SciBlogs

Archive February 2010

Ethicis in physics Marcus Wilson Feb 26

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Physicists don’t usually have to put too many proposals before ethics committees in their working lives. (For the uninitiated, in simplistic terms an ethics committee is where a proposal for an experiment on/involving animals and/or humans will be discussed, to see if it is ‘appropriate’. Universities are full of them, and my biologist / psychologist colleagues know them well.) Compared with other forms of science, physics probably has rather few ethical dilemmas.   But I’ve had one this week.   I’ll be deliberately vague, but hopefuly you should get the picture.

I’ve been asked by a reputable  journal to review an article (let’s call it ‘A’) as part of the standard peer review process.  What are my thoughts on its content and quality, etc.?   Now, I have a look at the article in question and I find that the authors refer heavily to another article (let’s call it ‘B’), in a journal that I haven’t heard of.   Thanks to the magic of the internet, I quickly retrieve ‘B’, and have a look at it.  No problems so far, but I’m now interested in finding out a bit more about the mysterious journal in which it is published.

The mighty Google works a treat – not only do I find the journal’s website, but, more interesting, up comes a lot of links to blogs where this journal’s name is used in the same sentence as ‘quack’ and ‘pseudoscience’.

Now, here’s the problem. My job is to review article ‘A’, not article ‘B’.  My review of ‘A’ should be on the merits of article ‘A’ alone. Shouldn’t it? The fact that the journal where ‘B’ appears has been discussed in a fairly savage light on many science blogs should not influence my thinking as to whether ‘A’ is a piece of quality science. (?)  After all, blogs are not necessarily reliable (Says he who is writing a blog) – but they are in a sense ‘peer reviewed’ – that’s what the comments do.

 So, what should I do?  Decline to review the article? But that just passes the problem to someone else. Try to get one bit of my brain to ignore what another bit knows? Tricky one this.

I suppose one thing it shows is how difficult it is for anyone to make a truly independent judgement about anything.  Any background knowledge starts to influence the way you see something. 

Appraisal doesn’t equal Evaluation Marcus Wilson Feb 25

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I spent yesterday afternoon in a seminar discussing how my teaching can be analyzed for its effectiveness. One much used word is ‘appraisal’.   Students may recognize that as meaning those annoying questionnaires that get thrown in front of them in the last two minutes of the final lecture of the year, in which they need to answer questions on the content of the paper and the performance of the lecturer. There’s a vague implication that the university wants to know from its students how they feel about the teaching they have received, but it’s not often made clear.

It was very interesting to learn yesterday exactly how different lecturers use the appraisals.  Students might be in for a shock here. It depends very much on the lecturer.  Some lecturers carefully go through every form, pull out the major themes from student comments, think how they can improve and make changes for next year’s teaching.  Then, next year, they pick their appraisal questionnaire questions carefully so they can assess whether their changes have been effective.

But some lecturers do nothing with them (other than maybe check their overall score isn’t too bad.)   All that time the poor student has spent identifying three ways in which the lecturer could improve, etc - the lecturer may choose not even to read it, let alone do anything about it.

Also, something that struck me this morning, is that the appraisal questionnaires that we gave our students here at Waikato in 2009 are not very much different from those I had to fill out as a student in Cambridge in 1989.   Twenty years have passed since I first sat in lectures and, on the face of it, not much has actually changed in terms of how the quality of teaching is reviewed (or not).  I now wonder what happened to the forms I did back then - did anyone take notice?  

But there is actually, as I’m learning, a huge amount of research on how to evaluate your own teaching effectively.  So why do we seem to focus so much on those questionnaires? 

What’s so dangerous about high voltage? Marcus Wilson Feb 24

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There was a short piece on the television news last night about the ‘Taser’ weapon now being used by the NZ police force.  I always listen carefully to popular media when they discuss electrical things, since there is a quagmire of terminology that is often used incorrectly.   This time, however, I didn’t pick-up incorrectly used terms – "50 thousand volts" was mentioned, but fortunately not in the context of 50 thousand volts of current, or 50 thousand volts flowing through it, or a power of 50 thousand volts.  Well done TVNZ.

