Category Archives: Physics

Look at the pretty pictures…

Uniformity of practice seldom continues long without good reason.

So opined the estimable Dr Johnson in 1775. In other words, if a thing is done in a certain way, and continues to be done in that same way for a number of years by many different people, then it is a pretty safe bet that there is a good reason for doing the thing that way. And this is true even when that reason is not immediately apparent.

For the choice of this situation there must have been some general reason, which the change of manners has left in obscurity.

— Samuel Johnson, A Journey To The Western Islands of Scotland (1775).

Consider the following examples of “uniformity of practice”:

wp-1487108711715.png

wp-1487109018433.pngexam1

They are fairly bog-standard GCSE examination questions from the last two years from three different exam boards. But compare and contrast with an O-level Physics paper from 1966:

exam2.jpg

exam3.jpg

 

The “uniformity of practice” that leaps out at me is that the more modern papers, as a rule, have many more illustrations than the older paper. Partly, of course, this is to do with technology. It would have been (presumably) vastly more expensive to include illustrations in the 1966 paper.

Even if we assume that the difficulty level of the questions in the modern and older papers are equivalent (and therein lies a really complex argument which I’m not going to get into), there is a vast difference in the norms of presentation. For example, the modern papers seems to eschew large blocks of dense, descriptive text; this extends to presenting the contextual information in the ultrasound question as a labelled diagram.

Now I’m not saying that this is automatically a good or a bad thing, but there does seem to be a notable “uniformity of practice” in the modern papers.

Now what could the “general reason” for this choice?

Rather than leave the “change of manners” responsible for the choice “in obscurity”, I will hazard a guess: the examiners know or suspect that many of their candidates will struggle with reading technical prose at GCSE level, and wish to provide visual cues in order for students to play “guess the context” games.

Now I’m not assigning blame or opprobrium on to the examiners here. If I was asked to design an exam paper for a wide range of abilities I might very well come up with a similar format myself.

But does it matter? Are we testing Physics or reading comprehension here?

My point would be that there can be an elegance and beauty in even the most arid scientific prose. At its best, scientific prose communicates complex ideas simply, accurately and concisely. It may seem sparse and dry at first glance, but that is only because it is designed to be efficient — irrelevancies have been ruthlessly excised. Specialised technical terms are used liberally, of course, but this is only because they serve to simplify rather than complicate the means of expression. 

Sometimes, “everyday language” serves to make communication less direct by reason of vagueness, ambivalence or circumlocution. You might care to read (say) one of Ernest Rutherford’s papers to see what I mean by good scientific prose.

The O-level paper provides, I think, a “beginner’s guide” to the world of scientific, technical prose. Whereas a modern question on falling objects might tack on the sentence “You may ignore the effects of air resistance” as an afterthought or caveat, the O-level paper uses the more concise phrase “a body falling freely” which includes that very concept.

To sum up, my concern is that in seeking to make things easier, we have actually ended up making things harder, and robbing students of an opportunity to experience clear, concise scientific communication.

21 Comments

Filed under Assessment, Education, Physics

IoP Energy: “Store” of Wisdom or Little Shop of Horrors?

“Something with a lot of energy will kill you.”

This has stayed with me from my PGCE course at Swansea University, many years ago. It was said by Frank Banks, the course tutor, in response to the question “What’s the simplest way to describe energy?”

And as pithy descriptions of energy go, it’s not half-bad. A small stone, dropped from the top of a skyscraper: lots of energy before it hits the ground — it could kill you. A grand piano, dropped from six feet above your head: lots of energy — it could kill you. Licking your fingers and touching the bare live and neutral wires in a socket: the conduction electrons in your body suddenly acquire a lot of energy — and yes, they could kill you. (With alternating current, of course, the electrons that will kill you are already inside your body — freaky!)

This attention-grabbing definition of energy seems to lead naturally to a more formal definition of “Energy is the capacity to do work“. This still leaves the problem of defining work, of course, but as R. A. Lafferty once said, that’s another and much more unpleasant story.

