Table of contents

YOUR NEWS WANTED The news section gives updates on what has been happening in physics education worldwide. Items included show how events in one country could be relevant to good practice elsewhere in the world. Contributions are welcome from all our readers and should be about 200 to 300 words and can include a picture. Please send your news items for the May issue of Physics Education to ped@iop.org before 19 March 2001.

PHYSICS AT ASEWarm welcome for new-look Physics Education

The new-look Physics Education was successfully launched with a reception at the annual meeting of the Association for Science Education in Guildford. In the exhibition hall the more colourful, user-friendly format proved attractive, not only to the many physics teachers at the conference, but also to general science, biology and chemistry teachers.

'This is really essential stuff for all of us physics teachers' said one delegate, impressed.

Pictured here are Jerry Cowhig, Managing Director of Institute of Physics Publishing, and Andrea Pomroy, Publisher.KP

TEACHING COMMUNITYConference in the Netherlands

For many years about 400 physics teachers from the Netherlands have gathered near Amsterdam for a two-day conference. This year the plenary lectures were on String Theory, bringing teachers up to date with the frontiers of subject knowledge; and the UK Advancing Physics project showing a significant curriculum development. The workshop sessions saw many presentations on the use of software in modelling physics to help student understanding. Interactive Physics and Crocodile clips were both shown by teachers who use them in their schools. There were also discussions about how to introduce fundamental physics ideas into the curriculum.

As well as a chance for professional development the meeting is a significant social occasion with old friendships renewed and new ones made. The major manufacturers and publishers all attend a market after the evening sessions and delegates look at new products over a cup of coffee or a glass of beer. The conference ended by proving physics teachers are really just grown up children as the whole conference enjoyed a presentation from the London Science Museum on Blowing Bubbles, which is really intended for seven-year olds.

Bubbles attract an audience.PB

RESEARCHEvidence based practice

This three-year research programme aims to explore the relationship between research and practice in education. There are four projects. One will look at how diagnostic tools used in research can be further developed to improve science learning in normal classroom teaching. Another will look at why teachers do take on board some research based evidence about teaching and learning but ignore other published findings. The third project looks at what should be taught to pupils about what science is and how. Finally, there is a project which investigates the influence of educational research. All potential users of research will be asked if they see it as useful and relevant.

More details can be found at http://www.york.ac.uk/depts/educ/projs/EPSEPB

PHYSICS AT ASETeacher of Physics Awards

'I would like to nominate my physics teacher for your award. If he had not come to school when I started the sixth form I would not be studying physics now.'

This year the Institute of Physics has awarded eight people its prestigious Teacher of Physics Award. There can be few more rewarding things than to be put forward for a teaching award by a former pupil, and that is the case for many of the recipients. The awards, which are not competitive, recognize good classroom teaching which has inspired students. Sometimes it is actively engaging in physics by taking them out of school to lectures and visits; sometimes it is exciting project work in school. But it always comes back to inspiration in the classroom in everyday school physics lessons.

This year's winners are:

• David Nixon, Brooksbank School, Leeds

• Mike Rutland, George Abbot School, Guildford

• David Smith, Greensward College, Hockley, Essex

• Helen Pollard, Kings School, Peterborough

• Philip Britton, Leeds Grammar School, Leeds

• Simon Carson, Norton College, Malton, North Yorkshire

• Tony Ward, Sandown High School, Isle of Wight

• David Hall, Whitby County High School, Ellesmere Port, Cheshire

Each year the Institute seeks to highlight outstanding teachers and a panel sits every December to decide the winners. The more excellent teachers we hear about the more awards we are able to give. If you know of someone who you think fits the bill of being an outstanding classroom teacher of physics then we would like to hear from you. For more details and a nomination form, please contact Ian Cuthbert, Institute of Physics, 76 Portland Place, London, W1B 1NT ian.Cuthbert@iop.org.

Mike Rutland with some of his pupils at George Abbot School, Guildford

Steven Chapman

PHYSICS AT ASEFestival encourages science teachers

Yes - you're special, you teach science! You are part of a great tradition. The classrooms, the facilities, the hairstyles and the equipment may have changed, but our general good intent remains.

Celebrating 100 years of the UK's Association for Science Education, The Science Teacher Festival which took place at the ASE conference in Guildford, UK, in January was a treasure-trove of artefacts: there were photos, teaching schemes, videos, books and equipment dating from the early 1900s up until the present day. It was a chance for 'mature' teachers to look back nostalgically and for us all to be inspired by the wisdom, dedication and creativity of earlier generations. But, as Mick Nott, festival organizer, pointed out: the most important outcome from the event was to make science teachers realize that they are very important and very special people. And it's refreshing when you hear that message.

