exchemist

Yes but again nothing about how a driver would use the manual adjustment on old cars. Nice MGB GT, though. I had a teal blue roadster in the early 80s. XDL152L. I looked up the reg on DVLC a couple of years ago - and she’s still going! I sold her when I went off to Dubai in 1983.

Ah so it was indeed to do with variability in octane rating of the fuel. But would this have been in place of the kind of automatic adjustment of ignition timing I described on my Morris Minor, or just a supplementary control, to extend the range of adjustment to cope with fuel variation? I have now looked up the history and found the concept of "octane rating" appeared towards the end of the 1920s. It looks as if the run up to WW2 led to development of high octane aviation fuel. Shell apparently pioneered "100 octane" aviation fuel, which became adopted as standard in the high compression ratio turbocharged aviation engines of the time. However there was no real standardising of octane ratings in road-going motor fuel until the 1950s. So maybe this accounts for the need to alter the timing manually, depending on the quality of fuel available.

That is why one needs the ignition timing to vary with engine speed and load but my question was not that. It was about why it was apparently controlled manually on early vehicles and what would be the circumstances under which the driver would adjust it.

I am somewhat intrigued by the bit about the spark being advanced. I seem to recall the spark advance was controlled pneumatically on my old Morris Minor (1961 model) by a diaphragm in the distributor, connected to the low pressure in the inlet manifold. But I have a faint memory of being in an ancient vehicle, perhaps a school bus, in which there was a control on the dashboard with "advance" and "retard" on it, presumably so the driver could alter the ignition timing manually. Seems rather extraordinary. Was this common in the early motoring era and why was it done? I wonder if it was before fuel ignition quality (knock rating) was standardised.

So are removable oven doors. Maybe this topic will get all us oldies fessing up to various mechanical amateur repair experiences. I’m reminded of James Thurber’s comments on psychological traumas inflicted by early motor cars:”Yonder toddles an ancient who once tried to crank an old Reo with the spark advanced…”

In my limited experience, trying to repair anything with a spring-loaded mechanism is fraught with danger. There is often some kind of mechanical advantage issue, whereby the spring needs to be very powerful to exert force at what is in effect the wrong end of a lever. Fiddling with such things is a recipe for taking your finger off or something.

For some reason it seems to be only the Italians that have exploited this, in their aliscafi on the Italian Lakes (and Emilio Largo’s Disco Volante in Thunderball) I remember someone once made a hydrofoil bicycle, with a propeller driven by pedals, which could just about beat a sculler in a racing shell. The snag was it had to be launched artificially, as the energy barrier to getting it up on its foils was too much for the athlete pedalling.

I'm no physicist but I had understood there is an unresolved incompatibility between the two, i.e. as the two theories stand today if one is right then the other can't be, and that is why there is a search for a resolution that unifies them. But no doubt a physicist will show up and explain.

This "Engineering Made Easy" is a YouTube Indian woo channel: https://www.youtube.com/@EngineeringMadeEasy There is a whole bank of videos taking turd about "spirituality". It has nothing whatsoever to do with either engineering or science. I think this poster is just spamming. It certainly does not belong in the Physics section anyway.

What great flood has science proven? Please provide a reference.

Interesting example of a faux ami. I gather the English word calamity comes, via Old French, from Latin calamitas, which has no connection to calamus.

Yes of course they are not real. There is all kinds of stuff on the internet, a lot of it fictional or misrepresented. You must know that, surely? Anyone with any sense will check the sources of what they find by browsing the internet, to see whether it is what it may initially seem to be and if it is genuine. This is basic critical thinking in the internet era. When I saw your picture of the giant skeleton, I looked up "giant skeleton picture" on the internet and within 30 seconds I had a written explanation of this Milan sculpture, complete with telltale details about the long nose the sculptor includes as a "signature" feature and which you can see in the picture. So the moral of this story is: do at least a bit of basic research before asking questions that risk making you look a fool.

Looks like a modern take on Ozymandias.

