,,,I have the following question. Why is it that electronic engineers like to find themeselves the most labyrinthine building on campus and place their reception area somewhere that no-one is likely to find? I can only assume it is because they don't want their own private world disturbed. Best leave them be.
A light-hearted look at everyday physics going on in the world, written by a physicist but intended for a general audience.
Sundials are fun. As someone who visited a lot of stately homes as a child (usually under duress), I found sundials in the gardens a welcome distraction from the monotony of trudging round a place with no other redeeming features that adults somehow seemed to find attractive. Not all adults did, I'm sure, but certainly my parents did.
First, there's always the question of whether the sun will be out. And if it isn't out now, will it be out soon? How long do I wait for the clouds to clear? Then there is the dechiphering of the roman numerals on the dial, and the question of whether to adjust an hour for British Summer Time. Then comes the excitement of whether the sundiial is actually telling the correct time. The answer was usually 'no'. Even when a sundial is correctly calibrated for its longitude, there is also the thorny issue of the Equation of Time. It can still be out by as much as 16 minutes, depending on time of year.
Sundials at these houses usually came in two forms. There's the 'traditional' pedestal-style sundial, with a metal dial and a triangular piece of metal (the 'gnomon') sticking up by which to cast the shadow, and there's the wall-mounted sundial. Here's the wall sundial at UWA. It's marked out in terms of 'hours till sunset', making it pretty useless in terms of telling the time, but a bit more exciting than normal. It's complemented by a beautiful swan weather vane which, given the usual predictability of the winds, also doubles as a time-piece in summer.
Now, here's an interesting question about wall-mounted sundials. Besides from having to be mounted on south or north facing walls depending on hemisphere, an obvious disadvantage would appear to be that they will only be in sunlight for a maximum of 12 hours a day, even in summer. But that is not actually true. It may seem odd, but it is possible for a wall-facing sundial to have more than twelve hours of sunlight per day. That comes down to the inclination of the earth's orbit to the equator.
I remember this point being inflicted on us with delight from our lecturer in our first year at university. We had a computing project to do (in FORTRAN77 - remember that?) and the task that our sundial-fanatic of a lecturer got us to do was to plot out the markings for a wall-mounted sundial given its latitude (that way everyone got a different task so we couldn't copy each other's results). Fortunately he did provide us a nice formula for the angles of the various markings, but programming it was still a bit of a mission. I was very relieved to come out of it with a good result.
What I did learn, in addition to some FORTRAN and trigonometry, is that there is more to the sundial than meets the eye.
A couple of hours ago I gave a talk to the 'education group' in the Faculty of Engineering and Mathematical Sciences at the University of Western Australia. Broadly speaking, the audience was a group of physicists and engineers who are interested in education.
I recycled a talk that I'd given a couple of years ago on the role of mathematics in physics - specifically comparing and contrasting how practising physicists and students think about how maths works within physics.
My conclusion from the research I've done (based on interviewing students and physicists (you can read it in the Waikato Journal of Education here) was that many students find the statement 'Physics is a science' difficult. They would rather prefer to re-write it as 'Physics is applied mathematics'.
Now, by science here, I mean a body of knowledge based on a systematic, empirical observation of the world. A body of knowledge that is able to generate testable predictions and then accept or reject or refine hypotheses in light of the results of experiments.
I (too naively) assumed that my audience wouldn't need convincing that physics is a science. Actually, there was some debate on this. One person in particular, a physicist in fact, presented the view that physics is not a science. Biology and Chemistry fit my description of science - being based on experiment - but physics, in its actual outworking, does not. His argument was that the greatest advances in physics have been theoretical and not based on experiment. Quantum mechanics and general relativity are highly theoretical - drawing intensely from mathematics - and any experimental validatiton of them came long after the theory was accepted (and, in the case of Eddington's eclipse data, quite possibly fudged). One might put the Higgs Boson into the same category - I suspect that most physicists never doubted that the Higgs Boson would eventually be discovered. That is to say the physics was not based on experiment - the experiments were merely confirming what physics 'knew' already. Who is the most famous physicist? Albert Eintein - who never did an experiment in his life. But clearly he was a physicist, not a mathematician.