Simon Winslow (Two Trees High School, Manchester) and Jo Davies (Castle Hall School, Mirfield) enjoy the display at the Science Teacher Festival.KP

AWARDSBragg Medal

The Institute of Physics Bragg medal is awarded for outstanding contributions to Physics Education. This years the award has gone to Professor George Marx. George Marx is a distinguished nuclear and particle physicist. He and his student Sandor Szalay were the first to propose the possibility that if the neutrino had mass it would account for the 'missing mass' in the Universe.

President of the Roland Eötvös Physical Society and Professor and head of Department in the Roland Eötvös University Budapest, from the earliest stages he took an active interest in developments in physics education. Starting in the 1960s he organized a series of Danube seminars which brought physics teachers from Hungary, the then Yugoslavia and Czechoslovakia, Poland, East Germany and Russia together with leading figures from the West, including those on the Nuffield projects. These seminars amongst other things led to a complete revision of the Hungarian physics curriculum, adapting and in many cases improving on ideas from Nuffield and PSSC. He was influential in seeing that the new textbooks written for the course were of the highest standard and kept alive the freshness of the ideas he and others had developed.

It can fairly be said that through the Danube Seminars and later work as President of Girep, George Marx brought into existence the now very strong Eastern European community of physics educators. He worked closely with Abdus Salam's Centre for Theoretical Physics in Trieste on its international education programmes, leading teams to Sudan, Kenya and other third world countries. He developed good relations between Hungary and China in physics education, at a time when few other countries had access to China, and was influential in moving Chinese thinking forward.

George MarxPB

PHYSICS AT ASEMeteorites are cool!

Monica Grady displays priceless meteorites

Stories of white hot meteorites blasting to the ground and setting fire to barns and haystacks are unfounded. The audience of the 2001 Physics Education lecture were generally surprised when Dr Monica Grady, Curator of Meteorites at the London's Natural History Museum, explained how meteorites heat rapidly due to their high velocity as they enter Earth's atmosphere, but, by the time they land, have slowed down and therefore cooled.

Monica Grady, an internationally renowned meteorite expert, is currently highly sought-after by the science media because of a resurge of interest in the Martian meteorites which, in 1996, NASA claimed may contain evidence of life. Grady's view is that if there are bacteria in a metorite they are almost certainly contaminants from Earth. Meteorites enter Earth's atmosphere from the vacuum of space, so air will enter any spaces within the rock. There are many ways in which even the most carefully collected meteorite could be exposed to terrestrial bacteria. So, how can we be sure about life on Mars? If we want to be sure, we have to go there. Exciting stuff. KP

PUBLIC UNDERSTANDINGMarch 2001 - a science odyssey

From 16-25 March, National Science Week will involve over a million people in all manner of science events throughout the UK. Many events will be based at schools and universities. But shopping centres, disused railway stations, art galleries, pubs and bars will all host different activities, debates, competitions and demonstrations. Exploding custard and Jurassic Jellies will entertain and inspire young people in London at the annual BAYSday (British Association of Young Scientists). In Halifax there will be a sleepover at the Eureka Science Centre. Delegates at the IoP Congress in Brighton will enjoy a lecture on the Physics of Juggling that explains the complex patterns involved.

The full programme of events is available on the internet at www.britassoc.org.ukPB

WEB RESOURCESNew website launched to support the gifted and talented

Eighteen months ago, the UK's Department for Education and Employment launched an initiative called Excellence in Cities to improve standards in urban schools in England.

One strand of this policy requires schools in these areas to provide distinctive teaching and learning programmes and extracurricular activities for their top 10% of students. This is irrespective of whether the school is comprehensive (all ability) or selective. The intention is to focus attention on school self-evaluation so that the school's best students are given opportunities to do even better.

When the programme's co-ordinators were being trained last year, they identified a crucial need for curriculum specific information so that they could do their jobs of supporting school colleagues to devise distinctive programmes to stretch able students in their respective subjects.

In response to this, the 'Xcalibre project' was launched. Xcalibre will develop a website to provide a directory of resources that enrich the curriculum within and outside school. It will give details of schemes of work that challenge the able by providing a deeper dimension to lessons. There will be a chance to post reviews of those resources on the website. There will also be a bulletin board to promote collaboration across subject or geographical boundaries on projects and reflection upon research findings.

Interested parties are invited to recommend high calibre proven resources that have enthused able young people of all ages from 5 to post-16.

