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Archive October 2012

Look out for the eclipse, 14 November Marcus Wilson Oct 30

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There’s a great event coming to our neck of the woods soon (by neck-of-the-woods I mean Australasia and South Pacific) – a total solar eclipse, on 14 November (for those like NZ on the west of the international date line) or 13 November (for those on the eastern side – which won’t be many – save the odd ship). The NASA website above gives details in Universal Time (Greenwich Mean Time) and so reports it as 13 November – don’t get confused.

For those lucky enough to be in Cairns, there’s the full spectacle of a total eclipse. For us lesser mortals in NZ, it’s a pretty sizable partial eclipse, especially for those in the north of the North Island. Hamilton gets about 85% coverage at the maximum. (Note that anywhere in NZ will do – even Scott Base in Antarctica, I think, gets a few percent coverage, if you count that as NZ)

For Hamilton, the eclipse starts at about 9:20am, reaches its maximum at 10:30am, then is all done and dusted by 11:45am. Times for the rest of NZ are similar.

I thought hard about travelling over to Cairns for the event. The reason is simple – a large partial eclipse is nothing compared to the experience of a total eclipse. I was fortunate to be able to see the 1999 eclipse in Europe, from a small village in northern Bulgaria,  and, having experienced that, partial eclipses don’t have much interest. But, travel doesn’t come cheaply, and there’s a baby at home, so this time  I’m staying put. While it would be great to see another, I’m happy with one in a lifetime.

So what does a total eclipse give you that a partial one doesn’t. Here’s a list, that’s not at all exhaustive.

1. You get to look at the sun with your naked eye, quite safely.  DON’T do this at any other time.

2. The wispy corona comes into view.

3. If you’re lucky, so does the pink chromosphere (this was particularly prominent in the 1999 eclipse).

4. You get to experience the birds coming down to roost, and then taking off again.

5. If you’re lucky, ‘Baily’s Beads’.

6. Shadow Bands

7. Stars out during the day. Possibly a good view of Mercury, which is hard, though not impossible, to observe well otherwise, because it is so close to the sun.

8. The diamond-ring, as the bright photosphere bursts back into view.

And so forth. One of the things I remember from Bulgaria is just how quickly things went black in the final few seconds before totality. It was like standing in a well lit room and someone turning off a dimmer switch.

So, what do we get for 85% then? Well, not much, actually. You might not even notice that things have gone dim. The human eye is really good at adjusting to different light levels, and it’s really only when only a few percent of the sun remains that you’ll notice any obvious change in illumination. It’s fun to observe the crescent shape of the sun – but do so SAFELY – with decent eclipse glasses or solar projection. A fun thing to do is pinhole projection – put a tiny pinhole in a piece of card and project the sun’s image onto the ground or a sheet of paper.  In Bulgaria we had pinholes provided by way of the old tin roof on the cafe which our group occupied for the event – it was loaded with little tiny holes (not much good in the rain then) which gave some wonderful projections of the sun onto the tables below.

 So, when’s the next total eclipse to hit NZ? There are actually a few coming ‘soon’ – ‘soon’ being used in an astronomical sense. 22 July 2028 sees most of Otago including Dunedin eclipsed totally. But it won’t be an easy eclipse to view, coming near sunset with the sun just 8 degrees above the horizon. The same eclipse, however, tracks right over Sydney (once again the Aussies get it – though there is far more of Australia for an eclipse to hit) so one might be better off heading westward.

But then, like buses, there’s a positive flurry of them. 10 March 2035 sees NZ get an annular eclipse (the moon doesn’t quite cover the whole sun – not as impressive but pretty spooky) – then 13 July 2037 and a total eclipse tracks over the central North Island, including Napier (Hamilton lies just to the north) and then 26 December 2038 we get another chance – this one over Golden Bay, Manawatu (including Palmerston North) and Wairarapa. (Wellington is just off to the south). That will add interest to the Boxing Day barbie on the beach. The really freaky thing is that there is a small slice of land near Waipukurau that will get a total eclipse in both 2037 and 2038.