As I mentioned in an earlier post, I have been writing the Energy scheme of work for GCSE Science. As part of that brief, I wrote a short summary for my science colleagues of the IoP’s new approach to energy. I present it below without much amendment (or even a proper spellcheck) in the hope that someone, somewhere, at some time — may find it useful  🙂

 

The problem with teaching energy

One reason for the difficulty in deciding what to say about energy at school level is that the scientific idea of energy is very abstract.  It is, for example, impossible to say in simple language what energy is, or means.  Another problem is that the word ‘energy’ has entered everyday discourse, with a meaning that is related to, but very different from, the scientific one. [ . . .]

This ‘forms of energy’ approach has, however, been the subject of much debate. One criticism is that pupils just learn a set of labels, which adds little to their understanding. For example, one current textbook uses the example of a battery powered golf buggy. It asks pupils to think of this in the following terms:

Chemical energy in the battery is transformed into electrical energy which is carried by the wires to the motor. The motor then transforms this into kinetic energy as the buggy moves.

This, however, adds nothing to the following explanation, which does not use energy ideas:

The battery supplies an electric current which makes the motor turn. This then makes the buggy move.

A good general rule when explaining anything is that you should use the smallest number of ideas needed to provide an explanation, and not introduce any that are unnecessary

Robin Millar [2012] http://www.lancsngfl.ac.uk/nationalstrategy/ks3/science/files/TeachingAboutEnergy(RobinMillar).pdf

 

Energy – a new hope (!)

The new approach to the teaching of energy developed by the Institute of Physics (IoP) suggests that we limit our consideration of energy to situations where we might want to do calculations (at KS4, KS5 or beyond).

We should talk of energy being stored and shifted. The emphasis should be on the start and end of the process with minimal attention being given to any intermediate stages.

Consider the following examples:

  • lifting an object. Chemical potential energy store is emptied, and gravitational potential energy store is filled (note that we are not interested in intermediate motion as it doesn’t affect the final energy store).
  • rolling an object down a slope to the bottom. Gravitational potential energy store is emptied and thermal energy stores (of slope, of pen) increased.
  • Boiling water in kettle. Chemical store (from coal/gas power station) is emptied. Thermal store of water increased, thermal store of air increased, thermal store of kettle increased.

[Examples taken from http://scientistshavesaid.blogspot.co.uk/2013/02/teaching-energy.html]

The new approach has been adopted by all UK exam boards for their new specs and is used in the AQA approved textbooks.

The following energy stores are considered: kinetic energy store, gravitational potential energy store, elastic potential energy store, thermal energy store, chemical potential energy store, nuclear energy store, vibrational energy store, electromagnetic energy store (note: the last is limited to situations involving static electric charges and static magnetic poles in magnetic fields).[NB Items in bold are those required for GCSE Combined Science.]

One major difference is that electric current and light are no longer considered as forms of energy. Rather, these are now regarded as means of transferring energy.

 

Rise of the Enojis

enojis

[Image from http://www.supportingphysicsteaching.net/En02PN.html]

I suggest these energy icons should be called enojis (by analogy with emojis).

Probably the biggest adjustment for most teachers will be to avoid referring to light and sound as forms of energy and to treat them as pathways for transferring energy instead.

 

“Energy is the new orange” and summary

More (much more!) on the IoP’s “energy as an orange liquid” model can be found at http://www.supportingphysicsteaching.net/En02TL.html and http://www.supportingphysicsteaching.net/En02PN.html.

enoji2

10 Comments

Filed under Education, Physics, Uncategorized

Songs In The Key Of Energy

​The fact narrated must correspond to something in me to be credible or intelligible. We as we read must become Greeks, Romans, Turks, priest and king, martyr and executioner, must fasten these images to some reality in our secret experience, or we shall learn nothing rightly.