Xcalibre aims to be a site that stimulates cross-curricular and transnational work. Contributions will be warmly welcomed from teachers, researchers, consultants or organizations concerned with transferring the skills and knowledge of your subject to intriguing challenges in other curriculum areas as well as all those involved in enrichment activities within your own subject.

If you would like to be involved in this venture please contact:

Patricia MacLachlanE-mail: mpm@cam.ac.uk Tel: +44 (0) 1223 472600

PHYSICS TEACHINGA Fun lesson

One of the delights of the ptnc news and comment e-mail network for physics teachers is the wide range of topics that appear, from serious educational debate to discussion of physics concepts, and from matters of departmental organization to curriculum development. In the days before Christmas Mike Bell asked if anyone had any ideas for a fun end-of-term lesson. He got four replies showing just what teachers get up to in those final days of term...!

• Ian Yorston, Head of Science at Radley College, suggested some festive reading: 'Physics of Christmas by Roger Highfield covers most things! Physics of Star Trek by Lawrence Krauss should cover the rest.'

• Professor Varma had a practical idea: 'Have them make paper planes and end up with a paper plane flying competition.'

• Simon Petts suggested: 'Try a physics quiz, Physics hangman or Physics Pictionary.'

• Marc Bloch suggested a useful website: 'May I recommend some of the fun lesson ideas from the Harvard Hot Air site http://www.improbable.com/ The site includes all relevant references to the data.'

Mike Bell acted on the advice: 'I tried science Pictionary using a set of cards quickly made from unit key words - it went down well and we had more fun than those who chose videos.'

To subscribe to ptnc e-mail listserve@networks.iop.org. Don't fill the subject line but write SUBSCRIBE PTNC in the e-mail message itself. Your subscription will also be confirmed by e-mail.

RESEARCH FRONTIERSAre cell phones safe?

Some UK schools have recently found an easy way to make money - they can collect good rent by allowing cell phone companies to put radio masts on the school roof. But many parents are worried that the radio waves are bad for the health of their children. Many teenagers seem to spend most of their life holding a cell phone. What does this do to their brains?

Dr Michael Clark of the UK's National Radiological Protection Board routinely checks radio masks. Cell phones broadcast at frequencies of about 2 GHz (depending on the phone company). The internationally agreed basic restriction (below which there are no detectable effects on living organisms) is 2 W kg^-1.

At ground level the signal is always many thousands of times less than this.

Radio waves are emitted from the masts along a fairly narrow angle so that if you were stood close under a radio mast you would receive virtually no signal directly from the mast. Only when you travel a few hundred metres from the mast is the direct signal significant.

So what is the health risk? The report Mobile Phones and Health, produced by the Independent Expert Group on Mobiles Phones, chaired by Sir William Stewart in April 2000, found that lack of information and lack of planning control caused real worries and annoyance which, being stressful, were a risk to people living near transmitters.

With millions of people now using cell phones on a daily basis we should be nothing but extremely cautious. There is still no evidence that radio waves, even from continuous use of a mobile phone, would pose a health risk. Traffic accidents (due to inattention) and plane crashes (due to interference) maybe - but the actual radio wave intensity is still below the base level. Hands-free kits halve this again.

Dr Michael Clark of the UK's NRPB using his mobile phone.

Further information: http://www.nrpb.org.uk

OBITUARYRoy Schofield 1924-2000

Roy, who has died recently, was Editor of Physics Education from 1977 to 1980. He was a person of talent and charm who gave much to Physics Education.

During the war, Roy served in the navy, one of his last tasks being to help the Free French with radar on board the improbably named L'Escargot! After studying at University College London, he taught physics in south-east London schools, Colfe's Grammar School and Forest Hill. In 1966 he was appointed physics tutor in the department of education of Brunel University and many former students are grateful for his patience, encouragement and kindness.

As head of department, Roy over-saw the demise of his department in the late eighties. With his courtesy, clarity of thought and courage, he was ideal for mounting the damage-limitation exercise this turned out to be. I remember his telling me with typical wry humour: 'I managed to bring a few gold bars from the wreck but sunk it has.'

Roy was an independent contributor to many curriculum projects and other initiatives, ready to help more as a very constructive critic than as an insider. Nothing sloppy or misconceived was likely to escape his notice but his comments would be gentle and humorous. Throughout his career he remained interested in physics and kept up with the latest developments; the interest in and considerable knowledge of the social sciences relevant to an education lecturer was an add-on not a substitution.

In retirement he helped his wife, Beta, with the revision of various Nuffield Science Project texts. He was also able to follow another interest, philosophy: a fellow pupil at an adult-education class told me that his glosses on what the lecturer said made all clear; this is characteristic of him and I am certain that they were made with the greatest tact.

