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General Science / Re: How many calories do you use to chop meat?

« on: Today at 21:11:49 »

As BC pointed out earlier, the quiescent consumption of a human being is around 100 calories per hour. The most extreme physical labour corresponds to a useful output of about 100 watts but few people can maintain that for more than an hour at a time, the probable world records being held by cross-channel manpowered flight pilots, who were champion cyclists able to maintain 200 W for an hour. Cutting meat uses the arm muscles, which are far weaker than the legs. 10W of useful work is pretty good for a day's duration.

10 Wh = 36000 joules = 8.6 Calories

You can do the measurements several ways. Measuring oxygen consumption isn't particularly easy as you have to analyse the exhaled gas, which still contains a lot of oxygen. Easier to measure exhaled CO2. You can simulate the task with ropes and paddles in a water bath and measure the temperature rise of the water, or use a dynamo load and measure the work electrically. Maybe put a force transducer and accelerometer in the knife handle.

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Chemistry / Re: Can the Periodic Table be arranged as a stepped pyramid?

« on: Today at 20:58:01 »

It would be amusing to play the tune without the words, and see if an audience of chemists could sing the song as the panels light up. I've sung it enough times, but even though I have a periodic table shower curtain (I test my anorak every morning), I don't think I could place the elements on a blank canvas.

The problem with the stacked matrix representation, as with many of Mendeleev's early attempts at categorisation of the elements, is that it isn't easily predictive of chemical or physical behavior. The power of the conventional layout is (was) in predicting the properties of hitherto undiscovered elements.

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General Science / Re: What is centrifugal force?

« on: Today at 13:52:44 »

Whatever definition we give to "away", that tangential movement has NOTHING TO DO with any centrifugal force, because, since the very moment you cut the string, both centripetal and centrifugal force DOESN´T EXIST any more ... Therefore, the stone keeps the velocity vector it has at that moment ! (Newton´s First Motion Law).

If it moves away when I cut the string, the string must have been exerting some force on it before the cut.

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Physics, Astronomy & Cosmology / Re: What does the term 'time' relate to in time dilation?

« on: Today at 13:49:17 »

Not sure why entropy is frame-dependent. It is a scalar quantity whose increase denotes a conventional increase in time. A specific example would be radioactive decay.

If c is constant, we can always determine the sequence of events A and B.

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General Science / Re: How many calories do you use to chop meat?

« on: Today at 13:36:57 »

Nothing abnormal about paelobiologists or butchers' assistants! My estimate was based on about 7 hours of actual cutting and dicing with professional knives. In a domestic kitchen, you might spend 10 minutes dicing enough meat for 3 or 4 people, maybe 1 - 2 Calories allowing for a relatively blunt knife and lack of skill.

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Physics, Astronomy & Cosmology / Re: What does the term 'time' relate to in time dilation?

« on: Today at 09:29:23 »

At the risk of being dragged into philosophy, the notion of "elapsed" presumes a direction. We are fairly relaxed about the scalar distance between A and B and the vector distance from A to B, because the context makes it obvious and for the most part |A→B| = |A←B|, but it isn't always so.

If we accept Eddington's "entropy is time's arrow" then we have an independent definition of the directon of sequential events (positive if the entropy of the universe has increased between A and B) and hence a concept of elapsed time. But history, archaeology, carbon dating and the whole of forensic science, is about reconstructing events in reversed time, not merely establishing a sequence but also calculating the scalar modulus of temporal separation.

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General Science / Re: What is centrifugal force?

« on: Today at 09:13:05 »

I wish there was a "tongue in cheek" emoticon, but Nemesis Pete is just as effective!

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Physiology & Medicine / Re: Are there gender differences in how body hair grows?

« on: Yesterday at 18:23:28 »

Long female hair is a cultural phenomenon that doesn't apply in many parts of Africa. The preferred length of male hair varies with time but is to some extent circumscribed by age too: many women can retain a full head of hair into senility, but most men lose it, so there is sometimes a cultural preference for a very short crop among male over-50's, whilst older women may prefer a "volumising" style of waving or combing to disguise any loss.