BUT, his was not the only view. For example, Einstein, the theoretical physicist, obtained his Nobel Prize for his explanation of the photoelectric effect. This was an observed phenomenon that had puzzled physicists - results just didn't fit with the understanding of the time. And what about the ultraviolet catastrophe? So theoretical approaches were not made in the absence of experiment - there were some uncomfortable phenomena around that were prompting thinking.
So, back to my point. "Physics is a science" being uncomfortable for students of physics. It is clearly not just students that find this uncomfortable. Is that a reason why, perhaps, the University of Western Australia has now moved 'physics' out of the Faculty of Science and put it in with engineering (which Waikato did many years ago)?
And, if physicists can't agree on what physics is, what hope is there convincing students that they should study it? Maybe I should just surrender and become an engineer.
I came across the following on the BBC website "Australia's summer broke 205 records..." It draws from the recent Climate Council report. The BBC article doesn't list them all 205 of them, but does pull out the most impressive - the hottest summer on record for Sydney, Brisbane and Canberra, and the wettest on record for Perth - a whopping 193 mm.
Let's put 193 mm over 3 months into perspective. Hamilton, NZ, gets (according to metservice.com) 280 mm of rain on average over December to February. A Perth record-breaker would still be called a dry-ish summer back at home. But locally, Perth averages 40 mm over the three months. Also, of that 193 mm, the majority fell in just one day, soon after we arrived here - 112 mm fell on 9 February. That's a pretty wet day anywhere, but it wouldn't be threatning any records back at home.
What I love is the sudden jump in the Bureau of Meteorology's mean February rainfall data. When I wrote my post on 9th February, the mean February rainfall (averaged from 1993 onwards) was 8.5 mm. It now stands at 13.5 mm. When you have low values, averages can fluctuate considerably.
There's been another noticable weather failure for Perth this summer - one that is rather disappointing as a physicist. Take a look at the 3pm wind statistics chart, to be found here. The wind is utterly predictable. At 3pm, it blows from the south west. This is the famous 'Fremantle Doctor' (Fremantle lying southwest from Perth city centre) - a classic sea breeze produced by the rapid heating of the land generating rising air, pulling in the cooler air from the sea. The doctor brings relief from the otherwise soaring temperatures, and makes summer afternoons tolerable.
Except this year. We have experienced very little of the 'Doctor'. It's been rather disappointing, really. Where has he gone to? And will he be back next year?
In a country 'defined by heat', as the climate council report states, climate change is a BIG issue.
As part of our trip southwards last week, we visited one of the many caves scattered across the Margaret River region. The immediate impression on entering the 'Jewel Cave' is its vast size. It's hard to estimate just how big the main cavern is, but as a rough guess maybe 100 metres by 50 metres by 10 or so metres high - probably higher in places. The guide told us we had walked nearly a kilometre on the tour and climbed up and down 500 steps as part of it. There's a lot of volume to it.
The cave was discovered only relatively recently, in the 1950's (from my memory of what the guide said). What drew people's attention to something special was the 'blow hole' on the surface. There is only one natural way into the cave, through a pot hole that's conveniently (for the cavers) wide enough to get a person down, but not much wider. The original explorers had to lower themselves tens of metres down the pothole and then through the cavern, before they touched the ground. We, on the other hand, entered through a man-made tunnel in the side.
This pot hole used to (until the new entrance was built) blow out air or suck in air as the atmospheric pressure changed. A sudden drop in atmospheric pressure outside, for example, would create a pressure differential between the inside and outside of the cave, and the cave would expel air. With a vast volume inside and a pretty tiny hole to come out of, a small shift in pressure can create an intense flow of air at the pothole. it was this extreme flow of air in and out that suggested there was something very big down there, and that this hole was possibly the only way in.
