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A weighty and massive subject

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Alan H
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Joined: July 3rd, 2007, 10:26 pm

A weighty and massive subject

#1 Post by Alan H » November 17th, 2007, 11:28 am

Thought this might be interesting...
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The Scotsman - Lightening the load on weighty issue of physics
http://premium.thescotsman.scotsman.com ... tssubscrip
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Lightening the load on weighty issue of physics
CHARLES BUCHAN

I ASSERT that the physics community is never going to convert the mass (sic) of the populace to the physics usage of the weight word.

Linguistically, during the evolution of modern English, the words mass and weight have been synonymous, not only colloquially, but also in learned publications.

However, physics, quite independently, unilaterally redefined "weight" as "a quantity which results from gravitational action".

After spending 39 years earnestly preaching to generations of captive adolescents the essential differences between mass and the gravity force, using at least that number of different methods of explanation, I have suffered a Pauline conversion. My Damascene moment occurred when I was marking a straightforward question addressed to Intermediate level pupils.

Essentially, it asked "what is the weight of a mass of 25kg?"

It will come as little surprise to experienced teachers that about a third of the responses said 25kg and that about another third said 250kg.

Only 5 per cent of the responses gave the correct answer of 250 N.

After firstly banging my head against the nearest mass, (the wall), my response was to ask myself, "Why do I bother?"

I have had successes with the teaching of weight. Unfortunately, these have been limited to the scholastic academics, who can accept anything coming from authority, and the natural physicists, who need few linguistic guidelines to appreciate the fundamental ideas of mass and force. The mass of my pupils, upon whom we also depend for our future, do try hard, and multiply any number with the unit "kg" after it by ten with gusto - but often completely out of the correct context.

My disappointment has been ameliorated by the realisation that this is not a physics problem, nor should it be my problem.

Years and years of usage from outside the physics universe, from the general public, the media, and from mathematicians and chemists (who should perhaps know better), have engendered a climate where the meaning of the word "weight" produces linguistic tension in most of our pupils.

Our poor pupils not only have to cope with the demands of an intellectually rigorous topic, motion, which is full of demanding concepts, but also have to try to model the concept of gravitational force through the fog of obscure and unfortunate nomenclature, after having suffered inculcation from birth with the "commonsense" equivalence of mass and weight.

Yet physics encourages and perpetuates the continuing use of an everyday word for a technically explicit concept, completely at odds with its everyday meaning.

The present English word "weight" derives fairly directly from the old German word wegan, meaning to carry, or convey, and was used often in relation to balances. Up to the end of the 16th century, the word was synonymous with mass.

Galileo, the father of controlled experimental physics, accepted this usage. In his discourse on the nature of motion, De motu, 1590, he persistently uses the old Italian gravita, meaning having gravity, instead of using a term for inertial mass. However, the great man could not be expected to anticipate Newtonian ideas on gravity, and hence the new definition of weight as the force of gravity. With Galileo Galilei, the 10,000-year struggle of civilised man to understand motion had made a quantum leap of progress.

Fourteenth century savants such as the mathematician and theologian Thomas Bradwardine of Oxford, and polymath Nicole Oresme of Paris, had already realised that the theories of the pagan ancients such as Aristotle did not describe reality, but their work on improving the fundamentals of kinematics basically led up a blind alley, having to satisfy elements of metaphysics and theology as well as what we now call physics.

Galileo was the first to see through this fog of obscurity, so let us forgive his imprecision of language at this stage in classical development.

But now, despite another 400 years of usage by the physics community, the word "weight" is no longer fit for purpose; it has failed its 21st century MOT.

Ipso facto, it follows that the solution to the problem is very clear.

Let us consign the W word to the oubliette, to whatever is the physics equivalent of the Vatican's Index Librorum Prohibitorum, (the list of forbidden books). Requiescere in pace - let it rest in peace with other words of the devil such as centi*ugal, suc*, hea* of ovens, siz*, rea*ing, po*ndal, g-*orce and *ig-*ags (known as graphical lines).

We should reject it, ignore it, leave it to the province of the scientific illiterate, to the editors of the national tabloids.

And its replacement?

Our customers appear to like the word "gravity", judging by its frequency of usage.

So would anyone object to "gravity force"?

We seem to have persuaded our pupils fairly easily at SQA Higher Grade to use the idiosyncratic term "buoyancy force", (and even occasionally to spell it correctly).

"Gravity force" is at least accessible and its meaning is unambiguous. Setters of national exams could improve the true assessment of physics, by removing the weighty (sorry) linguistic impedimenta associated with the W word, simply by not using it.

As a Janeite would have it, it is a word lost to respectability; let no decent person have anything more to do with it.

• Charles Buchan is head of physics at Fraserburgh Academy. He has held many SQA posts, including science panel convener and advisory group member, and has had national and regional development roles in Standard Grade and Higher Still. He is a former teacher-researcher in medieval science at New College, University of Oxford.

[Captured: 17 November 2007 11:26:52]

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Nick
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#2 Post by Nick » November 17th, 2007, 2:22 pm

I'm not surprised the poor kids got it wrong (though not perhaps the ones who, for some strange reason, put 250kg) As the piece says, it's a linguistic problem. My particular bugbear is 'light-year', used to describe the passage of time (most notably in a TV commercial for Fairy Liquid) instead of distance. :angry:

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Alan H
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#3 Post by Alan H » November 17th, 2007, 11:47 pm

What other basic scientific facts do the general public usually get wrong?

squiffy
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#4 Post by squiffy » November 18th, 2007, 11:55 am

One which bugs me, but is scientifiic with a more medical leaning is the use of "Cretin" as a synonym for idiot or stupid person.