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Physics, Astronomy & Cosmology / Re: What does the term 'time' relate to in time dilation?

« on: Yesterday at 18:12:32 »

Some good facts about time. They are what we can say about time in nature. I don't think anyone knows what time is.

Oh come now! A cow is a bovine quadruped that moos and poos, with milk in the middle. Time is what separates sequential events. These are definitions. Only a philosopher would pretend not to know what a cow "is". Farmers and scientists have more important things to think about, because we work with animals and time.

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General Science / Re: The sounds of science...

« on: Yesterday at 18:03:04 »

Wonderful, thanks BC! Brought back memories of 1964, sitting in a lecture theatre at the Cavendish Lab!

Colin: I haven't got the NASA recordings to open yet, but will keep trying.

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General Science / Re: How many calories do you use to chop meat?

« on: Yesterday at 17:06:48 »

A butcher's assistant probably expends about 60 calories per day cutting meat.

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General Science / Re: The sounds of science...

« on: Yesterday at 17:03:19 »

I'm trying to find a recording of "whistlers" - audiofrequency electromagnetic waves resulting from lightning disturbances travelling along the earth's magnetic lines of force. Wikipedia has a nice spectrogram but I can't locate an audio clip. Can anyone help?

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Physics, Astronomy & Cosmology / Re: Can a wall of mushrooms absorb harmful gamma radiation?

« on: Yesterday at 09:51:30 »

Cheddar cheese (sorry I don't have the figures for Wensleydale)  is about 50% water, 30% fat (plenty of thermalising protons)and 15% protein. It contains less than 0.5% calcium. Obviously the perfect neutron shield.

Way off the subject, but when we were first establishing the national breast screening service, I needed a precisely reproducible substitute for breast tissue for testing new x-ray installations. It turned out that Gouda cheese has a very tight specification, is just the right density, and with two wedges, you can simulate a range of breast thicknesses. No neutrons, but I learned a lot about the photon scattering and absorption properties of cheese.

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General Science / Re: What is centrifugal force?

« on: Yesterday at 09:32:02 »

In the previous discussion Alancalverd stated that there was no such thing as centrifugal force.

I sincerely hope I didn't! Others, and the writers of trendy textbooks, deny its existence, but I have felt the tug on the string, and wondered why, if the only force on a rotating object is centripetal, the tyres fly off wheels at high speed and the denser parts of blood end up on the outside of the centripete (just because it says "centrifuge" on the outside of the machine doesn't mean that generations of scientists, engineers and aviators knew what they were talking about, children!)

"Ah, but if you cut the string, the stone doesn't fly away from the center!" Oh yes it bloody does. Tangentially, not radially, but still away from the center (assuming that you and I share the definition of "away").

Here's the simple truth

1. A body continues in a straight line unless acted upon by a force.

2. To make a body turn in a circle, you need to apply a force towards the center of the circle

3. Every action provokes an equal and opposite reaction

so the tension pulling the stone inwards is balanced by the force I feel pulling my hand outwards

But ...... and here's a paradox for those interested in such things..... if the inward and outward forces are identical, there is no net force inward, so the stone doesn't move in a circle after all! The inward force must exceed the outward force! Free energy, perpetual motion, collapse of Newtonian physics......

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Physics, Astronomy & Cosmology / Re: What does the term 'time' relate to in time dilation?

« on: 16/12/2018 22:25:37 »

Experience teaches that trying to forge any kind of link between this sort of mathematical concept and the “real world” leads nowhere. 

Far from it. A rigorous treatment of infintesimals leads to differential calculus, whence we get the whole world of classical physics, mesoscopic engineering and just about everything that distinguishes enlightened men from priests, politicians, philosophers and all the other human dross we scientists scrape off our shoes.

