sethoflagos

Fracture mechanics can become very involved very quickly, but if we limit our scope to simple brittle fracture... Both fracture propagation speed and elastic recoil shock of a fractured solid are functions of the speed of sound in that material and typically many times the speed of sound in air. Therefore a space opens up faster than that information can be passed to the surrounding air resulting in a substantial vacuum. Eventually the pressure wave information gets passed on and the air rushes in at its own sonic speed to fill the void. When the void is filled the air it is brought to a halt with extreme rapidity and releases it's kinetic energy primarily as acoustic shock waves (variously known as 'surge' or 'water hammer'). This is the process that produces the loud 'crack' of a bullwhip. Now rather than one big whip imagine several thousand cellulose fibre 'whips' doing the same thing per second at a microscopic scale. That's the sound (at least a major component of it) of paper tearing.

Like a customised self-gravitating body ~100+ km diameter built from carefully redirected small asteroids to put it into a path of ejection from the solar system? Internal thermal energy may be a viable long term energy source (or nuclear). Deep subterranean accommodation caverns should give reasonable protection from small collisions. Not sure I'd pick the lifestyle choice myself...

RIP Dickey Betts

I can buy this. Nitrogen fixation is energetically expensive, so the evolution of BNF would not be favoured unless abiotic processes failed to satisfy the biological demand for fixed nitrogen. However, the claimed unavailability of molybdenum simply does not square with an early appearance of Mo based BNF. The two are mutually contradictory. The reference quoted for this low Mo condition is "Proterozoic ocean chemistry and evolution: a bioinorganic bridge?", Anbor & Knoll, Science 297 (2002). I've not seen the full paper, but the abstract describes the limited availability of (by inference) molybdenum under the Proterozoic (543 - 2,500 mya) conditions of oxic surface waters and anoxic depths. This is one and a half billion years after the period we are discussing and a very different chemical redox environment. Our present interest is in the availability of Mo3+ and Mo4+ in the anoxic surface waters of the early Archaean around 4 billion years ago, not Mo6+ in oxic waters of a couple of billion years later. Having now invested a bit of time in this, I'm not seeing any relevant evidence for the claim of low Mo availabilty during the period of interest.

Me neither. Unaltered sediments from those far distant times are exceedingly rare. Examples from just the right place and right moment are likely long gone. And yet life definitely started therefore there was sufficient fixed nitrogen around. So both the 'no molybdenum' and 'no fixed nitrogen' claims are belied by the undisputable evidence of our existence. It seems that somebody somewhere is extrapolating a small and questionable data set way beyond its scope of applicability.

Far be it from me to question this, yet the paper itself offers strong evidence of the early appearance of Mo based BNF which implies that Mo was definitely available to life in the oceans. Something of a paradox. Molybdenum is not a rare element, especially around hydrothermal sites. Perhaps its low apparent oceanic concentration at that time was a reflection of an intense biological demand that kept it locked up in biomass. Just a thought.

Bear in mind that for its first 2 billion years, the earth was a temperate water world with much reduced continents, and a mildly reducing atmosphere of N2 and CO2 perhaps with minor CO and CH4. Sediments from that period (unlike later deposits) generally feature pyrite, pitchblende and siderite indicative of reducing conditions throughout the ocean basins. Levels of volcanic activity were considerably higher than today, including forms like kimberlite pipes that recycled material from very deep within the earth's mantle, including large amounts of the heavier transition metals. However, it is possible that modern plate tectonics didn't really get going until after the major chemosynthesis and retinal based photosynthesis processes had developed so this happened in a somewhat different geological setting than we see today. Thermal vents must surely have played a part in the development of life - too good an opportunity to miss, but with many of the key micronutrients widely distributed in maybe more soluble reduced forms throughout the oceans, there seems less need for all the ingredients for abiogenesis to be concentrated at a single source location. Splitting up the task between a diverse range of mineralised environments, that may or may not have been closely spaced massively improves the odds in favour.

Who are the primary producers in the thriving communities around deep ocean hydrothermal vents? Not much photosynthesis going on down there.

The air bubbles reduce the overall density of the fluid mixture in the tube. Ignoring complications like friction etc., hydrostatic equilibrium demands that fluid surface height (measured from the base of the tube) multiplied by density is the same both inside and outside the tube. In principle, half the density, double the height. Though there are always losses in practice.

You might find this article on Prandtl number interesting and relevant. https://www.sciencedirect.com/topics/engineering/prandtl-number Edit: actually don't. Some of the numbers are out by several orders of magnitude (!) But the Wikipedia page on Prandtl number is okay for the first few paragraphs.

Add to this that gas thermal conductivity is directly proportional to CV favouring selection of the low specific heat monatomic gases, and that argon is relatively cheaply available from air liquidation facilities.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2907586/ states that 'possibly endosymbiotic' rod-like methanogenic prokaryotes were seen in close proximity to the hydrogenosomes during scanning electron microscopy. If so then perhaps the circle is closed at least in part by the reasonably exothermic (and biological carbon fixing) of CO2 reduction by H2.