 

 

Need more grunt Marcus Wilson Oct 26

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When I came to New Zealand nearly nine years ago (it doesn’t seem that long – a sure sign of aging) I had to learn some new words. Or rather, new meanings for existing words. Things like ‘jug’, ‘dairy (as in the shop down the street), ‘five-eighth’ , ‘bush’, all have different meanings to what I’m used to. One such word is ‘grunt’. To me, ‘grunt’ is what pigs do. To my students, it’s what engines have.

Yesterday, we had a very entertaining series of talks by the third year engineering students describing a design project they’d done this year. They were set a task of building a machine that would collect squash balls from a holder and deposit them into a container a couple of metres away, as fast as possible. After the talks, there was the competition – which was great fun to watch – won by ‘The Tortoise’. As it’s name suggest, it wasn’t the quickest machine on the planet, but it had the advantage over the others of working reliably.  Sometimes (in fact most of the time in engineering) getting the job done correctly beats getting it done quickly.

Now, in the talks, a couple of the groups made a comment that the electric motors that they were supplied with didn’t have much ‘grunt’. (That, I think, was deliberate – the students had to design ways around this)  Now, grunt is not a physics word. You won’t find it in a physics dictionary. So what did the students actually mean?

 There are a few terms that can be used to describe motors. One obvious property is torque. This is the rotational analog of force – it describes the ability to impart an angular acceleration on an object. In other words, the greater the torque, the more quickly the motor can spin something up.  But ‘grunt’ doesn’t equate with ‘torque’, I think. If you have a motor with low torque, you can easily cure it with gears. Use a low gear, and you can apply more torque to a system. You know this from trying to cycle up a hill – drop down a couple of gears and it’s easier to move forward. However, this comes at a cost – it might be easier to go forward in a lower gear, but you will be doing so more slowly.

So, then, also important is rotational speed. Fast motors can spin things more quickly than slow ones. But, again, one can change the rotational speed by using gearing. If you want to turn a crank more quickly, go for a higher gear.

What I think students meant by grunt, is the combination of these two. Multiply torque by rotation rate, and you get a measure of the power. That’s the rate of supply of energy to a system. For an electric motor, torque decreases with rotation rate (the motor supplies greatest torque when it’s spinning no-where) – so it’s not immediately obvious how the product of the two will behave. Where is it maximum (i.e. at what rotation speed does an electric motor have most ‘grunt’?) In practice, with an electric motor, there’s a wide range of rotational speeds at which the motor can provide a decent power output. That means that electric motors often don’t require a gearbox, whereas with a petrol driven motor, which has a fairly limited range of rotational speeds where they can provide appreciable torque, a gear box (that is, a selection of different gears)  is essential for many applications. Another major difference between petrol and electric motors is that petrol engines don’t deliver any torque at all at low rpm (they stall), whereas an electric motor gives its maximum torque there. Hence the hybrid engine – use the electric motor at low speeds where the petrol engine is, basically, appalling; but switch to petrol at high speeds.

So, in my mind, grunt means power. At least, it does in New Zealand.

 

 

 

 

 

 

 

L’Aquila: Why you should be interested in public understanding of science Marcus Wilson Oct 24

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Yesterday I was at a very interesting discussion on ‘Open Access Publishing’. This could be a blog post in itself, but I’ll keep this brief 1. Because Fabiana would be far better to do it, and 2. Because it’s really just a lead-in to what I want to say about the l’Aquila earthquake and the ridiculous conviction of seven people (mostly scientists, including two physicists)  for manslaughter over these events.

The historical scientific journal system goes like this:

1. Author(s) writes an article and submits it to a journal. They get paid nothing for doing this.

2. Article gets sent on by an editor (who is usually paid nothing) to referees. Referees are paid nothing.

3. After to-ing and fro-ing between author, editor and referees, the article is (hopefully, from the author’s point of view) accepted for publication.

4. Journal production staff (who are paid) turn it into a pretty-looking article and stick it on a website and charge vast quantities of money to libraries or individuals for access.

In short, the journals rake in the money at everyone else’s expense. MOREOVER, the general public – that is, the taxpayers, who fund a large chunk of the scientific research that is done, can’t afford to see it.

The open access system, however, goes against this. Here, the author pays the cost of production, and the article is free for everyone.

There was a dissenting voice in the audience though. His argument ran something like this. I like the current system. It serves me well. As an author, I can get my work published for free. I don’t care that it isn’t available to the public, because the public don’t understand it – it’s targeted at other people in my discipline who can get access through university libraries.