One gripe though, the fact that it is 50 000 volts is only half of the issue. A Van der Graaf generator, as loved by all teachers of physics, (especially those with long hair) will happily get to hundreds of thousands of volts and pose no threat to anyone, other than the odd ‘zap’ that you wish to inflict on your students.  The point is that the current delivered by a Van der Graaf generator is tiny. Contrast that with the mains supply. It’s only 230 volts, but is designed to deliver large quantities of current.  That’s fine if the device on the end is your electric kettle or heat pump, but if it’s you then you could be in trouble – much more so than getting a controlled shock from a taser.  (Not that I would volunteer to experience the latter.)

Centrifugal carrot Marcus Wilson Feb 23

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We bought a vegetable juicer recently.   At one end you feed in all those delicious carrots and corguettes that have been growing nicely in the vegetable patch, and at the other end comes out carrot and corguette juice.  Get the right combination of vegetables, and it’s a nice drink. (I don’t recommend kohlrabi though. Actually, we haven’t found anything nice to do with our kohlrabi other than adding it straight to the compost bin – the trouble is we planted rather a lot of it – if anyone has any tips they would be greatly appreciated)

 Our juicer is a ‘centrifugal’ type.  That means the veggies get ripped apart first of all by a rotating blade with little piranha-teeth on it, then the bits get thrown against a mesh where the centrifugal force squashes the juice out of the veggie-piece. The juice flows through the mesh and then is collected, whereas the bits make their way to the top of the revolving bit (which is wider at the top than the bottom) and are then thrown out and collected elsewhere.   Very efficient, and very viscious.   The warning about not inserting your fingers into the machine is there for good reason.

I’m not sure just how fast the centrifuge bit rotates, but it is certainly beyond the ability for the eye to ‘see’ the movement – everything just blurs into one. So I would say it is at least 20 times a second, possibly a lot more.   It has a radius of about 5 cm or so.   A little bit of physics calculation tells me the centripetal acceleration of a lump of carrot at the centrifuge rim – namely 4 times pi squared times rotation rate squared times radius.  (The acceleration is equal to the angular rotation rate squared times the radius.)   So we’d have 4 times 3.14 squared times (20 per second) squared times 0.05 metres which comes to about 800 metres per second squared. 

Compare this with the acceleration due to gravity  of about 10 metres per second squared.   The veggie-lump experiences about 80 times this. I suspect this is a conservative estimate.  So it gets squashed very nicely.

N.B.  No apologies made for referring to ‘centrifugal’.  See  http://sci.waikato.ac.nz/physicsstop/2008/12/going-around-in-circles.shtml and the xkcd cartoon below.

Centrifugal Force

The wrong kind of question Marcus Wilson Feb 19

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Following on from yesterday’s discussion of the paper by Gire et al. I’ll remark on one little aspect of this study that physics teachers and lecturers need to take note of. (Well, in my opinion they do, and I’ve got a steadily increasing pile of literature to back me up on this).

One of the questions that was asked of the students was "When I solve a physics problem, I locate an equation that uses the variables given in the problem and plug in the values".  Now, I would say that is not a good approach. No no NO NO NO! That approach yields no understanding to the student about what is going on.  But in the sample group, about 70% of first year physics majors, 80% of second year physics majors, and 90% of first year engineering students agreed with that statement.  The authors describe this worrying result nicely:

The unfavourable responses of year 1 and 2 students are striking because it suggests that students in the first two years of undergraduate study find the plug-and-chug stategy to be productive in solving physics problems

What this tells me is that we (that is, the teachers) are setting the wrong kind of problem, even in second year physics.  (By year 4 only 40% of the students agreed, and there is some comfort to be had that 0% of graduate students thought this approach was the one to take. The message that physics is not about sticking numbers into formulae gets across in the end, but it takes a long time)

When I set assignment and exam problems, I try to do so in a way that assesses the students’ knowledge of the underlying concepts, not their ability to choose and manipulate an equation.  But setting this kind of plug-it-in problem is pretty ingrained – for example it permeates many university physics textbooks, and it is hard to prise myself out of that mode of operation. If we ask questions that lend themselves to the ‘plug-and-chug’ or ‘stuffing numbers into formulae’ approach, we only have ourselves to blame when our students hit third year without understanding  the physics concepts that we thought we taught them.

