1

Physics, Astronomy & Cosmology / shape change with no energy transfer?

« on: 11/05/2022 23:02:58 »

As an aside from the discussion on energy transfer between ice and water, consider a cube of ice immersed in water, all at 0 deg C.

All the molecules are jiggling about at random. Those at the edges and corners of the cube have the fewest bonds to other members of the cube so are most likely to acquire sufficient kinetic energy to leave the solid and enter the liquid.

It takes 334 joule/gram (latent heat of fusion)  x 3 x 10^-23 gram (mass of a water molecule) to release one molecule from ice. So by leaving, our exceptionally energetic molecule reduces the temperature (the average kinetic energy of all the remaining molecules) of the ice by a tiny amount.

So a water molecule could now attach itself to the ice to restore thermal equilibrium. But the most probable place for the impact to occur is on a flat surface, not an edge.

Thus if we maintain absolute equality of temperature between the ice and the water, the cube will gradually turn into a sphere!

2

General Science / Why do waves move towards the beach?

« on: 10/05/2022 20:02:03 »

Waves are caused by the interaction of wind and tide.

Wind direction varies, tides flow in and out.

But the waves always travel towards the beach.

Why?

3

New Theories / Does this answer evolution-deniers?

« on: 20/02/2022 10:49:54 »

I will take seriously any argument that debunks evolution, if and only if it is proposed by someone who looks exactly like both of his/her parents. Anyone else is an embodiment of evolution.

4

New Theories / Do rocket engines violate the equivalence principle?

« on: 24/11/2021 15:37:41 »

[This topic was split from here: https://www.thenakedscientists.com/forum/index.php?topic=59801.0]

This raises a different question of equivalence.

Assume a rocket with a very large but finite amount of fuel, accelerating at 1g. The occupant feels as though he is standing on a planet, but knows he is accelerating because his fuel gauge is decreasing.

5

That CAN'T be true! / Why can't water vapour be the driver of today's climate change?

« on: 27/10/2021 12:00:36 »

PS does anyone have an authoritative atmospheric infrared absorption spectrum (i.e. one based on verifiable recent measurements) that doesn't show the CO2 bands as saturated? All those I can find suggest that it cannot be the cause of further global warming. I'm all in favour of abandoning fossil fuels (sound political and economic sense) but future generations might question the reason why we did so, and I'd hate to be associated with bad science!

6

Just Chat! / Equal or equivalent?

« on: 21/10/2021 00:31:59 »

Mathematically, and indeed in all scientific phraseology, equivalent (≡) is "stronger" than equal (=). If A ≡ B then all their properties match for all tests we can apply. The same terminology is used in engineering: an equivalent component will have exactly the same specification as the original but a different part number because, say, it comes from a different manufacturer or was made for a different customer. X = Y, on the other hand, may only be true for a limited range of variables, maybe only a single point where two curves intersect.

In sociology, the terms are used in precisely the opposite sense. "Equivalent but separate is not equal" is the  essence of all desegregation slogans, and we have an intuitive grasp of its meaning: equivalent implies difference, not similarity.

How come?

7

Technology / Would minirockets have any military value?

« on: 09/10/2021 11:38:08 »

Tangmere air museum is well worth a visit: a pleasant day out in the country, good cafe, well organised car park, and incidentally several amazing historic aircraft. Obviously I went for the food, fresh air, and to study the development of WAAF uniforms and hairstyles,  but I just happened  by sheer chance to wander into the English Electric Lightning simulator where I was persuaded against my mature judgement by an ex-RAF instructor to fly a 30 minute ground attack mission. Which activated the brain, several days later.

The gun pod, which only carries 7 seconds' worth of ammunition (at >1000 rounds per minute, that's still a lot of damage!), is extremely heavy, because the barrels have to contain the energy of a 30 mm cannon shell. The cartridge casing and the propellant are left behind when any gun is fired.

