1

General Science / Dry Docks

« on: 23/03/2023 13:10:42 »

Having seen ships in dry dock from time to time, and been struck by how precarious the supports looked, I'm having difficulty in being surprised at the "capsize" of the Petrel.

The system I recall seeing has the keel, and I presume the majority of the weight, supported on blocks on the floor, with props at the sides holding the ship upright. With the ship balanced on the keel and minimal load on the props, since they were wedged and in compression only it would take relatively little force from a gust of wind to momentarily release the compression at the windward side, at which point all the props fall out.

It looks like there's about 900mē of windage, which would give about 20 tons at 45mph, perhaps that's enough if the props were put in carelessly, especially if there are repeated nudges from repeated gusts over a long period of time.


Petrel.png (4.86 kB . 707x677 - viewed 229 times)

2

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

« on: 22/03/2023 17:33:05 »

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.

The Keithley electrometer is the ammeter with a low impedance, and the electroscope is the voltmeter with a high impedance, but yes, the 'scope draws a small current, like all voltmeters. Measuring off the screen, the electroscope must be 2000-3000 times smaller than the capacitor.

3

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

« on: 22/03/2023 14:35:48 »

I don't know where the ammeter is connected.

Yes you do, follow the wiring:


MIT vid.png (13.57 kB . 1048x591 - viewed 929 times)

So there is at least one path from plate to plate through the ammeter.

No there isn't, the power supply has been disconnected, so the only connnection to the live plate is the insulated support on the stand, and the electroscope.

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

Yes, as above, the knob is on the live side of the meter.

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

« on: 22/03/2023 14:06:44 »

the first deflection of the Ammeter during the first twist is to the right.   All the other twists and you have a deflection to the left

No, you can see that every time his finger makes contact with the knob, the meter gives a kick to the right.

The adjuster knob is on the earth side of the capacitor, but the live side of the electrometer, so any charge on the experimenter will leak to the power supply earth through the meter.

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Technology / Re: How did they make the first screw?

« on: 18/03/2023 10:44:30 »

A winch and cable will give you linear motion from rotary.

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Physiology & Medicine / Re: How important is penis size in regards to the actual sex act?

« on: 17/03/2023 21:47:09 »

"How important is penis size in regards to the actual sex act?"
Not very.
Ask any lesbian.

Have you seen the size of dildos?

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The Environment / Re: Tipping Point?

« on: 14/03/2023 17:49:21 »

Surely, we're missing the point when we talk of 'climate change'?  Why not focus on the complete anthropogenic ecocide?

The problem is the overconsumption of natural resources in general, and the capacity of the atmosphere to serve as a dustbin for our waste carbon is just one of them. If we ever get a clean source of energy people will think problem over, and the overconsumption of other resources will accelerate.

As long as the only game in politics is economic growth, and people compete for status by trying to consume more than their peers, there won't be a solution.

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General Science / Re: Do You Dream in Monochrome or Colour?

« on: 14/03/2023 17:32:05 »

Makes me miss Champix - they gave you such vivid dreams

I was on metronidazole for a week or two once, that gave me surreal dreams that were quite good fun.

In one, I was at the top of a large stone tower like a lighthouse, and it had a spiral ramp inside like a helter skelter. I raced down the ramp like I was on roller skates, but I had no skates, my feet were gliding an inch or two above the ramp like a maglev. When I got to the bottom I shot out of the door, and then raced down a big hill.

In another, I was flying like a bird.

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Plant Sciences, Zoology & Evolution / Re: How Do You Repel A Very Persistent Cat?

« on: 13/03/2023 00:21:11 »

I just got cat repellent, and it is only working slightly

What are you doing with it if you've got cats of your own?

I once had a cat leaving muddy paw prints warming itself on the bonnet of my car, so when I went out there and saw it one day, I crept back in and fetched a bucket of water. That saw it off, and no more paw prints on the bonnet.

My mum was adopted by a cat that had obviously run away from a bad home. She started giving it saucers of milk when it came and sat on her kitchen windowsill, so it decided to stay where it was welcome, and treated kindly.

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Physiology & Medicine / Re: Why do some people not get hangovers?

« on: 11/03/2023 12:43:18 »

I think the only time I've had a noticeable hangover was after a night out where there were large help-yourself jugs of red wine on the tables. Red wine isn't something I ever normally drink, and I didn't really recognise the hangover for what it probably was at the time.

I can remember getting blotto at a cocktail party once, because I don't normally drink shorts either, but despite riding home with my head out of the window of a mate's car decorating it with second hand cocktails, I don't recall any big hangover afterwards.

11

Just Chat! / Re: What is your theodicy?

« on: 08/03/2023 16:37:29 »

ChatGPT is a Product, not an Oracle.