–Ralph Waldo Emerson, “History”

The autumn term is always the longest term: that long drag from the wan sunlight of September to the bleak darkness of December. This is the term that tests both the mettle and the soul of a teacher. At the end of it, many of us have cause to echo the gloom of Francisco’s lines from Hamlet — “’tis bitter cold, and I am sick at heart.”

But even when it seems like it’s all over, it’s still not over. 

The heavy hand of collective-responsibility roulette has tapped me on the shoulder. It’s my turn to write the scheme of work and resources for the next term. I am to write the energy module for the new GCSE Science course. And it must be done, dusted and finished over the Christmas break. The Christmas break.

And the surprising and unexpected truth is . . . I actually think I’m going to like doing it! Yes, really.

Strange to say, I have always enjoyed writing schemes of work. To my mind, it’s a bit like fantasy teaching instead of fantasy football. I move lesson objectives and resources hither and thither where others shift premier league strikers and goalkeepers.

Some aspects of the Science curriculum are abtruse and hard to communicate. Undoubtedly, some of the things we narrate do not always correspond closely enough to something which is already in students to be either credible or intelligible to them. The images and concepts must be fastened to some reality in their “secret experience” for them to learn rightly.

And what can we do to help them? Simply this: make sure that students get as much hands-on practical work as possible. Of course, it goes without saying (I hope!) that it should go hand-in-glove with coherent and thorough explanations of the theoretical underpinnings of scientific understanding.

One without the other is not enough.

Physics: it’s remarkably similar to Maths. But there’s a point to Physics

Let us hope that our students (in the words of R. A. Lafferty) never see a bird fly by without hearing the stuff gurgling in its stomach.

3 Comments

Filed under Education, Physics, Science

The Care And Feeding Of Ripple Tanks (Part One)

And so they’re back — ripple tanks, that is. And a Required Practical to boot!

They were a staple of Physics teaching when I started my career, but somehow they fell into an undeserved desuetude. I know many fine teachers and excellent technicians who have never used one in anger, which is a real pity, since they are a great teaching tool.

So I present here my eclectic mix of ripple tanks: what you really need to know.

The Basics: “Look at the shadows, honey, look at the shadows!”

A ripple tank is simply a container with a transparent base. The idea is to put water in the container and make waves or ripples in the water. A light source is positioned above the water so that a screen underneath the transparent tank is illuminated. The crests and troughs act as converging and diverging lenses and produce a pattern of light and dark lines on the screen which enables us to observe wave behaviour more easily.

Remember: look at the pattern of shadows on the floor or bench top, not the ripple tank itself.

If doing this as a demo, sight lines will usually be a bitch for your class. If you have an old fashioned OHP, just put the tank on top of it and project the shadow pattern on to a wall or screen. Alternatively, experiment with positioning the light source underneath the tank and projecting the pattern on to the ceiling.

“Water, Electricity, Children and Darkness: What Could Possibly Go Wrong?”

The ripple tank works best in subdued lighting conditions. Make sure that walkways are free of bags and other trip hazards. If you want students to complete other work during this time, giving them desk lamps (e.g. the ones used by biologists for microscopes) can be useful, and can actually create a nice atmosphere.

Have some towels ready to mop up any water spills.

Most ripple tanks use a low voltage (12V) bulb and vibration generator (0-3 V) to minimise any electrical hazards involved. Be vigilant when plugging in the low voltage supply to the mains and ensure that the mains cable stays dry.

Fill ‘Er Up!

Have a large plastic beaker handy to fill and drain the ripple tank in situ. Don’t try to fill a ripple tank direct from the tap and carry a filled ripple tank through a “live” classroom — unless you want to risk a Mr Bean-type episode. (But you may need to add more water if demonstrating refraction — just enough to cover the plastic or glass sheet used to change the depth.)

In general, less is more. The ripple tank will be more effective with a very shallow 2-3 mm of water rather than a “deep pan” 2-3 cm.