After Beta's untimely death Roy's life was increasingly restricted by symptoms of Parkinsonism and so he invested in satellite television and a better computer. Thus he was able to watch sport, often accompanied by a member of his family, which was devoted to him, and surf the net. He introduced me to it, showing me pictures taken by the Hubble telescope and his contribution to chat-room debates on philosophy of science. I always came away from visits to him heartened.

David Tawney

Virtual reality - whose reality?

There is an old joke about a farmer who wanted to improve his milk yields and employed an engineer, a psychologist and a physicist to make suggestions. They all went away for a month and came back with their proposals.

The engineer had measured the size of the milking stalls, the ambient temperature and the milking process. She suggested a modest rise in ambient temperature and an alteration in the pumping equipment.

The psychologist decided to paint the stalls green and play a tape-recording of birdsong to the cows to make them feel more content and release their milk more easily. The physicist explained that he had decided to look at things more fundamentally: 'Let us assume that the cow is a sphere' ... he began. And that's the joke.

Some people think that this is the funniest thing out - a physicist can't recognize a cow when they see one. What troubles me is that I didn't get the joke straight away. I am so used to the language and the often-ludicrous assumptions in physics that it did not seem particularly strange or funny. What did you think?

The joke, for me, illustrates the essence of our problem in physics teaching. In a very real way, physics is about another world. It isn't about the real world in which ordinary people live, and they know it. Physics has its own language, its own laws and its own values.

Depleted uranium has been in the news of late. It is interesting to compare the casual way in which physics teachers have discussed the possibilitiy that one atom of uranium can kill someone with the shock-horror reporting of this fact in the press. We are caricatured, sometimes for good reason, being callous, calculating, cold people - out of touch with the things that really matter.

And then there's that other 'real world' - of really tough people who make serious money. Our friends who work out in the worlds of commerce and industry like to mutter, with some superiority, that teachers would never survive in the real world.

So here we are, buffered from the 'reality' of commerce by kind managers, left to teach equations at the expense of moral standards ... Excuse me! Physics is the only subject that confronts real reality head on. Physics is all about how this world, this Universe, this reality works. Moral laws, government legislation and theories of economics are all well, and sometimes good, but they take place within this space we call Our Universe.

Physics is real This issue of Physics Education contains lots of excellent suggestions for practical work - demonstrations of what happens, and suggestions for investigations. I hope that readers will find them useful and maybe share some good ideas of their own. We are dealing with stuff that actually happens, and that is what makes physics both significant and attractive.

The joke I really hate runs 'If it moves it's biology, if it smells it's chemistry and if it doesn't work it's physics'. This is rubbish: gravity always works, in my experience, physics never gets it wrong. In the classroom, maybe a piece of equipment is broken, or the technician forgot the batteries, but we can never say truthfully that 'the experiment didn't work'.

Virtual physics Last week a school governor challenged me to justify the cost of so much laboratory space and equipment when, nowadays, so much can be done using computers. Probably the best 'virtual physics' currently available is on CD-ROM. In this issue of Physics Education we have concentrated on CDs for our review section. There is lots of good material out there which can enhance our teaching with wonderful images, immediate feedback for students, and the possibility of continuously monitored differentiated work but, as I explained to the governor, I don't want to teach virtual physics - physics is very firmly, fairly and squarely in this real world (which may, of course, approximate to a sphere ... .).

Editor Dr Kerry Parker

A simple homemade microscope has been devised using a single water droplet lens, which proved to be practical for classroom use in school. In order to prevent evaporation of water, the water droplet lens was encapsulated in a plastic vessel together with wetted paper. By changing the amount of water in a metal ring (4.5 mm diameter with thickness 0.6 mm) attached to the bottom of the plastic vessel, the magnification could be varied from around ×6 to ×30. It was also demonstrated that microphotographs could be taken readily using an ordinary compact camera. This microscope is expected to make a significant contribution to science education in developing countries.

We examine the structure of five Chinese magic mirror replicas using a special imaging technique developed by the authors. All mirrors are found to have a two-layered structure. The reflecting surface that gives rise to a projected magic pattern on the screen is hidden under a polished half-reflecting top layer. An alternative method of making the magic mirror using ancient technology has been proposed. Finally, we suggest a simple method of reconstructing a mirror replica in the laboratory.

This article describes a simple experimental demonstration of chaotic behaviour produced by driving a spherical pendulum at a frequency very close to its natural frequency.

