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September 2009 Archives

The amazing people at the Science Media Centre in Wellington have put together www.sciblogs.co.nz , all your favourite NZ science blogs in one easy to access site. Physicsstop is there, along with a host of others. The only downside is that with such a great collection of items to read, when am I going to find time to do any work?

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The speed of sound in air is about 330 metres per second (which means it takes  three seconds to go one kilometre). So count the seconds between the lightning and the thunder, divide by three, and you have approximately your range from the lightning in kilometres. (Divide by five for miles). So, the lightning that struck about 4pm yesterday, which took at most I'd say quarter of a second between sight and sound, would be 0.25 divided by 3 which comes to awfully close.

I can't say I've ever heard a bomb going off, but I reckon that sound must have been like it.

For more on my opinion of thunderstorms, click here

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So PhysicsWorld has done a nice article on some of the 'engineering' solutions that might be available for tackling global warming.

Generally they are pretty ambitious global-scale plans to turn down the thermostat a bit, given the premise that either carbon dioxide emissions will not fall sufficiently or that, even if they did, the earth would still be too hot and something else will be needed.   They fall into a few categories. First, there is the CO2-vac. Suck up that excess carbon dioxide using whatever technology you can make work. Secondly there is control of the earth's surface. This might mean things like planting crops / forests that are a little more reflective to sunlight than current crops. And thirdly, there is control of the amount of sunlight that hits earth.

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I've been reading in PhysicsWorld about some grand ideas for controlling the earth's climate by engineering on a global scale. Some sound pretty fanciful, though some might be just plausible. But before I get there (which will probably be another entry) I think it's worthwhile reminding you what the greenhouse effect actually is. As in, why is it a greenhouse gets hot, and what has this got to do with the atmosphere?

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Eco-systems are of course very complex things - the success of one species is linked to the success of another, which is linked to another, and all of which are linked to outside factors such as climate etc etc.  Now there is direct evidence of another degree of complexity in the ocean eco-system, namely that fish (and other swimmy things) have a significant role to play in mixing the ocean.

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If ever you thought reading a physics textbook was like reading a page of Tolkein, this one is for you. (Thanks due to University of Nottingham). Each symbol has a short video behind it. 

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I love the headline at the end of last week 'Wellington quake risk halves'. As if you can wake up one morning and find that the chances of an earthquake happening today are suddenly half of what they were yesterday just because someone says so.  What next - someone decreeing that summer will last 12 months of a year and so magically it does?

 

 

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Have you ever had one of those days when you have worked flat out all day and seem to have accomplished nothing?

I think that's today.  My desk looks like a tornado has been through the office. Now, I wonder, statsitically speaking, how many tornados I'd need to come through before one picked up all the loose bits of paper and kindly deposited them in the right places in the filing cabinet.   I live in hope.

I'm off to enjoy a coffee.

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I've just been putting together a presentation for final year school children on the NZ scholarship physics exam.   NZ Scholarship is awarded to the top 3% or so of students in a particular subject in a particular year, and there is some big money up for grabs.

But the exam questions for scholarship are hard.  Really.  I find them hard (remember I lecture physics at university - I should be able to do school physics stuff).   I can open an exam paper and think ...err...how on earth am I meant to do that? If that's my response to a physics question, then I can only think that it will be the response of most people sitting the exam.

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Here's a lovely quote that students will empathize with:

"A recent study on the use of vectors by introductory physics students summarized the conclusions in two words: "vector avoidance". This state of mind tends to propagate through the physics curriculum. In some 25 years of graduate physics teaching, I have noted that perhaps a third of the students seem incapable of reasoning with vectors as abstract elements of a linear space...I have come to regard this concept of a vector as a kind of conceptual virus, because it impedes development of a more general and powerful concept of a vector..."

David Hestenes, Oersted Medal Lecture 2002: Reforming the Mathematical Language of Physics. Reference made to E. Redish and G. Shama, AAPT Announcer vol 27, p98 (1997)

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Photo from NASA

Have a look at the latest pictures from the upgraded Hubble Space telescope. I particularly like this one. The universe really is a huge place. If we look carefully enough, maybe we'll even find a solution to the All Black lineout.

 

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OK, following from my ability to break web-applications (it's not the first time I've done it - a couple of years ago I managed to break one of our staff-only applications on our website - about 30 seconds later I got a call saying "we don't know what you've done but you weren't supposed to be able to do it...") you may be wondering what has the log of -1 to do with my blog, apart from both having the letters 'log' in them?

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Well, what do you know? I write an entry about complex numbers and the next thing that happens is my blog editor breaks down and I get an error message "cannot take the log of -1 at lib/MT/Template/ContextHandlers.pm line 2032". Our nice support people have fixed it now, so hopefully I am readable again.

For those of you that don't see the mathematical irony, the log of -1 is a complex number. (Logs tell you what power to raise 10 to in order to get your number; so log 1000 is 3, log 100 is 2, log 10 is 1, log 1 is zero, log 0.1 is -1 etc etc, but there is no real log of -1. Logs of negative numbers are complex.)

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Sometimes the divide between physics and mathematics is a thin one. Particularly between theoretical physics (which is what I do most of) and mathematics. The difference is that physicists have to keep one foot loosely planted in reality. It's true that sometimes it just the tip of a little toe that's behind the reality-line, but look hard enough and you'll find realism in all that a physicist does.

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Fog

Well, what does one expect living in Waikato? Four days of gorgeous spring weather in a row is a bit much to ask for.

So the fog was back this morning, and with it the idiot car drivers who don't put their lights on. Why? Do they want to die? A white car with no lights in fog is really hard to see. White is the worst colour of all; the water droplets in the air scatter the sunlight so much that the environment appears uniformly lit from all directions, and a white surface just reflects that illumination, meaning it appears at exactly the same luminance (brightness) as its environment. Grey viewed against the same tone of grey. Not easy to spot without lights. Dark cars are a little better; they appear darker than the grey environment and are so a bit easier to see.  But lights help so much. Switch them on.

 

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Recently I was asked by a scientific journal to review an article that had been sent to them. This is pretty standard procedure for journals, and every scientist will know what I am talking about. For those non-scientists, peer review is a way of ensuring (or rather, trying to ensure) quality in scientific publication. If someone writes an article and submits it to a scientific journal, the editors will send it to people reasonable competent in the field for them to comment on. For example, is the subject matter appropriate for the journal? is the method sound? are the results believable? are the conclusions backed up by the results? etc etc.

 

 

 

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We've had our dishwasher for a couple of years, acquiring it after the one we inherited with the house went out with a bang (and shot sparks the entire length of the kitchen.) It's a nice dishwasher - that is, it washes dishes nicely, but it's got an annoying habit that I have just experienced for about the zillionth time. If I've got the kitchen sink full of water, and the dishwasher reaches a stage in its cycle where it pumps its water out, it pops the plug out of the sink and I lose my water. (The old dishwasher did this occasionally - the new one does it every time.)

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OK - I think I've got it now.  Why is the sky blue? - or at least, why is it that low wavelengths are scattered more than high wavelengths?

 

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I was reading in the New Zealand Herald at the weekend about a curious problem relating to electric cars. But it's not a technological problem - it's one of language.

My car runs on petrol. It's fuel economy is pretty easy to measure. Start with a full tank, take a note of the odometer, run it until the gauge gets low, fill it with fuel, noting carefully how much goes in, take another note of the odometer, and then divide your kilometres by number of litres for kilometres per litre, or divide your litres by your kilometres and multiply by 100 to get litres per hundred kilometres. (Or work out miles per gallon if that's what you want.)

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