Cretinism is a disorder brought about by a deficiency of thyroid hormones. It is a congenital disorder, now thankfully rare due to better antenatal care and treatment, and results in mental retardation and restricted physical growth.

It isn't the same as being thick!

Light years is (are?) a pain in the behind too and I'm never sure about electricity travelling along wires or sound waves.

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Alan H
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#5 Post by Alan H » November 18th, 2007, 1:05 pm

squiffy wrote:I'm never sure about electricity travelling along wires or sound waves.
Not sure exactly what you mean, but many get confused with current, voltage and power in electricity. Current is the electricity (electrons) flowing in the wires, pushed along by the voltage. Power is the 'amount' of electricity used and is simply the current multiplied by the voltage. Current is measured in Amps (after André-Marie Ampère), voltage in, well, Volts (after Alessandro Volta) and power in Watts (after James Watt)

For example, a 100 Watt bulb connected to the UK mains voltage, which is 230 Volts, takes about 0.4 Amps. Ohms Law says Power = Voltage times Current. Know any two and you can easily calculate the third.

However, what bugs me is people saying things like 'a power of 230 Volts', or even worse, 'a current of 230 Volts'!

However, it does get confusing because we call the mains AC, meaning 'alternating current' and also apply it to voltage, so you can talk about the mains being '230 Volts AC'! A battery (eg car, torch) is DC, or Direct Current). No wonder people get confused!

Question: at what speed do electrons move through a wire?

Phaedo
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#6 Post by Phaedo » November 18th, 2007, 3:08 pm

Alan H wrote: Question: at what speed do electrons move through a wire?

v = I/nAQ
where
I is the electric current
n is number of charged particles per unit volume
A is the cross-sectional area of the conductor
v is the drift velocity, and
Q is the charge on each particle.
True lovers of knowledge are temperate and brave...
Socrates

tubataxidriver
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#7 Post by tubataxidriver » November 18th, 2007, 3:12 pm

I think one of the common problems with understanding electricity is the difference between the direction of electron flow and the direction of conventional current flow. Current is generally treated as a flow of positive charge, whereas electrons are actually negatively charged, so one is the negative of the other.

This makes a difference when working out the directions of induced magnetic fields from currents in wires (left hand rule, right hand rule), and hence in the direction of a force on a wire in a static magnetic field and hence the direction in which motors turn. I was lucky to be brought up in the era when both were explained. Sadly, I now have to know about this for a living.

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Alan H
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#8 Post by Alan H » November 18th, 2007, 4:03 pm

Phaedo wrote:
Alan H wrote: Question: at what speed do electrons move through a wire?

v = I/nAQ
where
I is the electric current
n is number of charged particles per unit volume
A is the cross-sectional area of the conductor
v is the drift velocity, and
Q is the charge on each particle.
Yes, well...I think the common answer is the speed of light! However, it is 'typically' in the order of a few millimetres a second and many find this surprising. This is the average drift velocity of electrons in the wire, but the effect of a voltage being applied at one end of a wire is felt much more quickly!

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Alan H
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#9 Post by Alan H » November 18th, 2007, 4:10 pm

tubataxidriver wrote:I think one of the common problems with understanding electricity is the difference between the direction of electron flow and the direction of conventional current flow. Current is generally treated as a flow of positive charge, whereas electrons are actually negatively charged, so one is the negative of the other.

This makes a difference when working out the directions of induced magnetic fields from currents in wires (left hand rule, right hand rule), and hence in the direction of a force on a wire in a static magnetic field and hence the direction in which motors turn. I was lucky to be brought up in the era when both were explained. Sadly, I now have to know about this for a living.
While you are absolutely correct, I think the difference is lost on most people! Just try explaining that conventional current flow is actually the movement of 'holes' that go in the opposite direction to electrons!

I once did understand the right and left-hand rules, but I've long forgotten how to use them and strangely, I don't feel the need to re-learn them!

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Alan H
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#10 Post by Alan H » November 20th, 2007, 2:16 pm

Of course, many of the abuses of power, frequency and other such technical terms are the pseudo scientific lot.

For example, see "Colour Bath" by Colour Energies. According to the charlatans who sell this stuff:
...colour is pure energy and... each colour of the rainbow has a different frequency & power which reach you through light rays!
Now, this is partially true, but I still doubt the sellers really know what they're talking about! And anyway, where's the proof that these colours have the effect they claim? And what of 'our body’s seven energy centers (chakras)'? What nonsense!

This is also another example of these people using scientific-sounding words, in this case 'Chromotherapy'. Sounds a bit like chemotherapy, doesn't it?
Alan Henness

There are three fundamental questions for anyone advocating Brexit:

1. What, precisely, are the significant and tangible benefits of leaving the EU?
2. What damage to the UK and its citizens is an acceptable price to pay for those benefits?
3. Which ruling of the ECJ is most persuasive of the need to leave its jurisdiction?

tubataxidriver
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#11 Post by tubataxidriver » November 20th, 2007, 8:54 pm

I was lucky to spend many years working with dye lasers, which produce wonderful monochromatic beams that are finely wavelength tunable in minuscule steps over a wide range of different colours from violet down into deep reds. It's amazing to think that only a few people would have ever seen such pure colours (although they will be present for all to see, lost, within white light). And it's amazing to realise that the human eye / brain can differentiate these very subtly different colours with the primitive 3-colour system making up the retina. It makes my blood boil when I hear nonsense such as "colour therapy" and even the concept of "primary colours". I'm afraid optics is far more complex and beautiful.

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