It is shown how the diameter of the jet of water exiting a hole near the base of a cylindrical container can be determined without knowing the total drain time. The contraction coefficient can be found from two measurements of the speed of the jet - one obtained from conservation of mass and the other by using projectile motion.

Presented here is an easily constructed test circuit assembly for demonstrating the use of an LCR meter to measure equivalent circuit parameters.

Audio signals can be used to modulate the intensity of light emitted by an LED. When this light falls on a photoconducting cell, the change in resistance follow the variations of the audio signal. The variation in this resistance can be employed to control the gain of an amplifier. This article describes an IC circuit producing low-level generation of AM signals using a conventional inverting amplifier configuration where the input signal is the carrier wave and a LDR controls the gain.

An approach to incorporate active learning strategies into the first semester of a university-level introductory physics course is described. Cooperative and peer-based methods inside the classroom are combined with project-based learning outside the classroom in an attempt to develop students' transferable skills in addition to improving their understanding of physics. Initial experiences and lessons learned are described.

The need for pupils to practise significant aspects of scientific work such as the taking of epistemic (related to the nature and construction of knowledge) and methodological decisions is advocated. This requires that they work on problems and activities presented in a more open way than is usual. A case study is discussed.

Physics problems presented by teachers or in textbooks are usually quantitative and offer only one solution. This article suggests that getting students to solve qualitative problems and confronting them with multiple solutions can help them develop conceptual understanding and robust problem-solving strategies.

A form of dimensional analysis based on a pack of cards is described for use with students aged 11-16. This gives new approaches in understanding the manipulation of simple equations, and also aids familiarization with the units involved and the relationships between them. Differentiation is provided by altering the layout of the cards and varying the complexity of the tasks.

The text of the article is available in the PDF.

How and why we teach

An interview with Mick Nott conducted by David Sang

Mick Nott teaches at Sheffield Hallam University. He is editor of School Science Review, and over the last three years he has been organizing a website, book and display for the ASE's Science Teacher Festival.

Mick Nott

You studied Logic with Physics as your undergraduate degree course, at Sussex, at the end of the 1960s. Wasn't this a rather unusual choice? At school, I loved chemistry, particularly physical chemistry. However, physical chemistry didn't love me when I studied it at university. I grew resentful of the demands made on me with the overcrowded morning lecture programme that was mainly a board-copying exercise and the afternoon hours of labs. I felt stifled; there didn't seem to be any space to express oneself. I wanted a course that allowed me some freedom of thought. So in the summer of 1969 I transferred to the Logic with Physics course. Alongside our 'straight' physics we studied the history of topics like atomic and quantum theory, thermodynamics, mechanics from the Greeks to the Newtonian synthesis and we also had a couple of units in the sociology of science.

Amongst the set texts of our first class in the summer of 1969 was Thomas Kuhn's The Structure of Scientific Revolutions. Now well worn with its cover repaired by sticky tape, it still rests on my bookshelves. Reading Kuhn, I understood why I had been dissatisfied with my chemistry course. If I wanted to make it in chemistry I was going to have to conform to thinking exactly like all the other chemists. That wasn't for me.

What attracted you into teaching? And where did you teach? I think it was a vocation in that, from the age of 15, I could imagine myself in the role and it was a job I could 'see' myself doing. Now thinking back I suppose it was an obvious way in which a working class child could transcend class barriers.

I did my postgraduate teacher training at Sussex because it was assessed by coursework and classroom competence (in the early 1970s most such courses still had written examinations). I thought it was fantastic. We spent three days a week from October to May in one school. I had one regular third-year class every week and the rest of my teaching timetable varied from term to term. It was like being a 0.3/0.4 member of staff and for that one third-year class I had to do parents' evenings, reports etc. The teachers were paid to act as tutors for the preparation of schemes of work, lessons and tutorial work and they assessed my teaching. Teachers, tutors and trainees attended seminars together.

My first teaching job was at Holland Park School in London, at a time when it was famous, perhaps even infamous! It was a real baptism of fire - over 2000 pupils, tens of different first languages, a real mix of class and ethnicity, and newly introduced mixed ability teaching for the first three years. We worked very hard writing schemes of work and developing worksheets and audiovisual materials but, on reflection, I am not sure that we were that effective in developing the science curriculum. I remember using Nuffield Combined Science with the first two years and that was in danger of becoming death by a thousand worksheets.

After three years I went to teach in a small private school in Madrid for a year. I was the physics department and my title of Head of Physics meant I was in charge of myself. This was highly formative as a teacher - I had nobody to ask if I didn't understand some physics. As the school was poorly equipped I learned to make apparatus and be very resourceful. There was no pupils' practical work in school science in Spain at that time and I spent a lot of time in hardware stores and medical suppliers!

