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October 2013 Archives

On Saturday morning I held a session for school students preparing to sit the 2013 Scholarship Physics exam. My intention is to help them prepare for this. It's a tough exam, aimed at rewarding the best school students in the various subjects. I talked through the principles behind answering various types of question, e.g. 'estimate' questions, mathematical questions, 'explain' questions and so forth, drawing heavily from previous exam papers. One of the questions we talked about was from the 2010 paper. Students were asked to critique the voice-over on a well-aired road safety ad of the time. (You can find the ad here - isn't YouTube wonderful?).

I won't go into the physics here, partly because I've already done it in a previous blog entry. Suffice to say that the advert will get approximately zero out of ten for scientific accuracy. However, it does get its central message across rather well, I think: Excessive speed causes crashes. So, I think it's reasonable to ask the question: "Is this a good advert?". We had a brief discussion on this on Saturday. There are several points that could be made. In defence of the ad, it does, I think, what it is designed to do - get people to think about how fast they drive.

But does it do more harm than good? It certainly doesn't promote scientific literacy by using science concepts incorrectly. We've already seen numerous examples of how lack of science understanding among the public can lead to outrageous decisions being made by politicians who rely on the public vote: governments drag their feet on tackling climate change (coz it will hit the voters in their pocket - not a smart political move) and in Hamilton we've had a narrow squeak over fluoridation - fortunately in the latter case the science won and a citizen's referendum has overturned a ridiculous decision made by the Hamilton City councillors. 

But the science can sometimes be hard to explain well. After I gave him what I thought was a clear, concise and accurate statement of what I thought the advert should say, my father-in-law replied on Saturday afternoon "no wonder they've done another explation - it's easier to understand" (or words to that effect).'s not right.

Tricky one this.




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A highlight of the recent NZ Institute of Physics conference was the Dan Walls medal talk given by Matt Visser. Matt has been working on general relativity. That's not desparately unusual for a physicist, but Matt has been successful in working on some of the crazier aspects of relativity and getting it published - wormholes, dumb holes and the like. He gave an entertaining talk - perfect for closing the conference.

I was particularly taken by the description of the analogies between light and sound. It's unsurprising that there should be analogies between the physics of light and the physics of sound in that both are waves, but the extent to which the analogy can go surprised me. For example, it is possible to get Hawking radiation with sound. 

Hawking radiation is predicted to be radiated from black holes. I say 'predicted' because experimental evidence is still scant. It allows black holes to 'evaporate' by emitting radiation from their event horizons (Within the event horizon nothing escapes the black hole - not even light. Once you've passed that boundary, you have a one-way ticket to a singularity). There's an analogy between the event horizon of the black hole and an acoustic shock-front (sonic boom) created by an object moving faster than sound. In the case of the former, once you are past the event horizon you can't get back out, and in the case of the latter, it's not possible for a perturbation that occurs behind the shock front to have an effect in front of it - in order to do so it would need to go faster than sound. 

It turns out that many of the equations governing the situations are similar, including those necessary to produce Hawking radiation. The implication is that one should be able to create Hawking radiation from shock fronts created with supersonic fluid flow. And indeed it has been done - what one might consider an effect of general relativity demonstrated in a fairly simple lab experiment. Quite beautiful. Black holes (well, OK, certain aspects of them) on your lab bench.


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The last couple of days have seen our Engineering Design Show. This is where our 2nd/3rd/4th year Engineering students get to talk about and show off the various projects they've been working on in the last year. It's very interesting to see the range of activities going on, and there are some 'competitive events' - this year the 3rd year mechanical engineering students had to design a seed-planter to automatically put pine seeds into seed trays - accurately, quickly and cheaply. 

For me, the stand out talk was by one of the fourth years - Matt Dromgool. He talked about a solution to the problem of heating in electric cars.