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Just Chat! / Re: Do we need a nice guy or an effective one as PM

« on: 16/12/2018 13:22:36 »

The job of  prime minister is exactly what it says: to chair the Cabinet and advise the Head of State. Successive PMs have attempted to behave like presidents, and have indeed been described as "leaders" in the gutter press, largely because modern politicians have chosen to represent their parties rather than their constituents and thus given the PM absolute freedom to declare war or screw up a simple declaration of independence. Her Majesty's Loyal Opposition is nothing of the sort: the easiest way to win the next general election is not to hold the government to account, but to allow the PM to make a complete mess of things.

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Just Chat! / Re: Why should the free world tolerate socialism?

« on: 16/12/2018 13:09:02 »

Successful states that have adopted such dangerous socialist principles as free education for all, free health services, and the occasional public ownership of secondary industries such as railways and electricity, include Norway, Sweden, Denmark, Holland, Belgium, Spain....in fact most European constitutional monarchies, nearly all of which rank very high in citizen happiness surveys. Republics which, according to Fox News and the Presidential Idiot are dangerously socialist include Switzerland,  Iceland and Israel, and they seem to be doing fairly well too.

Also worth noting that the supposed American distatste for free health services only applies to Joe Public. The military and members of Congress have unlimited free healthcare,  just as in proper communist states.

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Physics, Astronomy & Cosmology / Re: Can a wall of mushrooms absorb harmful gamma radiation?

« on: 16/12/2018 12:45:28 »

B₁₀ is a good absorber for thermal neutrons but the product does tend to decay into Li and α-particles, which, added to the inherent chemical toxicity of boron, makes for a fairly unhealthy environment. Not that cadmium is much better.

Part of the art of space exploration (indeed exploration in general) is minimisation and conservation of water supplies, because this essential stuff has a habit of sloshing around (dangerously unbalancing even slow vehicles like fire trucks), freezing, and condensing on everything from beards to electronics. It might nevertheless be possible to construct a space vehicle with ice walls, like a hollow  comet, which I humbly suggest is no more bizarre than one made from horse poo and mushrooms. And whilst we are in the province of Wallace and Gromit, how about cheese?

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Just Chat! / Re: Do we need a nice guy or an effective one as PM

« on: 16/12/2018 10:24:33 »

The election of George W Bush and Donald Trumpf to a position of unaccountable power and authority confirms the unfortunate reality of the American Dream: anyone can get to be president. But at least they give us an approach to absolute zero on a scale of charm and competence, against which you can measure the not-quite-zero value of fools like Reagan and crooks like Nixon.

Leaving aside Washington and Lincoln, on the basis that they were (a) creating something out of nothing and (b) named after English towns, so therefore had an unfair advantage, I chose Roosevelt, Truman and Eisenhower as defining 100 on a scale of effective presidency, and was pleased to discover that https://en.wikipedia.org/wiki/Historical_rankings_of_presidents_of_the_United_States a majority of US schoilars agree with me. Their pedigrees are different: one a career politician properly dedicated to public rather than party service, and two ex-military officers.

Not sure how this can map onto UK prime ministers except to reflect that PMs are not heads of states, are not elected by the public, and do not have presidential powers. But you would probably rank Attlee and Churchill as highly effective, with entirely different backgrounds and talents

In public, Attlee was modest and unassuming; he was ineffective at public relations and lacked charisma. His strengths emerged behind the scenes, especially in committees where his depth of knowledge, quiet demeanour, objectivity, and pragmatism proved decisive.

.


Good subject. I'll think more about it!

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Physics, Astronomy & Cosmology / Re: How viable is Elon Musk's Hyper Loop?

« on: 16/12/2018 08:47:31 »

+0.5g is tolerable to most people for a short period, but -0.5g sustained deceleration is very uncomfortable, often disorientating,  and possibly dangerous to the unfit, hence the need for a tilting seat.