Now the object of the exercise is to deliver a lot of kinetic energy to the target, so I wonder if this might be done more efficiently by replacing the explosive propellant with a solid rocket charge, thus turning the barrel into an open tube with very little strength requirement, delivering more of the payload to the target, and having the characteristic of accelerating in flight rather than slowing down as a bullet does. No reason why the barrel shouldn't be rifled, or the missile grooved, so as far as the physics is concerned you end up with a lighter weapon with the same accuracy as a gun, that delivers more bang for your buck.

Military rockets are a few large devices delivering an expensive payload with a low rate of fire, from a suborbital missile down to an RPG,  but I wonder what technical issues prevent the development of a "machine rocket launcher"  to deliver a high rate of fire of small (say 30 mm?) rockets in the same space as a conventional  airborne cannon?     

8

Just Chat! / Why is pi irrational?

« on: 01/09/2021 14:25:18 »

One for the mathematicians! Please provide an explanation suitable for whatever age we introduce π into school mathematics.

9

Just Chat! / Is this the answer to cheap electricity?

« on: 25/07/2021 23:31:51 »

I mentioned in these forums that EON, among others, seem to be misleading potential customers by advertising "100% renewable electricity at no extra cost". So I wrote to them asking how they could justify their claim, since right now  only 10% of grid input is from renewables and EON supply around 20% of total demand.

I just received an excellent reply. They buy some of their electricity from 100% renewable generators, and don't charge the customer according to the source of whatever they supply. So the advert is literally true but obviously misleading.

So I have replied thus:

"Some of the stuff in my pockets is 100% Bank of England currency. In future I will pay my bill with whatever comes to hand at the time - banknotes, old surgical masks, shopping lists, parking fine notices, etc. Thus, exactly as you calculate the renewable electricity supplied to me, in full and final settlement of your bill, you will receive 100% legal tender and a fair bit of scrap paper to cover the remaining 90% of the invoice. If you do not agree to this arrangement, I will refer the matter to the Advertising Standards Authority."

10

Just Chat! / What do you mean by "random"?

« on: 03/07/2021 18:22:24 »

Common problem: I need to traceably randomise 100 patients for a clinical trial. So as they are recruited, I assign each one a random number from 00 to 99, then, say, give the trial drug to those with odd numbers and the placebo to the evens.How do I generate those random numbers?

A. Take two 10-sided dice, one numbered 0 to 9 and the other, 00 to 90. Roll the dice and there's a random two-digit integer for each patient, with a 1 in 100 chance of it being any value from 00 to 99.

B. put 100 counters in a hat, give it a good shake, draw one at a time and discard it: same probability of it being any value from 00 to 99.

What is the probability that I will assign a given number to two patients?  In case A, almost 1. In case B, zero.

In case A I cannot guess what the next number will be, so that's really random. In case B, my guess will become more accurate as the numbers are assigned, and I know exactly what the 100th number will be, so it's not quite as random.

It all depends on what you mean by "random".

11

Plant Sciences, Zoology & Evolution / How do chickens work?

« on: 16/06/2021 10:06:34 »

Birds lay between one and a dozen eggs, once or twice a year, and incubate them until they hatch.

Except domestic chickens, which lay one egg every day and mostly walk away from it. Clearly not a great survival strategy for a ground-nesting forest dweller. How and when did they get from there to here?

12

Technology / Fusion still in retreat?

« on: 26/05/2021 09:33:10 »

Under the headline "Pollution-free electricity moves a step closer to reality thanks to British scientific breakthrough", Sky News today revealed that the UKAEA has developed a new exhaust pipe for a tokamak:

"It's a pivotal development for the UK's plan to put a fusion power plant on the grid by the early 2040s - and for bringing low-carbon energy from fusion to the world."

Fusion power was "only 5 years away" when ZETA was unveiled in 1957, and has steadily retreated at a rate of around 2.8 months per year ever since.

Would anyone care to calculate when we will see the first actual fusion kWh on the grid, and how long it will take to repay the R&D costs of getting there? 

Edison's light bulb patent was granted in 1879 and by 1882 ConEd was supplying mains power to Manhattan.

What has gone wrong?

13

Technology / EoN a con?