It's quite handy for those irritating Amazon emails asking for a review though:

As I engage with this kitchen roll holder, I find myself transported into a realm of ontological uncertainty. Is it an object of utility or an artefact of aesthetic contemplation? Does its form exist solely to serve function or does it transcend its function and become an embodiment of pure form? These are the questions that plague my mind as I grapple with the complexities of this postmodernist masterpiece.

At first glance, the holder appears as a simple cylindrical structure, a geometric form that is ubiquitous in our contemporary society. However, upon closer inspection, one is struck by the intricate web of intersecting lines that define its surface. These lines seem to weave in and out of each other, creating an illusion of depth and motion. They are not merely lines, but rather entities that exist in a state of perpetual flux, constantly shifting and morphing as they interact with one another.

The holder's base is a sturdy and stable platform, providing a solid foundation upon which the cylindrical structure rests. Its smooth, polished surface seems to reflect the light in an almost ethereal manner, as if the holder itself is imbued with a divine radiance. The base is not just a functional aspect of the holder, but rather an integral part of its aesthetic identity, a canvas upon which the holder's form is allowed to shine.

But perhaps the most striking feature of this kitchen roll holder is its ability to subvert our expectations of what a kitchen roll holder should be. Instead of a traditional vertical design that requires the roll to be loaded from the top, this holder utilizes a horizontal design that allows the roll to be loaded from the side. This seemingly insignificant deviation from convention serves to create a sense of dissonance in the viewer, challenging our preconceived notions of what a kitchen roll holder should look like.

The holder's materiality is also an aspect that demands attention. Its surface is composed of a high-quality stainless steel, a material that is both durable and visually striking. The steel's reflective properties allow the holder to seamlessly blend into its surroundings, creating a sense of spatial continuity that is rarely achieved in kitchenware design.

Furthermore, the holder's form seems to suggest a certain degree of modularity. Its cylindrical shape and simple base allow it to be easily incorporated into a wide range of kitchen design schemes, while its horizontal loading mechanism allows for maximum flexibility in terms of placement. This modularity speaks to a broader trend in contemporary design, one that values versatility and adaptability over rigid adherence to tradition.

In conclusion, this kitchen roll holder represents the apex of postmodernist design. Its ability to simultaneously subvert and celebrate convention speaks to a larger philosophical project that seeks to challenge our assumptions about the world around us. Its intricate form and materiality demand our attention, inviting us to contemplate the complexities of contemporary design in all its multifaceted glory. To engage with this holder is to engage with a work of art, one that transcends its function and becomes a testament to the boundless potential of human creativity.

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Physiology & Medicine / Re: Why do some people not get hangovers?

« on: 07/03/2023 10:48:54 »

I'm quite tolerant of alcohol in that I don't usually get hangovers, but not very tolerant in that I can't drink very much.

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The Environment / Re: Global Warming. long term effects.

« on: 06/03/2023 13:02:06 »

Politicians should not panic about warming as it is a natural reaction to the increase in world population.

So is extinction.

There are 4 times as many people now that in 1945 at end of WW2 who need to be fed with carbohydrates, meat and live in new warm houses and drive cars to work.  It is their human right to have all these things.

There is no human rights clause in the laws of physics.

So the increase in CO2 is to be expected as a necessity and we must live with it.

So human rights extend to owning a home, but not to having it safe from burning down in a wildfire.

Sea weeds like kelp are ideal for sequesting  carbon dioxide into the oceans and these grow extremely quickly.

Once the seaweed has grown to maturity, where do you store it all to prevent it from releasing the carbon as it decomposes, and to make space for the next generation of seaweed that's going to absorb the next batch of carbon emissions?

So it looks as if the sea rise will be around 36 mm per decade or one and a half inches which should be easily containable.

That's not a very long term argument. There are plenty of maps published showing how much of the land mass will be under water by the time sea level rise is done.

Thus the need to educate developing economies and encourage family planning is thus obviously the way forward

Keep up, Hans Rosling explains here that the birth rate already is under control, and the present rise in population is what's already baked in to the system as todays kids grow up and have kids of their own. If the birth rate doesn't go back up again for any reason, the population will stabilise at ~ 11bn.

improve their standard of living with all the advantages of high standards of living that prosperous states provide..

The problem is that 12% of the population is hogging 85% of the wealth. With a fairly trivial cut in consumption by the rich, the poor can enjoy a huge increase in living standards without any increase in cabon emissions.

What's needed is a means of curbing economic growth, because that's what's ultimately unsustainable, and as someone above said, that's always taken as a prerequisite for entry into political circles. We need to learn to take the benefit of productivity improvements as an increase in leisure time instead of an increase in consumption, but to stand any chance of making some headway in that direction requires some understanding of the psychology of status competition among both politicians and the general population.