Sure. But with a half life that long, I'd have thought you would never be able to measure a discernible decrease in radioactivity. But thinking more about it, I suppose with a big enough sample, if you can detect every individual decay event, you can count the decays of individual atoms and, knowing how many atoms there are in your sample, you can work out the decay rate that way.

It's a sculpture in Milan, you credulous person: https://www.atlasobscura.com/places/giant-skeleton-sculpture

Uranium-lead radiometric dating makes use of an isotope with a half life of billions of years: https://en.wikipedia.org/wiki/Uranium–lead_dating Mind you, I’m buggered if I know how the hell they determine a half life that long. Must be by dating rocks using other, shorter, half lives, I imagine, and then inferring from that the half life of U238.

Oh yes sweetbreads are very good. I've had them on a couple of occasions and thought they had a slightly similar taste to that of liver, though far more delicate. But it seems they can be two types of offal: either the pancreas or the thymus gland. I can understand why the former might have a taste similar to liver but, not really the thymus gland. (By the way, the reference to thymus glands reminds me of the idiotic story of a man allegedly strangled by his own thymus gland in cold weather, posted on another forum by a nutter who specialises in posting daft questions and asking, mock-innocently, if there is any truth in them. )

Military Watch Magazine appears to be an outlet for Russian propaganda: https://mediabiasfactcheck.com/military-watch-magazine-bias/ I would not trust their figures.

Agree about the Iranian economy. I read in the Financial Times that they can struggle on for about a year without oil income. Iran is an industrial nation of 90million with quite a lot of other regional exports, not just a bunch of desert tribesmen with oil wells. So they can, apparently, last a year. Whereas the US mid terms are in 6 months and a blockaded Strait ensures higher inflation and fuel prices for US voters. Therefore I imagine Iran can afford to tough it out and wait, while the electoral urgency mounts for Trump. They can see the US public turning against him. They can also see he is going nuts, hence their on-line trolling to wind him up in the hope of further mad outbursts that will damage him further. (He now seems to be doing his best to alienate both the Catholics and the Evangelical Right, quite unnecessarily.)

OK so 0.07N/m. Let's say someone spread-eagled on the water has a total waterline length of 9m. That will generate ~0.6N of upthrust, compared to a body weight , for a (light) 60kg person of ~600N, i.e. of the order of 0.1% of what is required to make them float. But away from the question about floating bodies, yes at the cm scale surface tension starts to make itself felt. I have a badly designed colander with 0.5cm holes in stainless steel and I can never get things in it to drain properly. My parsley, coriander or whatever is always dripping wet, no matter how long it is left to drain.

You mean surface tension, like a pond skater? That would depend on the length of the contact line between water and skin. But surely the effect would be negligible, wouldn’t it?

Erm, that doesn't seem to mean very much, to be honest. I really don't think it's a good idea to bandy around sciency words without thinking what they mean. If all protons are the same that means they do NOT have unique features, surely?

There is a lot of chalk in Dorset, whereas I don’t think there is much in Devon and Somerset. Lying on your back in water can’t increase buoyancy, as that has nothing to do with surface area. Buoyancy is a matter of how much liquid is displaced by the floating object, cf. Archimedes’ Principle. But if you lie on your back with your lungs partly inflated, your mouth and nose should be above the water level, whereas if you are vertical the water level is somewhere around your eyes (I think). It makes quite a difference how much your chest is inflated as obviously your chest displaces more water then so you float higher.

What do you mean by “quantum information”? (I’ve an awful feeling you have been at the woo again😄)

A wave is not energy. A wave has energy, among its various properties. Energy is just a property of a physical system, like momentum. A wave is created by a displacement of some medium from its equilibrium value, e.g. when you drop a stone into a pond and a wave spreads out. Water has been displaced, giving it extra energy and the displacement travels outward in the form of a wave. A vibrating object can give rise to a wave if it is in contact with a medium which it is able to displace. That will absorb energy from the vibration and damp it. A vibrating tuning fork displaces the air it is in contact with, creating the sound waves that you hear. And this will damp out the vibration eventually.