After Spain all of my teaching career was in 11-18 mixed comprehensives, in Cheshire and then Peterborough, and I rose to the dizzy heights of Head of Science. By the time I left the school in Peterborough in 1986 we had established the curriculum framework for broad and balanced science for all to age 16.

Did your undergraduate studies influence the way you taught science? I think they made me think critically about my teaching right from the start. Although there was much that I admired in the Nuffield approach, I felt that it was unrealistic to expect pupils to discover the whole of Physics for themselves in the time available! In 1973, 'Learning by discovery' was the slogan. My first lesson on my own was with a class of 32 children and 16 brightly illuminated ripple tanks in a dim laboratory. The pupils' task was to 'discover' that v = fλ. The familiar cry, 'What's supposed to happen, Sir?' arose around the room. At the end, as I removed the crocodile clips the pupils had stuck on my jacket, I had to tell them what the result should have been.

Nowadays I am convinced that science has to be taught as well as it has to be learned. I don't go along with the teacher as solely a 'facilitator' of learning and the learning environment. Schooling is an enculturation into ways of thinking and important things to know. Teachers have a responsibility to set an agenda for their pupils, e.g. what is important for pupils to learn, why is it important and how does it contribute pupils' personal and social development as well as their potential development as a scientist.

You played a big role in the Secondary Science Curriculum Review (SSCR) in the 1980s. What impact did that experience have on you? The SSCR started off as a democratic experiment, trying to 'hand' science curriculum development to class teachers. I worked for the project as an advisory teacher for a year developing problem-solving as a teaching strategy in lower secondary school science. I think the SSCR was crucial to the successful launching of broad and balanced science and the political battle to establish science as a core subject.

Can you still discern the influence of the SSCR in today's National Curriculum?I don't think the present science curriculum is what the SSCR envisaged. However, many projects which were partly products of SSCR have had a profound impact (for example the CLIS project Suffolk Coordinated Science and NEAB Modular Science).

I welcomed the inclusion of an attainment target on the nature of science (AT17) in the first version of the National Curriculum but it soon became weakened when the Science National Curriculum was revised. However, I think that some aspects have resurfaced in the new emphasis on ideas and evidence. I was involved in the writing of the Nuffield report, Beyond 2000: Science education for the future, and I think this has had an impact at the policy level, but its suggested strategies were not 'periphery to centre' which was the slogan of the SSCR.

At Sheffield Hallam University, you have been involved in initial teacher training and you have also taught on undergraduate physics courses. What are your areas of interest in teaching and research today? I am interested in the history and culture of science education: Why do we teach science in the way we do? What are the roots of today's science curriculum? Knowing what we know about the past, how can we develop things in the future?

You are now organizing the Science Teacher Festival, celebrating 100 years of the ASE and its forerunners. What made you think this was worth doing? There is an old saying that if we forget our history, we will be condemned to relive it, and I think it was Marx who said that there is no point in studying your past if you are not going to use it to change the future. Looking back through past decades of School Science Review, Physics Education and other journals, you can see the same arguments arising time and again - for example, can pupils learn their science through discovery/problem-solving/investigations? what methods of assessment match our science teaching objectives? should science be taught as general/integrated/separate sciences? These arguments have been with us throughout the past century and the 'winners' and 'losers' rise and fall! I think that to be a profession, we need to recognize our heritage and tradition. At the moment I get the impression that every year is Year Zero as some 'new' initiative starts. We can learn from the past, and next time we try an idea we should take it further, research it deeper and disseminate it wider than we did before.

The text of the article is available in the PDF.

The Editor welcomes letters, by e-mail to ped@iop.org or by post to Dirac House, Temple Back, Bristol BS1 6BE

Force on a pendulum

The simple pendulum has been used by several educationalists for investigating the patterns of thinking among students and their observations that Aristotelian thinking persists among students at college level. I had also considered the simple pendulum in my 1985 letter in Physics Today [1], so I was interested to read the test given by Lenka Czudková and Jana Musilová [2]. When students were asked to draw net forces acting on the particle at various positions, 31.9% of students believed that the net force was tangential to the particle's path the whole time.

To me this is no surprise because in our derivation of the equation for the period of a simple pendulum we assume that the unbalanced sine component provides the restoring force for the harmonic motion of the bob. Of course, Czudková and Musilová's question asked students for the net force on the particle, not the component. The student's answer fits well with the logic of the equilibrium of forces and the parallelogram law.