This problem is something that had never occured to me, though it is extremely obvious when one thinks about it. In a petrol/diesel car, providing heating to the interior is easy. Just blow in some of the waste heat from the engine. A small radiator and fan does the job and often has the added bonus of saving your engine from overheating when the main fan fails. The one obvious disadvantage of this method is that you don't get instant heat when you start the engine from cold. When it's minus ten or lower outside, instant heat is often what you want. Some cars have wire-mesh heating elements built into the windscreen for quick defrosting on cold days. 

However, an electric engine doesn't generate much waste heat. There's not enough to warm the interior of the car (and, more importantly, the windscreen) adequately. So how do manufacturers of electric cars solve this problem? The simple solution is to stick in a resistive heater - just like a bar element on an electric fire. But where does the energy come from? From the battery, of course. The trouble is, to heat the car, you need a lot of heat. Matt put up some data from one electric car manufacturer that showed the range on a full charge dropping from about 160 km to about 50 km when the heater was turned on fully. That's a pretty severe drop in performance. 

Ironically, a lot of electric cars carry air conditioning systems. That's because many are little more than petrol cars with the petrol engine pulled out and an electric one slotted in - not much else gets changed - and the air conditioner stays in place. So an obvious solution is to allow  the air conditioner to run in reverse - to move heat from outside the car to inside, not the other way around. This is what a domestic heat pump does - the same system can either heat your house or cool it depending on the direction in which the fluid flows. So Matt's project looked at converting a conventional car air conditioner (which just does the cooling bit - it has no need to supply heat in a petrol car) and modifying it to allow it to run on a reverse cycle as well, to do the heating bit. A nice, simple, cost-effective solution. Sure, it still runs on electrical energy, but it uses much less energy than stuffing a resistive heating element in the car. It also carries the advantage that one can now get instant heating when required on really cold days. 

I wonder when we'll start seeing them in electric cars. 





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....Well, what do you think? No surprises this year.  Francois Englert and Peter Higgs have been awarded this year's Nobel Prize in physics for the theoretical 'discovery' of the Higgs mechanism. The citation, however, I find very interesting:

for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted funamental particle, by the ATLAS and CMS experiments at CERN's Large Hadron Collider.

First of all, can one 'discover' something theoretically? Sure, one can predict the presence of something theoretically, but can it be discovered by a piece of theoretical analysis? I'll let you debate the semantics of 'discovery'. 

Then, note how the prize isn't given for the discovery of the Higgs Boson.  The word 'boson' doesn't get a mention at all, in fact, though it is implied by the words 'predicted fundamental particle'.  The boson is merely a piece of experimental evidence  - a rather key piece, it has to be said, given it's the only thing about the Higgs mechanism that is really observable - but still only a piece of evidence for the Higgs mechanism. It is the explanation of the origin of mass that is the notable thing here.

Well, actually, not quite. Note how the citation is for "...a mechanism that contributes to our understanding of the origin of mass..." It stops short of saying that the Higgs mechanism explains it. Is there more to come?

Then finally the experimental credit is given. The Nobel Prize isn't generally awarded to large teams of people. The ATLAS and CMS teams are vast indeed (see the list of authors on the ATLAS and CMS Higgs Boson discovery papers here and here) but these teams are rightfully given credit for their part in confirming the Higgs mechanism.

So, well done to you all. 

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One of the many good education-focused talks at the NZ Institute of Physics conference last week was by Kerry Parker of Te Aho o Te Kura Pounamu and the University of Otago. She described her own and  her students' experiences of attending the International Young Physicists' Tournament. The tournament stretches students far beyond the confines of the secondary school curriculum by using really open-ended questions (so open-ended that the 'right' answer is actually still a matter of debate and research.) Kerry showed a few film snippets of the tournament and interviews with students, both during and after it. One student quote I wrote down since it explained beautifully what physics is about:

Physics is not a set of laws inscribed in stone but rather a means to explore and understand the world around us.

I would challenge anyone to put it more succinctly than that. 

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