Use the depth of water as a “spirit level” to get the ripple tank horizontal. Adjust the tank so that the depth of water is uniform. (If this seems low tech, remember that it is likely that ancient Egyptians used a similar technique to ensure a level platform for pyramid building!)

It’s also helpful to try and eliminate surface tension by adding a tiny amount of washing up liquid. I dip the end of a thin wire in a small beaker of detergent and mix thoroughly.

And so it begins…

Before switching on the vibration generator etc., I find it helpful to show what a few simple manually-created waves look like using the tank. Using a dropping pipette to create a few random splashes can be eye catching, and then showing how to create circular and straight wavefronts by tapping rhythmically using  the corner of a ruler and then a straight edge.

5 Comments

Filed under Physics, Science

It’s Not All Relative: Five Things That Einstein Never Said

We have all done it, haven’t we? Each and every one of us has, at some point, appropriated (or misappropriated) a quotation from a great thinker or writer to lend a spurious profundity to our own footling little thoughts.

While it may be well-nigh irresistible to wrap ourselves in the borrowed robes of literary or scientific genius, the temptation is fraught with dangers. To spare both our own blushes and those of our unsuspecting audience, it’s a good idea to check whether the Great Person actually said what they are reputed to have said.

For one reason and another, the life, career and reputation of Albert Einstein makes him an especially tempting target for spurious attributions.

This is my eclectic list of five things that Einstein did NOT say, and yet seem to be quoted and requoted again and again, especially in an educational context.

It is a melancholy truth that these particular memes will most likely be circulating on the internet until the last router rusts away to nothingness. However, on the principle that it better to light a candle than complain about the dark, I present this list (although, given their preternatural persistence, a flamethrower might be more appropriate).

Watch out, any one of them may well be coming to a CPD near you sometime soon…

Nein-stein No. 1

Everyone is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.

This, according to Quote Investigator [QI 1], was first attributed to Einstein as recently as 2004. The original allegory about animals attending a school and being judged against inflexible criteria, can be traced back to physicist Amos E. Dolbear who published it under a pseudonym in 1898.


Nein-stein No. 2

Everything is energy and that’s all there is to it. Match the frequency of the reality you want and you cannot help but get that reality. It can be no other way. This is not philosophy. This is physics.

Philosophy this gem certainly isn’t. Sadly, it bears no relation to any recognisable form of Physics either. (“Pass the bag labeled ‘New Age Quantum Claptrap’ please, Alice.”)

The original form of this quotation was penned by special effects artist Darryl Anka in 1998 — forty years after Einstein had shuffled off this mortal coil (or, at least, had become significantly less ordered).

Incidentally, Anka never attempted to attribute this thought to Einstein. In fact, he claimed that it had been obtained via “trans-dimensional channelling” from an extraterrestrial entity named “Bashar”. [QI 2]


Nein-stein No. 3

Two things inspire me to awe: the starry heavens and the moral universe within.

A beautiful quote, but Einstein? Naaaah. From Immanuel Kant’s Critique of Practical Reason (1788), actually. Highbrow enough for ya? [Ref 1]


Nein-stein No. 4

The definition of insanity is doing the same thing over and over and expecting different results.

Not Einstein. Not Benjamin Franklin. Not Rita Mae Brown either. The earliest instance tracked down by Wikiquote was from a Narcotics Anonymous publication from 1981.


Nein-stein No. 5

Two things are infinite: the universe and human stupidity. Actually, I’m not sure about the universe.

Einstein may or may not have said this, but the only evidence we have is from the works of therapist Frederick S. Perls, who credited the quote to a “great astronomer” in a book published in 1947. In later works, Perls specifically named Einstein as the originator of the quote which was said during a personal meeting with Perls. However, Perls did present different versions of the statement over the years. [QI 3]

3 Comments

Filed under Humour, Physics, Science

The F.B.I. and Gang Signs for Physicists

Those notions which are to be collected by reason . . . will seldom stand forward in the mind, but lie treasured in the remoter repositories of memory, to be found only when they are sought.