We're locked into this endless cycle of consuming more and more because a consumer society is one in which people's satus is determined by how much they consume: the Jones's are only content when they have a bigger car than the Smiths, and the Smiths when they have a bigger car than the Jones's etc. The obvious problem is that this is a zero-sum game, because no amount of wealth can ever satisfy both the Jones's and the Smiths at the same time, and so the cycle of waste just gets perpetuated.

Ending climate change depends on ending growth, and ending growth depends on dealing with status competition in a less destructive way, but consumption is a more powerful status symbol than leisure time.

14

General Science / Re: In controlled demolitions, what procedures are applied to prevent air toxicity?

« on: 05/03/2023 13:35:40 »

it's not realistic to ascribe subsequent deaths to that particular incident.

Nor should they deny that all subsequent deaths were unrelated to exposure at work.

It is difficult for the legal system to deal with cases where there may have been an increased risk of some adverse event from an alleged cause, but also the possibility that it may have been unrelated to the alleged cause.
- The only options seem to be that it was or was not related to the alleged cause.
- This is especially difficult in the very litigious USA
- Penalties/compensation seems to be quite random (from a distance)

In Australia, it is accepted that if you worked in an asbestos mine or an asbestos factory and later develop mesothelioma , that your condition is work-related. But life expectancy after diagnosis is around 9 months, and it takes a similar time for the compensation scheme to swing into action. 

Armley asbestos disaster is one of Britain's biggest industrial accidents with ~300 dead, and counting, but it's little known. From 1874 to 1959 the Roberts factory was spreading asbestos all over Armley, kids used to have snowball fights with the dust, and about 1000 homes were tested and found to be contaminated, but weren't made safe until 2008. The story was exposed by the Yorkshire Post in the 1970s when the mesothelioma incidence started rising, and Armley now has the highest rate in the country.

My parents lived just down the road when they were first married, if I'd been born 10 years earlier I could have been one of the kids throwing snowballs.

15

Physiology & Medicine / Re: is psychiatric labelling complete nonsense?

« on: 05/03/2023 12:48:10 »

So this Smail guy doesn't know what he is talking about.

The NHS clearly thought he did, or they wouldn't have employed him as head of Nottingham mental health services. Someone who thinks that Ad Hominem is a rational way to go about refuting an argument doesn't, though.

It's about 20 years since I read Smail, so I'm reluctant to get into arguing detail I don't recall, but I think most of his book related to therapy for problems like anxiety & depression, which are the biggest cause of mental illness that account for 8-9% of the population, and about 40% of all mental illness.

None of which is relevant to Smail's argument, which you are bending over backwards to avoid.

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Chemistry / Re: Why adding a fizzy drink to ice does the temp drop below the temp of the ice?

« on: 26/02/2023 18:24:47 »

I heard that

Have you checked to see whether it does?

I can see why the evaporation of CO2 will reduce the temperature, with or without the ice.

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Physiology & Medicine / Re: What's the future of tattoo removal?

« on: 25/02/2023 11:51:45 »

I recently had a mri and one of the many contraindications was having a tattoo.

That's interesting, I've had several mri scans, but I don't recall tattoos baing on the list. That might just be because I don't have a tattoo though. Is there metal in the pigments?

I once had a girlfriend with a large scar on her arm,
"Is that scar where you've had a tattoo removed?"
"Yes, but I don't want to talk about it, ok"
So we didn't.

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Geology, Palaeontology & Archaeology / Re: Why do insects fly?

« on: 20/02/2023 11:32:52 »

chicken (bees, butterflies, etc) or egg (flowering plants)? which evolved first, and why? 

Shouldn't that read "chicken (bees, butterflies, etc) or egg (pollen)? which evolved first, and why?"?

In which case, I'd say pollen, because it can spread on the wind. I recall watching clouds of pollen dispersing from the fir trees in my garden on a windy day.

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Physics, Astronomy & Cosmology / Re: Will tidal power cause the moon to crash into us?

« on: 08/02/2023 12:15:47 »

The rotational kinetic energy of the Earth is truly immense.....Human use of that energy would be minuscule by comparison.

Kinetic energy: 259000YJ
Global annual energy consumption: 634PJpa

259000YJ/634PJpa = 409 billion years

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Technology / Re: Has anyone exploited the balancing half-sphere for electricity production?

« on: 04/02/2023 19:01:34 »

What is the proposed source of energy causing it to wobble?

It could be people, or it could be wind outside, or a mix of wind+magnets.  What do you think?

Or to put it another way, what do you think a lump of concrete brings to the party that other systems don't already have?