« on: 30/04/2021 09:44:32 »

EoN supplies about 15% of the UK's electricity. Their current advertisement says they supply 100% renewables. But right now, and for the past month, only about 12% of the total UK  supply has been from renewables, and many smaller companies make the same claim.
How do they do it?   

14

The Environment / How come the ice core temperature curve always leads the CO2 curve?

« on: 24/01/2021 23:21:41 »

Here's the Vostok ice core  data that makes me skeptical
The timescale reads from left to right and three features are strikingly clear

The temperature rises are very steep compared with the asymptotic falls, indicating a positive feedback mechanism in play
The temperature curve always leads the CO2 curve, implying that CO2 is an effect, not a cause.
The most recent feature shows a continuous steep rise in temperature beginning 25,000 years ago, with a few hiccups in the last 5000 years or so. On a geological scale, it is no different from previous steep rises.

These curves were published in the 2001 "Summary Report for Policymakers" of the IPCC but the anomalies were not highlighted or explained. I attended one of the early presentations of that report and quickly lost confidence in it as John Houghton (editor) introduced himself as a "committed Christian". I'm very wary of people who parade prejudice and superstition as a virtue: science isn't like that.

Moderator's note: This thread about interpreting historical ice cores was split off from "How could you stop the earth's poles from warming?", which is more forward-looking and action-oriented.
- Please post comments in the appropriate thread.

15

Plant Sciences, Zoology & Evolution / Why is compost black?

« on: 04/01/2021 00:01:51 »

I spent a happy couple of hours today spreading some good home-made organic muck  on the vegetable beds.

Said compost began its career as grass clippings, sawdust, vegetable peelings, paper, fruit skins, fallen leaves, dead flowers, chicken poo, and weeds. None of which was black. But after a couple of years it was uniformly black. Why?   

16

COVID-19 / The first sign of common sense?

« on: 15/12/2020 10:54:13 »

The Independent

Netherlands imposes strict five-week lockdown lasting through Christmas.

The Netherlands will go into a tough five-week Covid-19 lockdown following a spike in infections, with the closure of schools, non-essential shops, and museums and gyms, Dutch prime minister Mark Rutte announced on Monday.

17

COVID-19 / What happened here?

« on: 01/12/2020 12:09:43 »

Is this evidence of resurrection, or tampering with UK death statistics?

18

COVID-19 / Is the R value a useful parameter?

« on: 03/08/2020 15:46:07 »

Apologies for a long post, but it's something I've had in mind for some years and seems very appropriate right now.

It is doubly unfortunate that epidemiologists have chosen the symbol R to denote the “effective reproduction number” of an infective agent, and politicians have seized upon R as an indication of viral virulence, or their “success” in controlling a pandemic.

For anyone unacquainted with the terminology, R is the average number of persons infected by a single carrier of a disease. That sentence will have triggered a “caution” response in numerate readers, and a howl of derision from anyone who has travelled in a crowded train. If the specific infectivity of a virus is constant, R is obviously dependent on the behavior of the carriers, not the virus: R_COVID = 0 for a hermit in a desert, maybe 20 for someone who sneezes his way around the London Circle Line at 8 am. 

As shown by experiment, there is no scientific justification for relaxing social distancing or quarantine rules when R decreases: doing so merely allows it to increase again.  And R is an average of the entire population exposed by all recent behaviors including total isolation: it does not indicate the likelihood of any individual becoming infected at a particular time and place.  R is an effect, not a cause or a decision parameter.

Why doubly unfortunate? Because some years ago I proposed a risk index R as a means of communicating risk to the public, and the present COVID pandemic demands a simple, efficient parameter that can be used for public information and emergency planning. So in deference to the World Health Organisation, I’d like to relaunch the risk index with the Cyrillic symbol Я (pronounced Ya).

Define Я = 10 + log₁₀ P where P is the probability of an event.

If the event is inevitable, P = 1 and Я = 10

If the event is so unlikely that no living human will see it,  Я < 0.1

The logarithmic scale is actually familiar to the public and consistent with our intuitive appreciation of risk. Winds of Beaufort force below 4 are of no consequence. Force 5 is inconvenient, 6 is mildly hazardous and 10 is “seldom experienced inland” with trees uprooted and major structural damage. Likewise the Richter earthquake scale: up to 4 is of scientific interest, 5 – 6 causes recoverable damage and anything above 8 is a disaster.