Right, Dr Smith [not his real name], this is why you should care about public access and public understanding of science. Because it is a scientifically inept jury that has just convicted seven individuals of the manslaughter of 300 people over their role in the 2009 l’Aquila earthquake. It is a scientifically inept prosecution service that chose to pursue charges against these individuals. Governments throughout the world are not generally well populated with scientists and, moreover, they are elected by people who are not generally well educated in science. If we want to prevent the Italian insanity becoming more widespread (Fellow sci-blogger Michael Edmonds has already given another example from Russia), we need to make sure we address public understanding of science, and, part of this is public access to science and scientists.

Specifically on the l’Aquila case: the prosecution took the line that, while the seismologists didn’t CAUSE the earthquake (I’m glad they got that bit right) they were over-reassuring in their statement of risk – along the lines of that a major earthquake was unlikely but not impossible.   But what can someone employed to talk about risk do? Based on the evidence they had, that was the conclusion they reached. What were they meant to say? Advise that the whole of Italy be evacuated permanently because of its earthquake risk? (And we might as well advise the end of civilization in Japan, NZ, California, Chile etc and tell all residents to find new homes elsewhere in the world). If they’d advised an evacuation, and then no large earthquake came, one would reckon that they’d now be being sued for loss of earnings to the local economy. It is ludicrous.

The inevitable outcome of this prosecution is now unfolding. Luciano Maiani, the head of the Serious Risks Commission in Italy (and former director of CERN) has resigned, saying it is impossible to work under such circumstances. The vice-president and emeritus president have also resigned. The quote from Prof Maiani (which I’ve taken from the BBC report on this) says that the situation is

 "… incompatible with running the commission’s work in a calm and efficient manner and with its role of giving high level advice to the organs of the state,"

Quite. What this prosecution does is remove the willingness of scientists to advise governments – or anyone else -  on science. And that will set the world back decades.  Prof Gluckman (the NZ government’s chief science adviser), are you listening? This needs an overwhelming response from the New Zealand science community.

 

 

 

 

Experimental physics is easy on paper Marcus Wilson Oct 18

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Currently, down in the depths of C-building, there’s a master’s student trying to carry out the Stern-Gerlach experiment. (and also here). This is one of the classic experiments in quantum mechanics – specifically demonstrating the quantisation of angular momentum.

If you look at the text books, it’s simple enough. Pass a beam of atoms through an inhomogeneous magnetic field (i.e. one that is stronger in one region of space than another) and, hey-presto, the beam gets split into two (or more) beams, depending on the magnetic moment of the atoms. The non-uniformity of the field is essential. If the atom has a magnetic moment that lines up with the field, then it will have a negative potential energy due to the field and will move towards the region of strong field, where its energy is most negative. Conversely, if it has a magnetic moment that is against the field, it will have a positive potential energy and will move towards the region of weak field, where its energy is least positive. So the beam splits. The key result, though, is that the beam doesn’t split into a continuum, which would mean any magnetic moment were possible, it splits into discrete beams, showing that only certain values of magnetic moment are allowed. This is what quantization means – things are split into discrete amounts. What the experiment is doing, is measuring the magnetic moment in a particular direction.

Stern and Gerlach did this experiment in 1922. Having seen our poor student struggle with the apparatus, they must have put in some considerable effort, that’s now been glossed over in most books. There are all kinds of issues that need attending to. Preparing a beam of atoms (in our case sodium – we’d like to use potassium but that’s a little bit too exciting from a safety point of view) is tricky. The sample needs to be heated so that atoms are evaporated. We need a high vacuum, meaning that atoms do not collide with air molecules on their way down the apparatus. We need to make sure that we are detecting our sodium atoms not contaminant atoms that are coming from elsewhere.  And, most frustratingly this afternoon for student, we need to find where the beam is going an align it so that it falls on the detector.

The stereotypical drawing of the apparatus we see in the quantum textbooks overlooks most of what actually has to go on to get this to work. It’s slow going, tedious, and frustrating, but hopefully the student will nail it in the end. This is all too reminiscent of the reasons why I became a theoretical physicist rather than an experimental one, and the old adage…"Biology experiments wriggle, Chemistry experiments smell, and Physics experiments don’t work"

 

 

 

Why you shouldn’t cite Wikipedia Marcus Wilson Oct 16

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I, like many other teachers, am fighting a losing battle with students over use of Wikipedia.