Lastly, let me bring out the similarity between the student's answer and the thinking of George Gamow. He used to call positrons 'donkey' electrons because of their displacement against the applied force, before Paul Dirac termed them positrons. Victor Weisskeptf told me this anecdote in a letter in May 1982.

References[1] Sathe D 1985 Phys. Today38 144 [2] Czudková L and Musilová J 2000 Phys. Educ.35 428

Dileep V SatheDadawala Jr College, Pune, India

Sound slows down

Without wanting to stir up more trouble amongst the already muddy waters of Physics teaching, consider how many times you have heard (or, more worryingly, read) this:

'Sound waves travel faster in a denser material'

But...The velocity of simple longitudinal waves in a bulk medium is given by v = (K/ρ)^1/2 where K is the bulk modulus and ρ is the density. Note that the speed is inversely proportional to the square root of the density. The higher the density the lower the speed. A little reasoning will lead to the obvious fact that if a material is more dense, then the mass per unit volume is obviously greater, which implies that the acceleration of any part of the material under application of a force will be less than in a lower density material. In addition, the force producing this acceleration will be due to the stiffness quality of the material. The greater the stiffness the larger the force. How the gross error stated above has found its way into elementary physics texts is beyond me. Perhaps it may have something to do with the Earth and atmosphere modules that seem to be 'hot' topics at the moment, rather than a simple application of Newton II.

What amazes me is that if one takes lead and aluminium (not the most uncommon of materials), we find that v_Al ≈ 5000 m s^-1 andv_lead ≈ 2000 m s^-1. Yet lead is about four times as dense as aluminium! (Who is vetting these books, or is the National Curriculum ignorant of the real world?)

Whilst on this subject it seems apparently obvious that a liquid cannot withstand a shear force (it collapses), which is why transverse waves do not travel through the liquid core. Is this simple explanation mentioned? However, in the solid region v = (G/ρ)^1/2 where G is the shear modulus - which accounts for the velocity difference compared with compression waves.

John SevernGeorge Abbot School, Surrey, UK

Bond is back

Further to recent correspondence, it is always better for Bond to throw away both of his shoes at once. This will give him maximum velocity on the frictionless ice. Throwing the shoes separately will never match it. This assumes that each shoe is thrown with identical, maximum, effort in either situation.

Edmonds [1] is correct to surmise, 'These subtle differences must come from momentum being linearly related to the speed and energy being related to the speed squared.'

Oliver Linton [2] 'proved' the opposite. Starting with the maximum effort per throw condition, he wrongly states: 'What this means in practice is that every time Bond throws away a shoe, the separation velocity of the man and shoe is constant,v_sep.' This is not correct! The mass of one object (Bond) is less for the second throw. If energy and momentum are conserved then v_sep will be greater for the second throw.

Consider a general throw (let M and m be the masses of Bond and projectile respectively, V and v their recoil velocities and E the energy transferred from Bond's muscles ('work done') in a single throw):

General caseMomentum: MV = mv, hence: v² = (MV/m)²Energy: E = ½MV² + ½mv²2E = MV² + m(MV/m)² where R =M/m, and by symmetry.

V_sep = V + v (in magnitude)

Now consider two cases:

Case 1: Very massive Bond: M >> mR is very large so [the first term for v_sep] ≈ 0. In the second term: 1+1/R ≈ 1. This gives: v_sep ≈v ≈ (2E/m)^1/2

Case 2: Very low mass Bond: M = mR = 1, both terms are identical and v_sep = 2(E/m)^1/2Note:v_sep is a factor of surd2 larger for the low mass Bond. In generalv_sep is not constant if the M:m ratio can change.

I concentrated on Bond's final velocity and derived an expression forV_S/V_B (B = 'both together', S = 'separate throws'). (For a fuller account of the algebra e-mail me!)

Case 'B' The same as the 'General case', but replace E by 2E(uses two arms), m by 2m and V by V_B:

Case 'S' 1st throw: U = velocity of Bond and remaining shoe in the 'Ice Frame' after throw.

(As for Case 'B' but replacing M by (M + m), 2m by mand 2E by just E.)

2nd throw: Start by finding V_CM (recoil velocity of Bond) in the centre of mass (CM) frame (which has a velocity, U, in the 'Ice Frame').

(Again use Case 'B' by just replacing 2E by E and 2m by m.) V_S = V_CM + U (transforming from CM to Ice Frame)

Final result (after 'a bit' of algebra!)V_S/V_B = (1/surd2) (1+R/2)^1/2 × [(1+R)^-1/2 + (3+2/R+R)^-1/2] This result is not very illuminating unless we try a few examples: (a) M = m (heavy shoes!) so R = 1: ∴ V_S/V_B = 0.966. (b) M = 75 kg and m = 0.5 kg (sensible values), so R =150: V_S/V_B = 0.999994517.

