1

New Theories / Re: Global worming theory

« on: 24/03/2023 18:25:38 »

There may be a small spelling mistake in the title of this thread.   

Hence my comment about parasitic helminths. It's more fun than climate change, though worms do have a lot of impact on that too.

2

Technology / Re: Can you explain this demonstration of a capacitor?

« on: 24/03/2023 05:55:11 »

Ideally,  in the absence of any external circuit, the experimenter's hand, or residual charge on the dielectric, Q would remain constant as the dielectric is an insulator. Energy is now stored as stress in the dielectric.

3

Just Chat! / Re: Dissertation Help services for PhD and masters students

« on: 23/03/2023 16:51:23 »

Actually, AI won't help- at least in a scientific PhD.The whole point of a research degree is to discover or elucidate something that nobody else has seen or explained, so combing the internet for existing knowledge won't answer the question.

4

Technology / Re: Can you explain this demonstration of a capacitor?

« on: 22/03/2023 23:10:51 »

Sadly, vhf's wiring diagram is correct, which is why the demonstration is so bad!  Also confused by the use of the word "electrometer" which although etymologically correct, is more usually associated with measuring charge or voltage rather than current.

If the current meter had been wired "above" the capacitor in the diagram, the moveable plate would have been at ground potential, the insulating block on which the capacitor is mounted would have been unnecessary, and the ghostly hand could have been conveniently grounded with an antistatic strap. Problem is that the a maximum common mode voltage of the electronic ammeter might then have been exceeded, so (guessing a bit at the dimensions of the capacitor) you'd need a battery-powered microammeter floating at around 1000 V to show the effect - not a common piece of kit.

Worth noting that the tuning capacitor of oldfashioned radios (the ones with knobs and analog dials)  is a variable-area device, and in almost all cases the moving vanes are grounded so that the frequency doesn't drift when you put your hand on the knob. But you wouldn't expect MIT physicists to lower themselves to a 100-year-old technical trick!

5

Technology / Re: Can you explain this demonstration of a capacitor?

« on: 22/03/2023 15:11:21 »

 Is there any discernible pattern or explanation for the deflections shown on the ammeter during this part of the demonstration? 

Badly constructed equipment. The whole kit should be enclosed in a grounded Faraday cage with an extension rod to the adjusting knob. Precision electrostatics is not for amateurs.

It's a pity that they have assembled some very nice kit but not spent a few dollars on a simple dog cage to make it work properly!

6

Technology / Re: Can you explain this demonstration of a capacitor?

« on: 22/03/2023 15:04:29 »

How did they tell the charge Q to stay on the plate?

If the plate is very large and the electrometer has a very high impedance, relatively little charge will flow when the plate is moved. Keithley electrometers are pretty good in that respect but you can do better in principle with a potentiometric system and electrostatic null detector. It's the way we used to measure charge in  ionisation chambers used for radiation measurement, but it all gets a bit complicated for modern undergraduates who would probably find it offensive because it takes actual skill, can't be done with a mobile phone, and is therefore noninclusive of clumsy idiots.

7

Technology / Re: Can you explain this demonstration of a capacitor?

« on: 22/03/2023 07:59:13 »

The operator's hand is one plate of a very large capacitor, initially at earth potential (if he has bare feet) or at several kV (if he has walked over a carpet with rubber soled shoes). It's bound to have some effect on a nearby electrostatic system. Once he has touched the "grounded" equipment, his charge is equilibrated and he becomes part of the experiment.

I've not seen a Braun electroscope before - neat piece of kit! It looks as though it is connected to the insulated capacitor plate, so bringing the experimenter's hand close to it will definitely affect the charge on the insulated plate.

Crap demo!

8

Just Chat! / Re: In every country on the planet, majority of rapes are not reported.

« on: 21/03/2023 14:22:46 »

If they aren't reported, how do you determine "majority"? And "every country"?

Many crimes are unreported. The victim may fear reprisal, or consider that the effort of reporting outweighs any likely benefit, but in the case of rape there is particular problem of proof which demands evidence of penetration (not always provable) without consent (always disputable), and of taint: a significant number that do get investigated turn out to be malicious accusations so the authorities are at least cautious if not skeptical.

"Facing the abuser" is prejudicial and unnecessary. However awful the alleged crime, in a civilised country you aren't guilty until proved, so you are really talking about facing the accused. Now that isn't always required - evidence can be given by video or even audio link. But where is the right of the accused to face his accuser, as guaranteed by Magna Carta?

"Hours into getting a conviction" should be read as "a few days in police stations and  court, in order to destroy someone's life and put him in prison for several years." Seems like a fair balance of effort and reward.

Beware of poorly formed questions and facile answers that may undermine the foundations of justice.