Here’s a fun but deeply embarrassing example for the Asian Football Confederation that Wikipedia is not a reliable source of information. It shouldn’t be your first port of call for information.

 

Goodbye to the kittycat Marcus Wilson Oct 16

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We had to say goodbye to Mizuna our cat at the vet’s last night. Despite the medication, change of diet and other ‘lifestyle’ changes, he had another urinary blockage yesterday. One can’t know, of course, if that would have been his last, but FLUTD can be a chronic and expensive condition and we didn’t want to have him and our bank account suffer every month.

So, goodbye kitty cat. You were much loved and great blog-fodder.

mizuna_sept12.jpg

Considering a new car? Marcus Wilson Oct 12

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I was directed to this article by a blog on the BBC website.

It considers a full analysis of the through-life environmental cost of electric vehicles, compared to petrol and diesel vehicles. By full, it includes things like greenhouse gas emissions from the manufacture process, depletion of the world’s mineral resources, and eco-toxicity, as well as of course the greenhouse gas emissions when the vehicle is in use. The key thing about this study is that it looks at the whole life of the car, from manufacture to disposal, and considers ‘the environment’ to be beyond greenhouse gas emissions.

Include all this into the mix, and the supposedly ‘clean’ electric vehicles don’t look so rosy. For example, to produce such a vehicle requires twice the greenhouse gas emissions as to produce a conventional vehicle. And they include some real chemical nasties in their electrical components – a battery isn’t a pleasant thing to deal with. Whether electric is better than conventional then depends on 1. Your definition of ‘better’, 2. How long you run your car for before it ends up as spare parts/scrap, 3. How your electricity is generated.

The authors have estimated that if an electrical vehicle is used in Europe in much the same way that a conventional vehicle is, that there is significant benefit in terms of reduced global warming potential, by 20 – 30% or so. However, if cars are ditched too early, this dwindles to less than 10%. A major issue here is how long the batteries last for. Anyone with a hybrid car will know that it ain’t cheap to get a new battery – and batteries that aren’t up to scratch could mean that the car is scrapped long before it should be.

Moreover, there is the issue of where the electricity comes from. The authors assume the mix of generation methods that is currently in use in Europe.  However, if the electricity is predominantly generated by fossil fuel burning we aren’t going to get much benefit. One has to ask, if electric vehicles take off in a big way, where the extra power generation is going to come from. I have a nagging fear it is more likely to be coal than renewable. Coal power stations are easy to build, and there’s a lot of coal in the world still.   For example, putting this in a New Zealand context, could NZ up its power generation capability massively (and it would need to be a massive increase if everyone switched to an electric vehicle) while still maintaining the same mix of fossil and renewable sources?  I have a suspicion not, at least, not quickly.

Therefore, one might wish to consider things carefully before rushing out to buy that electric car you’ve always dreamed of. Implemented in the right way, they could be significantly better, but, get it wrong, and you may as well not bother.

 

Hawkins, T.R., Singh, B., Majeau-Bettez, G. and Stroeman, A. H. (2012),  Comparative Environmental Life Cycle Assessment of Conventional and Electric Vehicles. Journal of Industrial Ecolocy. doi: 10.1111/j.1530-9290.2012.00532.x

 

Physics is different for girls… Marcus Wilson Oct 04

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The Institute of Physics (in the UK) has just released this report looking at the uptake of the physics A-level  (done in the final two years at secondary school) by girls.  The report, titled ‘It’s different for girls‘ makes for some very interesting and perhaps dismal reading.  While it’s a UK report, not a NZ, I have little reason to think that the results would be vastly different in NZ. Moreover, given that the NZ Institute of Physics isn’t knee-deep in used hundred dollar notes (being the Waikato NZIP contact person I have some idea) I don’t think NZIP will be replicating the study here, so this one will have to do.

Here are the key findings, lifted more or less straight out of the report:

1. Uptake of physics A-level by girls is really low.  Nearly half of all schools had no girls doing physics A-level.

2. There is a huge difference in uptake of physics A-level amongst girls at a girls’ school, as opposed to girls at a co-ed school. A girl in the former group is two-and-a-half times more likely to study physics at A-level compared to a girl in the latter group. Interestingly, this difference is not seen in chemistry and biology.