A surprise was also how dry the cave was. The Margaret River region is not a dry area of Australia by any means, but there wasn't a drop of water visible. In fact, the water level has dropped considerably over the last 30 years,without any obvious reason. The cave shows evidence of large changes in water level throughout its history, but why is unclear. There are some hypotheses, such as the lack of a large bushfire above the cave in the last 30 years leading to more leaf litter than might be normal, but the reality is that this is an open research question. There's a lot of science to do here.
Oh, and the biologists can get excited too because there have been thylacine remains found here (Where a human can squeeze, so could an unobservant thylacine).
There's a lot more to this cave than meets the eye.
We put our trust in someone else's calculations and measurements all the time. It's just part of the modern world. Cross a bridge, drive a car, use anything electrical, and we implicity trust that the people who designed it, built it, installed it and tested it have done their job correctly. Occasionally things go wrong and disaster strikes, but, by and large, the things we make use of in our lives work properly.
That said, do you fancy trusting the people who designed and installed the ladder up the Gloucester Tree, at Pemberton?
This was originally built as a fire lookout, amongst the majestic Karri trees of south-west Western Australia. But now it's a tourist attraction. People come to climb it, or to watch people climb it (as we did). I was happy to go up to about rung four, but that doesn't really count.
Now, there must be some trees in Waikato that could benefit from such an addition. And to do so would require a bit of physics and engineering calculation and implementation. I reckon it would be a fantastic project for a student to tackle - pick the right material (please don't poison the tree or choose anything that won't cope with the weather), work out the loading profile, worst case scenarios (e.g. what happens when two large people cross - one going up and one going down), tackle the safety and ethical issues, and so on. And then, to get a grade A+, the student concerned has to be the first to climb to the top!
As if you didn't know already, digging holes is important in Western Australia. And there is a LOT of Western Australia to dig holes in.
Sitting in a park in the centre of Perth is a great collection of stuff that comes out of these holes - the 'Ore Obelisk'. It's a great idea - a geological museum on an impressive scale.
Apoogies for the shoddy mobile-phone camera work. I should really have increased the exposure when taking into the light.
But it's not just those minerals. Witness the 'Synergy Parkland' (yes, I will name and shame one of Perth's largest power companies) in King's Park. There's a lovely children's playground there, sponsored by Synergy, complete with imitation lycopod trees made out of various bits from the electrical generation industry. A great bit of artwork, it has to be said. The explanation says it all. After describing the prehistoric lycopods, the education board says "...and these trees now help us by providing us with coal for power" (or something like that). How lovely to be educating our children to dig up more black stuff and turn it into carbon dioxide.
P.S. Going back to my last post, February 9th reached a maximum of 17 Celsius, with 112 mm of rain. (That is one hundred and twelve, not eleven point two). This is a Perth February day, remember. Normal service has now been resumed.
A quick glance at some climate statistics will tell you that Perth in February is hot, sunny and dry. The mean maximum temperature is 31.7 C for Perth city, with a mean of 7 days going above 35 Celsius, and 1 day going above 40 Celsius.
February rainfall is impressive, by its absence. The mean rainfall for February is listed as 8.5 mm. That rates as not very much at all. On average, just 1 day gets above 1 mm of rain, and 0.3 days (perhaps one February day every 3 years) will get more than 10 mm.
So, here is the weather forecast for the next six days, from australia.metservice.com
Spot the wonderfully high maximum temperature for today. It doesn't look like going above 31.7 Celsius anytime soon.
The person I'm sharing an office with here has told me about an interesting local phenomenon that gives some indication of rain on the way: The river turns brown. Apparantly, in local culture anyway, it's a sure-fire predictor of rain the next day. He wasn't sure what the explanation is, but possibly its the wind churning up the water.