Incidentally, the NZQA scholarship physics exam is a great example of setting questions that probe a student’s understanding of physics, rather than their ability to pick equations of a rack. If you are thinking about doing this exam – and agree with the statement "When I solve a physics problem, I locate an equation that uses the variables given in the problem and plug in the values" you will be in for a very big shock. 

 

How does a physicist think? Marcus Wilson Feb 18

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As part of my reading for the Postgraduate Certificate in Tertiary Teaching (henceforth known as the PGCert(TT) )  I’ve come across this article by Gire et al. on how physics students think.   The study looked at how closely the physics-thought-processes of undergraduate and graduate students aligned with the physics-thought-processes of practising physicists.    In other words, do students studying physics think like physicists?

To do this the authors studied students taking physics at university (be they physics majors or doing physics as part of another programme, e.g. engineering students),  and asked them a set of agree/disagree questions that exposed how they thought. For example: "When I solve a physics problem, I locate an equation that uses the variables given in the problem and plug in the values"; "In physics, it is important to make sense out of formulas before I can use them correctly"; and ‘There are times I solve a physics problem more than one way to help my understanding".   I would answer these questions: disagree; agree; agree; in that order.

Now, there are a couple of interesting findings from this work. First of all, students who enter first year wanting to major in physics enter the classroom substantially more expert in their thinking than those wanting to study engineering. Perhaps that’s not surprising – those who think like a physicist want to study physics. Secondly, students maintain this level of expertise through 2nd and 3rd year (show no improvement or loss), but improvements are significant once students reach 4th year (in this study the physics degree in question was done over four years) and there are further improvements for graduate students. 

 This prompts some questions – are the first three years in this degree doing very much for the students, and are there problems with the way physics is taught to engineering students?  These have significance for the way I teach – my second-year solid state physics class after Easter will mostly contain engineering students, not physicists, but they are being taught by a physicist (me). Should I change the way I teach to account for this? And how?

Gire, E., Jones, B. and Price, E. (2009) Characterizing the epistemological development of physics majors. Physical Review Special Topics – Physics Education Research 5, 010103. 

I hate maths… Marcus Wilson Feb 16

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I’ve spent most of the morning grappling with a bit of troublesome mathematics.  I can tell that I’ve had enough, because I’m starting to see greek letters tango with roman ones across the computer screen before raising themselves to inappropriate powers and differentiate themselves into oblivion, and graphs of noisy data that are beginning to look suspiciously like Mt Pirongia…I think a change of topic is called for for the afternoon.

pirongia_change.jpgFortunately, there is our first Cafe Scientifique of the year tonight, in which my university colleague Adrian Pittari will be talking about pyroclastic flows from some of the world’s more exciting volcanic eruptions (well, exciting if you viewed them from an appropriate distance). Should keep my mind off the maths for a while.

 (P.S. The pink line is not REAL data – I made it up to give me something relatively mindless to do over lunchtime)

Technology wins again… Marcus Wilson Feb 15

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It was nice to hear this morning that someone actually has won the America’s cup, and there is now the prospect of getting back to some proper racing again instead of slugging it out in a courtroom. In the end it was superior technology, rather than a superior legal team, that won the day for Oracle. (Though the two may not be entirely unconnected.) Oracle simply had the fastest boat – and no amount of skill by Alinghi could overcome that advantage.

It’s another example of how sport is more and more dominated by science and technology. Gone are the days where the winning was down to superior strength or skill, now it is down to having the best equipment, whether it is the rugby jersey that an opponent can’t grab hold of, a slippery swimsuit, or a correctly tensioned tennis racket.  OK – I exaggerate – you can’t expect me to beat Roger Federer simply by giving me a good racket to play with – but give Federer a 1950′s racket and I bet most of the other top players would knock him off his pedestal relatively easily.  (There’s an intruiging thought – someone could sabotage his rackets – might be the only chance anyone has of beating him in the near future….)

Of course, the best equipment costs money (especially in sailing, where the cost of the boat can on occasion exceed the cost of your lawyers) which is just one of the reasons why sport is such big business.

Sometimes sports rules have to change (or be interpreted on the hoof) to cope with changing technology. (Anyone remember Dennis Lillee’s aluminium cricket bat?) It’s not just for the players – the introduction of video replays in sports like rugby and cricket was invetiable given the mockery they made of some umpiring decisions – and the use of Hawkeye in tennis is a step forward in my opinion.