In everyday life we consider Я ≤ 5 “worth it” for the fun or benefit. The UK annual risk index for death in a road accident is about 5, but deep sea fishing with an annual Я_DEATH approaching 7 is a dangerous profession in northern waters.

My original interest was in efficiently communicating the risk of diagnostic x-rays. The natural incidence of cancer gives Я_{<DEATH|CANCER>}  ≈ 9.4 (no apologies to this audience for Dirac notation, and I’m sure Joe Public will get the idea pretty quickly).  Against this, we have Я ≤ 4 for a dental x-ray (negligible – could save you pain and infection, and safer than driving to the clinic) and 7 for a repeated abdominal CT (worth the risk to avert a greater one).

In a pandemic, I think honest public information demands activity-specific values of Я_<Y|X> , the risk index of an individual contracting Y whilst doing X. Early in the UK outbreak I cancelled a biannual jazz concert on the estimated Я_<COVID|GIG> of 8.4 (unacceptable, however good the band) given the likely size and packing density of the audience and the probable local incidence of infection.  I take no pleasure in being right in this instance – by the original date, two members of the prospective audience of 100 were indeed infectious, one becoming very seriously ill a few days later.

It should be possible to estimate and publish general Я values for, say, working in an office, a ventilated factory, or an outdoor team, and travelling to work by bus or train.  You can subtract an appropriate value for each type of face mask. Those of a social science bent might study crowd behavior in theatres, pubs etc and on beaches, and estimate appropriate Я values that would be far more meaningful and specific than the current global R that allegedly “informs” political decisions. Individuals can then make properly informed choices about their work and leisure. 

19

New Theories / Can heat affect Earth's rotation?

« on: 01/08/2020 11:28:25 »

[Mod edit: Topic split from "Can windmills affect Earth's rotation?"]
https://www.thenakedscientists.com/forum/index.php?topic=80136.0


Any windmill extracts kinetic energy which we eventually turn into heat.

Ignoring second-order effects such as thermal winds, the source of kinetic energy is the rotational energy of the planet, so it must eventually stop spinning.

Now that really will induce some climate change!   

20

COVID-19 / Can we organise an effective national quarantine?

« on: 05/07/2020 23:55:16 »

Assuming that COVID remains a significant disruptor of daily life for the next 6 months, would this suggestion find any favour?

Starting now, government prepares for a full national quarantine period beginning on Christmas Eve. Don't call it "lockdown" because that sounds like a punishment: it's a cure.

Starting today, we build national stocks of basic food and hygiene supplies. No different from provisioning a ship for a month at sea, except we have enough to deliver 4 x 1 week packages to everyone. Actually it's easier than provisioning a ship as we can assume that everyone has access to clean water, so no limit on dehydrated foodstuffs.

On 18 December we begin distributing the first week's packages with a "do not open before 24 December" label. Remote locations will get a whole month's supply but most of the mainland will get 4 deliveries on the same day each week. Not a big deal as the Post Office and courier services will be shifting a lot of packages anyway.

From midnight on 24 Dec there is a compulsory prohibition on all but essential travel for 2 weeks. Essential means only those services and personnel previously identified as such, patients needing urgent treatment, and corpses. All retail and high street trading is closed. Included in essential services is a door-to-door COVID testing program for everyone. No need for tracing as nobody is going anywhere. There being nobody in the streets apart from emergency services, we should have enough police manpower to help with testing. On 7 January those households with a clean bill of health are released and all others remain under curfew until 28 January. 

Given 6 months notice and the experience of the current shambles, people should be able to cope with staying at home during what is mostly a holiday period anyway, and everyone gets the "clarity" that seems to be the current watchword. There being negligible business or holiday travel, hotels can accommodate the homeless and anyone arriving from overseas, and gear up for providing compulsory 2 week quarantine for all arriving passengers until further notice.