your shelf. http://eu.wiley.com/WileyCDA/WileyTitle/productCd-3527406999.html

+1, good question swans. If your target is hard ( and brittle) then the speartip will be supplying energy to newly created fracture surface in order to penetrate. No large fracture force is required just a continuous supply of energy, so maximum impact kinetic energy is required. If your target is soft, as I suspect, then the target material reflows around the speartip and no fracture surface is created. In this case driving the spear in is more like piledriving or nail driving and the maximum driving force is required. This, of course, means maximum impact momentum.

Let's keep this in perspective. Resnick and Halliday, despite its title struggles as a first year university textbook in Physics. It would barely have got me through the A levels I took fifty years ago. It is aimed at students of technical disciplines such as Engineering, Chemistry and the like who need a basic background in Physics to supplement their main subject. So practice in Physics questions really depends upon what you want to do with your R&H background. The best way to find worked problems is to narrow down the subject area and look for texts in those areas. At tertiary level subjects texts tend to cover a narrower aspect than high schooltexts. For example electrical engineering, fluid mechanics, dynamics, heat, materials science, and so on all offer many excellent example calculation books Second hand texts can be had for pence. So help us to help you by identifying your particular areas of interest.

To the best of our knowledge, yes.

There is no evidence of significant mass change for the Earth since the original accretion phase in the history of the solar system 4 billion+ years ago. This accretion phase cleared most of the available material in our vicinity so we only get the odd wanderer or loose the odd atmospheric molecule nowadays. . Edit, Note the dinosaurs died out about 60 million years ago, a mere eyeblink in relation to the Earth's age. Also this was not the biggest mass extinction event, which occurred nearly 200 million years before the dinosaurs

Hello Kelly, It would be useful to tell us more about the effects you wish to create. Water itself will act as a paint thinner. When you say water colour do you mean water colour or are you including what used to be called poster colour (powder paint you mix up with water) ? What sort of quantity are you thinking of? An addition of colourless alcohol or glycol would change the viscoscity of the water (which is already low) and have the advantage of evaporating along with the water. I assume you don't want to add sticky substances like gels to the mix. The change is complicated and depends upon the concentration, but the viscosity will be higher than either individual liquid. I remember an artist who created the most dramatic effects about 50 years ago by curdling indian ink with a small amount of water. I will try to look out a photo of the effects, but this will take me a couple of weeks. Another thing to consider is surface tension. This is likely to be more significant in thin films, such as used by artists. The surface tension is reduced by adding a colourless detergent, such as used in chemical laboratories for cleaning glassware. This does not leave a residue on the glass so is ideal for your application.

I thought swansont might say that, but in fluids there are two methods of analysis, relative to the flow and relative to a fixed reference. The velocity is constant, relative to the flowlines. But this is a boring non productive argument. capiert this might help if you can follow it. http://www.efm.leeds.ac.uk/CIVE/FluidsLevel1/Unit03/T5.html

It would be generous and helpful if we could all dispense with comments like the underlined henceforth. In brief answer to the rest of your post: When a fluid, travelling at constant fluid velocity, passes round a bend or elbow in a pipe, the pipe exerts force on the fluid to turn it around the bend. In turn the fluid exerts a reaction force on the pipeline. This force can be considerable, enough to blow the joints or burst the line (as I have seen). Or the line may simply be displaced. It is this force that causes a hosepipe to snake about. This force is there even without friction. If we add friction into the theory the fluid will exert a bursting force on every flange and coupling joint, even in a straight pipline. Does this help

I beg to differ, this statement is ambiguous at best and can be misleading. I have personal experience of disasters that occur when engineers fail to appreciate the need for proper thrust blocks in pipelines. Please can we just collectively establish what capiert is trying to present and move forward?

I agree this is a static electricity effect. +1

No your question is neither silly nor simple, but I hesitate to answer for safety reasons without considerably more information. First and foremost Why do you think the liquid (?) is acid? Is there a label? (it could always be mislabelled) Some people keep other corrosive liquids in bottles, such as bleach or caustic soda. Secondly what do you want to do with the stuff? Now for some data specific quesions What colour is the liquid? Does it have a smell (care needed here in testing)? It can't be hydroflouric acid if it is in a glass bottle. How big is the bottle? Can you post a photo? You say it is in the garage. It could be drain cleaner, rust remover, concrete cleaner (all of which could be pinkish phosphoric acid) battery acid. Over to you.

+1 for providing a model or example format when querying someone's post. The one thing I did not mean to imply is that a flux of photons constitutes a wave. Remember that this thread concerns the wave theory of light so my response was in those terms. The wave theory regards light as two connected fields, an electric one and a magnetic one. It does not address specific corspuscular properties also possessed by light, that are best described in terms of corpuscles (photons). The idea behind my phraseology is that a lightwave comprises a series of periodically varying electric fields, which generate varying magnetic fields, which generate vary electric fields as the lightwave moves along. These fields do not exist at a particular point, before the lightwave arrives there and cease to exist there after the lightwave has passed. It is in that sense that the lightwave carries its own medium, the fields are the 'medium'. Does this help?