— Samuel Johnson, The Rambler, 7 April 1759

Sir John Ambrose Fleming (1849-1945) was the inventor of the thermionic valve, devices that formed the glowing (literally!) and pulsing heart of most electronic circuits until the invention of the transistor in the 1960s and the dawn of the Age of Semiconductors.

His part in most GCSE and A-level courses is small in extent but of significant and perhaps under acknowledged importance: he is the original framer of Fleming’s Left Hand Rule and Fleming’s Right Hand Rule. These respectively predict the direction of the force produced on a current-carrying conductor in a magnetic field (left hand) and the direction of induced current flow when a conductor cuts magnetic field lines (right hand). In short, they summarise the physics of everything from the humble electric motor to the Large Hadron Collider via the rail gun; not to mention the giant spinning generators that produce the humming electrical essence that powers our civilisation.

To use the rules, hold your thumb and first two fingers at right angles to each other. I tell my students that the left hand rule and right hand rule are physicists’ gang sign — it’s not too great a stretch of the imagination, at that. If you have ever invigilated a Physics exam, you can tell the point when the students have reached the Fleming’s Left/Right Hand Rule question . . . just look at their hands!
image

But I digress. I began this post because I was taught the following mnemonic for FLHR:

And to be honest, I have passed it on without thinking too hard about it. However, a student recently introduced me to the F.B.I. Mnemonic. Start with your thumb and say “F for force”, first finger and say “B for B-field” and then second finger and say “I for current”.

The great advantage of this is that F, B and I are the standard physical symbols for the quantities they represent, unlike the multistage hoop-jumping demanded by the traditional mnemonic.

I don’t know about you, but I think I will be using the FBI mnemonic from now on (which, incidentally, was developed by Robert Van De Graaff (1901-1967), of Van De Graaff generator fame).

5 Comments

Filed under Humour, Physics

The Renaming of Parts; or, Energy is the New Orange

image

A PC approach to energy?

Neil Atkin recently wrote a fascinating post about the “New” approach for teaching the concept of energy to secondary school students, and provides some interesting commentary and some very useful links: go read!

I first came across the work of Ogborn and Boohan, on which much of the “New Approach” is based, in the 1990s. I remember embracing it enthusiastically. However, I subsequently returned to the more “traditional” kinetic-chemical-heat-potential-light-sound “naming of parts” model, mostly because many of the resources favoured by our students followed the older convention.

And so it has remained for a number of years, so I was all set to give the “New Approach” a proper rubbishing (as might be gleaned from my selection of the Gary Larson cartoon above) as a specious form of PC — physical correctness as opposed to political correctness, perhaps.

But as I read more about the “New Approach”, I gradually came to the conclusion that it is conceptually sound. More importantly, I think it follows one of the basic principles suggested by Engelmann and Carnine:

[I]f we are to understand how to communicate a particular bit of knowledge . . . we must understand the essential features of the particular concept that we are attempting to convey. Only if we understand what it is and how it differs from related concepts can we design a communication that effectively conveys the concept to the learner.
The Theory Of Instruction, location 296

In other words, I think the “New Approach” is a more accurate representation of the physics of energy, and less likely to lead to misconceptions and false inferences.

Energy Is The New Orange

image

Pure Orange; or energy as a quasi-material entity

Read Dr Dav’s excellent blog post from 2013 for a clear summary of the arguments in favour of the New Approach, as well as Robin Millar’s excellent paper on the topic.

Rise of the Enoji

One of the suggestions made in the IOP’s Energy 11-14 is to use ideograms or icons to represent different energy stores.

image

Rise of the Enojis

By analogy with the ubiquitous ’emojis’ I suggest that we should call these energy icons Enojis. Who knows, it could just catch on…

3 Comments

Filed under Physics, Science, Siegfried Engelmann