3. Girls coming from a school which has a sixth-form (i.e. one that offers the final two years) had twice the likelihood of choosing physics compared to girls who had to move to a sixth-form college for their final two years of study.

So, as the title of the report says, physics is somehow different for girls. How? Why? What can be done? These are big questions. There is a strong suggestion that there is a lot of stereotyping going on – the impression given that physics is not for girls. This is particularly true at a co-ed school. That might not be deliberate on the part of the teachers (and the implication from the report is that it’s not just the physics teachers to blame for this), but the overall message the girls get is that physics is not a place where girls live.

The report suggests that parents should use the percentage of girls taking physics at the school as an indication of how well the school teaches physics. I’d be interested into delving deeper into this one. Is it true that better physics teaching means a higher percentage of girls will be involved? Interestingly, in my physics degree at Cambridge, there were approximately 100 male students in the third year, and exactly one female student. Does this mean that the teaching I got at Cambridge was really bad?

How do we counter this?  A lot of examples of physics-in-action are inherently boy-focused. Cars, for whatever reason, do seem to be more boy-ish than girl-ish, and cars do make nice, easy examples to use in much of physics. We, the teachers, may need to be a little less lazy in our selection of contexts in which we present the physics.

How am I shaping up? After all, this blog is intended to show physics in action – that is, physics is something for everyone. Including girls. So, a quick flick through the past few entries reveals that I’ve talked about:  Galaxies, hobbits, cats, the Higgs Boson, Auckland, our most utterly adorable baby, static electricity, time travel in a car (tut, tut on this one), neutrinos, building with reinforced concrete, who owns water? (Oops, I mean, who has rights to water?), Brownian motion, testing students …

I don’t think that’s desperately male-centric, but you judge for yourself.

 

Distant galaxies and hobbits Marcus Wilson Oct 01

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I haven’t read ALL of Tolkien’s work, but I suspect space-travelling hobbits don’t feature anywhere. However, what do feature are hole-dwelling hobbits, and I had the fun of seeing their holes in the countryside near Matamata yesterday. The original set for Lord of the Rings was mostly removed after filming, and rebuilt for the filming of the Hobbit trilogy.  (Trilogy? Since when was The Hobbit a trilogy? This is just milking money out of Tolkien fans, isn’t it?) But this time the set will remain, for all to see, for an appropriate fee of course. It certainly was fun to have a look around – what made it was the commentary provided by our excellent guide.

One of the fascinating things pointed out was the perspective tricks that were used. For The Hobbit, there are three different versions of some of the holes.  One, a ‘large’ version, appropriate for a normal-sized actor, dressed as a hobbit, to walk through. One, a smaller version, to make the dwarfs look bigger than the hobbits. And another, an even smaller version, to make Gandalf look bigger than the dwarfs. And the three had to be identical.

And then there are the perspective tricks. To make the view look like it is over a longer distance, the more distant holes are of smaller size than the nearer ones. On a 2d movie it works – your mind interprets what you see as being of equal-sized holes spread over a larger distance. But being there in 3d you see it more as it is.  

That’s the problem that’s faced when determining the distance to distant stars and galaxies. Just how far are they away?  The moon, and anything further away, we perceive as 2 dimensional. We can’t get any 3-dimensional cues and so we have no idea, just by looking, of how far away they are.  So how can we measure distance to the stars? 

One way, which works for the nearest stars, is parallax. The earth orbits the sun, and six months from now it will be about 300 million km away from where it is now. That gives a different viewpoint. The nearest stars, therefore, appear to move against the background of stars that are further away. We can therefore use a bit of simple trigonometry to work out the distance to the star. Indeed, one of the units of distance in astronomy is the parsec – one parsec being the distance over which the diameter of the earth’s orbit subtends a parallax angle of one arc-second.  Essentially, using parallax in this manner is like viewing the situation with two eyes – 300 million km apart.

Parallax, however, only works for our nearest stars, since the distances to our neighbours are so huge. To work out distances further away, there are other methods – such as looking at the intensity of Cephid Variable stars, and, for really long distances, the famous redshift. However, somewhat disappointingly, neither of these are exemplified by the Hobbiton movie set.

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