Incidentally, Perth in winter is just as wet as Hamilton in winter. But it is rather warmer!
I have been rather conscious of my looonnnnggggg absence from the blogosphere. That really is down to other commitments getting in the way, and then falling out of the habit of blogging. Hopefully this will be a restart. I have a good opportunity here - I have just started a period of study leave (what used to be called Sabbatical in the old days) and arrived this week in Perth, where I'm visiting the University of Western Australia. I'll be here for nine weeks - a fantastic chance not to be interrupted by people knocking on my door (and, yes, to develop some research ideas too, I should add).
So, first stop, naturally enough when you have a four-year old, is the local playground. And what a playground it is too. It's been set-up to blend in with the trees and it works really well. It also includes a neat bit of physics.
It's a telephone, as in 'tele' (long distance transmission) and 'phone' (voice). Now, the long distance here is only about 10 metres, but it's still quite impressive that it works. The sound waves head down the pipe that you see in the photo, under the ground, then up to an equivalent speaker/microphone across the path. The set up works really well. What we basically have is a broadband acoustic transmission line. Since the pipe is heavy and stiff, the sound waves in the air in the pipe reflect off the sides without too much loss of intensity and out the end. Rather like an optical fibre does for light.
What would be really useful is to add some splitters, directional couplers, multiplexers and the like, which would turn it into something more akin to a modern telephone system and transmit to various different locations. That's one thing that is easier done with electricity or light . One of my PhD students is working on acoustic network analyzers - that's a solved problem with electromagnetic waves but it's not so easy with sound waves, as we're learning.
More Perth physics to follow. Watch this space.
We were away this weekend - in sunny Whakatane. That was a smart move weather-wise. We arrived back home about 2.30pm yesterday afternoon, just as the fog was lifting from Cambridge. An hour later, it was settling down again for the night. A glance at the MetService website shows that, while Whakatane and Rotorua basked in 12 degree maximum temperatures (and somehow Tauranga hit 15 C), Hamilton made it to 7 Celsius.
A consequence of this was that our house was COLD when we came back to it.
Now, those of you who have seen our house will know that it's built to catch the winter sun (pity there wasn't any yesterday) via lots of glass and soak up the warmth with lots of concrete. And it works really well on cold winter days when the sun's out. But on cold winter days when the sun is not out (i.e. Waikato fog) a fundamental design flaw is evident. With no heating on for two days with morning temperatures well below zero, the house got cold. About 7 degrees inside. That was no surprise. The first thing we did was to turn the heat pumps on. An hour later it was still cold. Three hours later it was cold. About six hours later we had the temperature up to 15 degrees. The poor heat pump was blatting out hot air as powerfully as it could, but the house was just not getting hotter quickly at all.
The reason is that concrete again. Just as its designed to soak up the heat from the sun and re-radiate it slowly, keeping some warmth in the evening, so it takes a long time to warm up. Here's a quick calculation.
We have internal concrete block walls about 20 cm thick. Let's suppose they have cooled to 7 degrees. How long does it take (with warm air on both surfaces) to get that concrete back up to temperature? It's a question of diffusion of heat. The heat gets to the centre of the concrete through conduction. This process can be described by the diffusion equation. See here for the lovely maths. The key parameter is something called the thermal diffusivity - often called 'D' - it depends on the thermal conductivity, density and heat capacity of the concrete. For concrete the thermal diffusivity is about 5 x 10-7 m2 s-1. In a time t, heat will diffuse a distance of approximately the square-root of D t. In six hours (about 20 000 seconds), this comes to about 0.1 metres - that is 10 cm. After this time we can consider the middle of that concrete block as having warmed up. Approximately speaking, the concrete wall will then no longer be soaking up the heat from the air, and instead, the air can stay warm.
I have to say that this was about our experience last night. By bedtime, the house was tolerably warm again.
Incidentally, I have also done a quick estimate of the number of kWh of electricity we used last night. Ouch.