Understand this and you clear the confusion. F = ma Weight = Mass x gravitational acceleration lb force = lb mass x g/32.2 ie if we equate weight numerically with mass, we're implicitly adopting some unit of acceleration that has the numerical value of 1 at the earth's surface. As @exchemist has pointed out, this creates a great deal of needless complications in US technical literature. Many equations end up littered with this dimensional constant of 32.2 simply to maintain this unity factor between weight and mass. Either that or adopt that most wonderfully named of all units, the slug foot. See https://en.wikipedia.org/wiki/Gc_(engineering) Only approximately. The higher levels of the earth's atmosphere are subject to a lower gravitational acceleration due to their increased distance from the centre of mass so they weigh less per unit mass. This illustrates quite nicely how careless application of the unity assumption can simply lead to incorrect results.

If you can't be arsed to improve the clarity and coherence of your own argument then why should anybody else do it for you? It isn't as if it's a position worth defending.

Your pressure unit is in reality lb force / in2 so the result is not lb but lb force. ie. the force exerted in opposition to the gravitational acceleration of a mass of 1 lb at the Earth's surface. It's a sloppily presented question: lb / in2 is not a correct unit of pressure. g is implicit in both sides of the equation, but cancels.

And perhaps you should too. I can sympathise with the conceit of not capitalizing 'god', but why on earth are you giving him a double initial 'g' in bei Gott? And while you're at it, please clarify the context of both 'he' and 'it'. Your anaphora is clear as mud. It's almost as if you're trying to deliberately obscure your meaning.

Others made it relevant whether he wished it or not. Your criticism seems nonsensical.

Your 'connotes' is contradicted in the OP: ... like believing that the Conservative Party are going to win a majority at the next British general election. Or Trump 'won' the last US presidential election. Given the vociferous and frequently malicious nature of the attacks on evolutionary biology by the US christian right in particular, I think Dawkins strikes the right tone. Sufficiently punchy to attract the attention of the uncommitted, yet not sinking to the level of the opposition. Got to remember who the target audience is - it isn't to the regular contributors to scienceforums.net. We more than any should allow him his leeway and applaud his contribution. Personally, I'd have gone for the title 'Satanic Verses' but I understand someone else got there first.

A domestic dwelling can have an adverse power factor so the phi in pf = cos(phi) is real and measureable especially if it's heavy on the ac and refrigerator loads (as we are, we've got a mechanic tinkering with our knackered gen set as I type!). The 4,000+ km wavelength I mentioned applies to the time of flight effect over long transmission lines. By the time you see an ac voltage (or current) peak, the last one is long gone. So the phase change over a 10 metre distance is oto 4 second of arc. Good luck measuring that with a multimetre 😊

V here really stands for voltage difference, not absolute voltage. So when you say: Your question reads as if the voltage gradient along the wire is zero. Did you intend that the two ends of the wire are maintained at a constant voltage difference? This would make more sense.

I think the correct answer to this rather odd question is yes, though if the wire has any resistance then that uniform current is zero. In the absence of reactive elements (capacitors or inductors) a constant current implies a constant voltage gradient. If the load is purely resistive, then the current is in phase with the voltage. A purely capacitive load will make current lead voltage by 90o. A purely inductive load will cause a 90o lag. Practical loads fall somewhere in between these extremes. The variation 'along the wire length' needs to take into account that the electrical field propagates at some substantial fraction of the speed of light, so the wavelength is oto 4,000 km at 50 Hz.

This reminds me of how pressure is not an 'energy' but mediates the transfer of internal energy of a gas which is a function of temperature alone. However, pressure is a 'force' so that analogy breaks down. I did wonder why electron charge cropped up as a coefficient on both terms of the Lorentz force, both the E and vxB terms. So without q there is no electromagnetic force. Is this what you mean? That the B field is merely a mechanism for transforming dynamic changes to the Coulomb force into a torsional effect?

I suspect that the guarded responses you've received to this query so far are because the simple answer we used to be given at school was bowlocks and sort of implied the existence of magnetic monopoles. Hence no self-respecting physicist will go down that path. As I don't fall into the above category, I'm quite content to picture the energy source as a form of potential energy created by the separation between the nail and the magnet. Much akin to gravitational or (ahem) Coulomb potential. As nail approaches magnet, potential energy begets kinetic energy begets heat (in collision) producing a new magnet that is the sum of its initial magnetic dipole moments, just as a meteor descending to earth creates a new body that is the sum of their individual masses. Now I am expecting this simplistic picture to be shot down in flames, but then I too will be wondering (in the absence of electrical current) where the energy came from.

If all spatial dimensions loop back on themselves seamlessly, so that whichever direction you travel in, after n light years you are back where you started, then what does 'centre' even mean? It's definitely finite with a volume oto (n light years)3. But there is no point more remote from the boundary than any other because there is no boundary. All points within the space are geometrically exactly equivalent.

Pretty sure there's a x-post here with @exchemist so briefly: If we're starting from your declared position of maximum attraction, we're moving against an attraction force for 900; then with a weakened repulsive force (poles wide apart); then against the same repulsive force; then finally with the mirror image of the attraction of the initial power stroke. In the absence of a proper mathematical analysis, by symmetry we have a nett zero sum. And then there's cam friction and the hysteresis braking mentioned earlier. Granted I've ignored secondary effects of the movement of the magnets themselves but frankly, that's beyond my pay scale. Suffice to say, if there was anything to see here, Faraday would have found it back in the day I think. Looks right enough, so you've got the 1800 phase shift covered. Shall we leave the +/-900 phase shifts to the OP?