ConclusionsEdmonds is correct. He rightly concluded that the only way to match the recoil velocity of the pair of shoes is to arrange for the shoe velocities in the separate throws to be the same (in the Ice Frame) as the pair of shoes. This is why he invoked the 'extra effort' idea that Oliver Linton and I dismissed. However, he points out that if this is not available then Bond's velocity will be less if he throws separately.

Application to rocket propulsionSome of Oliver Linton's statements about the 'well known' formula for rocket propulsion are also incorrect. The separation speed of fuel and rocket,v_s, is assumed to be constant in the equation - which for a normal rocket is a very good approximation because at any instant the mass of ejected fuel is always much smaller than the mass of rocket and remaining fuel (if any). This is analogous to my 'Case 1' where v_s = v_sep ≈ (2E/m)^1/2 and m Less then M.

Oliver Linton's example of ejecting all the fuel at once from a rocket in which m =M is just my 'Case 2'. The separation velocity here is v_all. It was noted after 'Case 2' that v_all = surd2 v_sep

The rocket formula (gradual release of fuel) V = v_sln[(M +m)/M] gives V = ln2 v_s = 0.693v_sep (using the v_s from Case 1).

But when all the mass is ejected at once we now have (besides a 'bomb'!): V = ½v_all = ½ (surd2 v_sep) = 0.707 v_sepand not the 0.5 v_sep (or '50%') quoted by Oliver Linton.

The reasons why rockets are designed to operate to give this lower theoretical maximum speed are numerous but mainly revolve around not killing the astronauts, not destroying the rocket or reducing drag at lift-off.

References[1] Edmonds J D 2000 Phys. Educ.35 225 [2] Linton J O 2000 Phys. Educ.35 317-8

Laurence CavesBlessed George Napier RC School Addison Road, Banbury OX16 9DG, UK LCaves@blessed-george-napier.oxon.sch.uk

What are you thinking about?

There is a crisis in recruiting physics teachers throughout Northern Europe. Detailed research has shown that the problem may be one of image. It seems that being a teacher is seen as something slightly strange. So is being a physicist. This makes anyone who is a physics teacher (strange)². This effect becomes overwhelming when more than one physics teacher is present, making attendance at gatherings of physics teachers almost unthinkable for the average person. So just what is it that sets physicists aside from the rest of the population? Why do they think we are so strange?

Clearly it is how we think about things. We enter a room and estimate its volume. We visit the fairground and we wonder about the g force. At a football match we estimate the size of the crowd. At sunset we see scattering and at the beach, as the sun glints off the clear water, we think about Brewster's angle, and we estimate the number of pebbles on the beach. We find potential visits and lesson-material at hospitals, concerts, restaurants and on every possible mode of transport. Thinking about things like that is what makes us physics teachers.

Surely everyone has seen The Wizard of Oz. I want you to imagine that you are watching it along with some friends who are not physics teachers. Let's see what they are all thinking about. One is a Roads Engineer. What a state the yellow brick road is in! As the major route in the country of Oz it obviously needs an upgrade. A nice black tarmac surface, some road markings and lighting at the major intersections. There is something else wrong. Dorothy, the Tin man, Scarecrow and Lion are just walking along. Where are the road works, traffic jams and hold-ups? Another friend is a school principal. What an amazing leadership style the Wizard has. Perhaps it would work at school? Those munchkins run around a bit though. There would be a need for some rules about how to play in the playground. Perhaps if the mayor of the Munchkins were to be on performance related pay things might improve? And what are you thinking? What is the conductance of the Tin man? Would it vary measured from head to toe or hand to hand? Students could do extended investigations into the conductance of different body parts. There are surely some great opportunities for projects and science fairs. Students could investigate the suitability of different materials for making Tin man suits. They could do a special display... So you are thinking again, but so are they. Everyone sees the world from their own perspective. Perhaps people think the perspective of a physics teacher is a bit strange. We must stand up for ourselves and fight back. It is time to tell the world what good people we are to know - far more interesting than road engineers or school principals. After all, look at what they think about when they watch The Wizard of Oz!

If this positive image projection fails to recruit more physics teachers I can propose an alternative. There are about as many giant pandas in the world as physics teachers in the UK. There is a breeding programme for pandas. Now there's an idea ... .

What good people we are to know - far more interesting than road engineers or school principals. After all, look at what they think about when they watch The Wizard of Oz!

Philip BrittonHead of Physics, Leeds Grammar School, UK