I await with interest to see what as-yet-undeveloped technology will be commonplace in next twenty or thirty years’ time.

Does my teaching work? Marcus Wilson Feb 11

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This year, I’ve finally decided (more accurately, finally got around to doing it) to undertake a Postgraduate Certificate in Tertiary Teaching.  In plain English, that means do some training that actually prepares me to teach at university. "What?" I hear you say – "You mean you haven’t got any qualification to teach at university?".  Nope. And the same is true of most lecturers, in most universities. They are appointed because they are good at their research, and it is just assumed that if you stick them in front of a class of students the students will somehow come out better off. And, as every student or ex-student (i.e. me) knows, sometimes it happens, and sometimes it doesn’t.

Anyway, as part of the PGCert (Tertiary Teaching), I’m thinking about ways that I can know whether or not (probably the latter) my students have understood what I have been teaching. A brief look at the literature shows that there are numerous ways of doing this in the context of physics.  Very crudely, you can test your class before you teach something, and test them again afterwards.  The improvement equals their learning.

Or does it?  First of all, learning, if not exercised, diminishes over time.   Test them a week after you taught it, and their performance may be good. Give them a similar test at the end of the semester, or in the next semester, or in two years’ time, and the scores will be lower. However, the learning doesn’t usually decay to zero – usually something sticks for good.

But the thing that grabbed me on reading this recent paper by Sayre and Heckler is the effect of ‘interference’ by a similar, but different topic.  After learning about the topic of interest (in this case electric fields) the students do well in a short test.  But a couple of weeks later, they do poorly, not because of the passing of time, but because, at that time, they are being taught another topic that they are confusing with the first (in this case electric potential). Tested again later on, when the confusing interfering topic has been taken away, their performance has risen again.

So it’s not all that easy to assess whether learning has taken place.  With this example, have the students REALLY learned about electric fields properly? One could perhaps argue that, if the learning had been deep enough, their understanding would not have been confused by a related, but different, topic.   One could perhaps test them yet again, on both electric fields and electric potential, at a still later date, and see if the confusion has remained.  What I thought would be a very simple procedure suddenly gets rather complicated.

Sayre, E. C. and Heckler, A. F. (2009) Peaks and decays of student knowledge in an introductory E&M [electricity and magnetism] course, is the effect of ‘interference’. Physical Review Special Topics – Education Research, 5, 013101  

Dynamic equilibrium Marcus Wilson Feb 10

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I keep a list in a notebook about possible things I could write a blog entry about. When I see something in the media, or something happens at work, anything to prompt me to think about a particular area of physics really, and I scribble it down and may choose to inflict it upon the world at a later date. For example, I thought I got a good one a couple of weeks ago when I learned about an impending mass-overdose on homeopathic medicine as a protest against it being stocked by chemists in the UK.  Then I discovered it had been extensively covered on about six thousand science blogs already.  I didn’t add to that list. (In case you are interested, and have somehow escaped reading about it, have a look at the campaign website on http://www.1023.org.uk/ )

On my list is ‘dynamic equilibrium’.   I put in on there after writing my blog entry about feeling ‘cold’ radiating off something – it’s a very much related topic, and an important one in physics and chemistry (and I think probably biology too), but I haven’t got around to talking about it.  I’ll give you a physics-coloured example.

We say things are in equilibrium when thing appear to stay the same. For example, the telephone in my office is in thermal equilibrium with the air in my office. That is, the temperature of the phone is the same as the temperature of the air (roughly speaking). But that’s not to say that nothing is happening.  Two objects will always exchange heat with each other - if they touch then through conduction, if there is a fluid involved then through convection, and if there is a line-of-sight between them through radiation.  So the air is transferring heat to the telephone. Likewise, the telephone is transferring heat back to the air. But the rates of transfer are equal. Consequently the telephone gains as much heat as it loses, and its temperature stays the same

Migration is another example. The population of a particular town might stay the same from one year to the next, but the people in it do not.  People are born, people die, people move away, and people arrive, but the number being born and immigrating equals the number  dying or emigrating. Overall, the town may not show any changes at all (the ‘equilibrium’ bit), but the components that make it up (the people) are constantly changing (the ‘dynamic’ bit).

Really, the important thing for physics is although macroscopically (on a large scale) things might appear to be constant, look on a small enough scale and they are not.

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