9

Technology / How did they make the first screw?

« on: 17/03/2023 17:56:27 »

So I'm cutting a screw thread on a lathe. The lead screw turns and moves the tool along the workpiece, and the gear ratio between the chuck and the lead screw determines the pitch of my product screw. An everyday occurrence in thousands of workshops all over the world.

But the lead screw needs to be at least as precise as the one I'm making.

So how did they make the first lead screw?

10

Just Chat! / Re: Generally speaking, how would Brits respond if...

« on: 14/03/2023 17:29:11 »

Tens of thousands of people queued to walk past the Queen's coffin.
In a city of ten million that means well over 99% didn't bother.

Those that did queued for up to 2 days to do so, and the show was time limited: there simply wasn't any chance of the other 99% getting in. The procession from Balmoral to London and the funeral were major television events watched by almost everyone who wasn't at the roadside.

11

Chemistry / Re: Can glucose be synthesized without organic inputs as sources?

« on: 12/03/2023 23:21:26 »

Of course, there are peop[le who believe that, one day, we may be able to create living things from inanimate materials.

It would be difficult and pointless, but it has already happened without human or divine intervention so it's clearly not impossible.

12

Just Chat! / Re: On Gender Reassignment...

« on: 11/03/2023 17:52:33 »

I'm all for people doing whatever they want as long as (a) it doesn't harm or disadvantage anyone else and (b) I don't have to pay for it. But (a) isn't satisfied when a male rapist or professional athlete says he is a woman.

13

Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: 11/03/2023 17:45:41 »

So Planck was wrong after all.

14

Just Chat! / Re: How Human Morality 'Evolves'...

« on: 10/03/2023 16:35:44 »

Evolution favors the successful or efficient without defining "better" in any other sense. So an evolving morality would have justified enslaving or eliminating everyone except white anglosaxon protestants because they invented the steam engine and the machine gun. Hence Nazism.

A more generally acceptable morality involves accommodation and diversity, which is counter-evolutionary.

15

Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: 10/03/2023 16:21:10 »

Part of your practical problem would be the amplitude range as well as the frequency range of your black body radiation. Evan's lasers at least restrict the frequency range to near-negligible so it's not inconceivable that you could look for missing lines in their uniformly high intensity spectrum but if we look inside an ideal carbon spherical shell* at red heat, the tiniest surface imperfection will alter the Planck resonance spectrum by adding or subtracting wavelengths equal to arbitrary multiples of the height of the imperfection, and all against the background of every other surface element doing its bit!


*mathematicians and theoretical physicists may like cubes, but engineers ask awkward questions about what happens in the corners, so physicists prefer to use spherical shells.

16

Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: 10/03/2023 11:52:53 »

A waveguide is effectively a long, thin oven designed to support one particular mode and frequency. It can obviously support harmonics but these are usually filtered out or not generated in the first instance.

Much the same applies to wind instruments. A flute extracts a fairly pure sine wave from the exciting edge tone, whereas a conical-bore instrument like a saxophone carries a lot more overtones.

17

Plant Sciences, Zoology & Evolution / Re: Are the majority of domesticated cats and dogs content with coexisting?

« on: 10/03/2023 11:49:05 »

They are as variable as humans in their tolerance of one another.

Most will adapt to living in the same house but with slightly different attitudes: dogs seem to regard it (and the human residents) as a domain to be secured and protected against all intruders, whilst cats treat it as a residential club with room service and only object to feline non-members entering the premises. Dogs quickly learn to pee and poo outside, whilst cats tend to demand (or nominate) ensuite facilities.

Order is quickly established in my experience. "I could swallow you in one mouthful" "Not if I scratch your eyes out first".  "I eat from the big bowl, with a few vegetables" "I only eat meat, from the small bowl".

18

New Theories / Re: Universal Utopia? What's The Universal Terminal Goal?

« on: 04/03/2023 10:00:09 »

Most economies depend on the production of waste. If everything worked perfectly and lasted for ever, manufacturing industry would cease. You can't sell makeup remover to people with tattooed faces.

19

New Theories / Re: Universal Utopia? What's The Universal Terminal Goal?

« on: 03/03/2023 13:52:24 »

More of productive people is good for the economic system, which means that they will help achieving its terminal goal.

Assuming, of course, that the  terminal goal is to overpopulate the planet with humans who turn their environment into toxic waste.

20

New Theories / Re: Universal Utopia? What's The Universal Terminal Goal?

« on: 02/03/2023 23:37:40 »

Yes. But it also includes estimates for unreported cash flows from illegal drugs, prostitution, etc.,  so taken along with mortgage and other debt interest payments,"economic growth" may not be the Good Thing that economists and politicians want you to believe.