The University of Waikato - Te Whare Wānanga o Waikato
Faculty of Science and Engineering - Te Mātauranga Pūtaiao me te Pūkaha
Waikato Home Waikato Home > Science & Engineering > Physics Stop
Staff + Student Login

Recently in science Category

There is no denying it. I am middle-aged. The latest evidence is the progressive-lens glasses. I had tried to put off getting these for as long as possible (warning to you younger readers - they are not cheap!) but it was just getting too difficult without them.

We pretty-well take for granted good vision, but most of us can only enjoy really good vision by virtue of really good lens-making methods. In my case, while my vision was fine while at school, it became apparant rather quickly at university that mine wasn't as good as some of my friends. Sat at the back of one of the large lecture theatres I really couldn't kid myself that I had good eyesight. I couldn't read what was on the screen at the front, while others around me could. While my vision isn't so bad that I'd walk into things without my glasses, or be unable to read bus numbers on the front of buses*, I'm obviously short-sighted, meaning that I can happily look at things close to me (up to a couple of years ago, anyway), but far-off objects just can't be focused.  In terms of the physics of my eye, the focusing is mostly done by the cornea (which I don't have control over), and then a little by the lens. Muscles squash or stretch the lens in order to focus an image - a squashed lens is more powerful than the unsquashed lens and focuses the image closer to the lens**.  But in my case far away objects are focused in front of the retina and I can't stetch my lenses enough to bring the image into focus onto the retina. To correct this, I need diverging lenses in my glasses. 

But that's not all there is to it. I also have astigmatism, meaning that my corneas are not rotationally symmetric. They have different focal lengths for objects at different orientations. This means the lenses in my glasses need to have different strengths in different orientations.  

Unfortunately, now that's not all there is to it either. My lenses (the ones in my eyes) can't squash and stretch as much as they used to. This means that, despite being near-sighted, I now have trouble reading. For close-up work, I need a (slightly) converging lens. That's awkard - diverging for distance, converging for close work. Some people manage that by having two pairs of glasses, but since in my work I am constantly switching between close-up work and long-distance work and mid-distance work it would make for a logistic nightmare. Some people have bifocal lenses (including a small piece at the bottom for reading, but the rest of the lens the usual prescription). And some have progressive lenses. 

Progressives are rather neat and as a physicist I find it amazing that they work in practice, as well as in theory. Here the idea is that the power of the lens varies gradually from the top of the lens (which is diverging) to the bottom of the lens (slightly converging) - including the astigmatism correction as well. A consequence of an all-in-one lens is that not all the field of vision can be sharp at once. If I look out the sides of my glasses, things are a bit blurry. But one has to remember with vision that the brain is just as important as the eye. Although the blurriness is there (it was very apparant when I first put the glasses on) after a few weeks of wearing them I just don't notice it any more. Where I want to look is always in focus, and that's what counts. 

And that's made switching my gaze between books, computer screens, visitors in my office and the view of Mt Te Aroha from my office window a whole lot easier. 

 

Notes.

*The same couldn't have been said of my father. He was very myopic (short sighted). His mother discovered this when my Dad was very young, following a conversation that went something like this.

Dad (about 4 years old, waiting with my Grandmother at a bus stop). Mummy, how do you know which bus to get on?

Granny: Because we can look at the timetable which tells us which number buses go where, and the times they go. So to go home from the city, we need a number 12 bus. 

Dad: Yes, but how do you know which bus is a number 12 bus?

Granny: Because it has a big '12' written on the front of it. 

Dad: Where?

 

**Contrast this to the way a camera focuses. With a camera, the lens is of fixed power - to focus the lens moves closer to or further from the sensor. 

| | Comments (0)

At the recent NZ Institute of Physics conference in Dunedin we heard about a wide range of different physics topics -measuring electrical forces; atomic frequency combs; why a highly gendered physics class is not a good thing and measuring forces with your phone. 

One very simple but thought-provoking presentation was by Tim Molteno - on sycamore seeds and their properties as little wind turbines. As far as I understood it, Tim's work here was a follow-up to what his son Linus had done as a science fair project. 

If, like me, you grew up amongst deciduous woodland, you'd have enjoyed playing with sycamore seed helicopters. They can fall very slowly indeed, giving the seed chance to drift in the wind away from its parent tree and get some chance of seeing some daylight when it germinates. It's pretty easy to measure the properties of a seed (it's weight, how fast it falls, and so on) at home and therefore do some basic wind-turbine calculations to see well the seed performs at slowing down the passing air (relative to the seed) and creating a lift force on the seed.  Tim and Linus have done this - and very well too - with a really careful consideration of uncertainties.  This last bit is important because the results show that the seeds are right on a fundamental limit (the "Betz limit") for their efficiency - that is, they are as efficient as a turbine could be.  

But they should not be - conventional wind turbine theory says that this limit can only be reached with a high tip speed ratio (the ratio of the tip speed of the blade and the wind speed). But the sycamore seed doesn't have a particularly high ratio and so its efficiency should be rather lower.  So one could say that these seeds are breaking the laws of physics.

Well, no, not quite.  What is more likely is that our understanding of turbine theory is lacking. Fluid flow can be very complicated indeed (ask an America's cup yacht designer) and some of the assumptions made in constructing the theory may not quite be correct.  Interestingly, the sycamore seed sits in the transition zone where the fluid flow isn't fast enough to be considered turbulent, but not really slow enough to be considered laminar and there might be some very complicated physics going on.

So, then, should make our electricity generating wind turbines the size and shape of sycamore seeds?  We would need a lot of them!

| | Comments (0)

....is about 2 cm long and lives behind the heat pump unit in the courtyard outside.

She's been out every evening since we got here. Can anyone identify her? She doesn't appear to feature on Western Australia's most deadly list (which, incidently, includes the white tail).  I've left it till after we've left to post this just in case someone tells me she's deadly. Ignorance is bliss..

P1090434 (2).JPG

| | Comments (0)

The Institute of Physics has just released a report on recent interventions designed to improve the uptake of physics at 'A'-level by girls*.

Although there have been considerable efforts in the UK to improve the gender balance over two decades, there has not been any substantial change - about 20% of a typical A-level physics class is female. Why is this.

In the latest study, three different methods were trialled. While they all had modest impact on their own, a much greater effect was observed when all three methods were used together.

You can read the details in the report, but briefly, the three approaches were as follows:

1. Developing girls' confidence and resilience. Previous research had found that boys often consider their own successes as being down to their own hard work and skill, whereas their failures were down to some external influence (it wasn't MY fault I did badly...). Girls, however tend to do the opposite - they see success as down to something outside their control and failure a result of their own lack of ability. This strand helped address this - for example girls were given the opportunity to go into primary schools and help with science lessons and to tackle real science projects in industry. In short, create the understanding that "Yes, I can do physics".

2. Working with physics teachers in the classroom. There are many things that go on in the physics classroom to create bias towards boys. Just skim through a typical physics textbook and you'll see many of them - photos of famous and not-so-famous physicists - nearly all of them male. Examples of physics taken from football, snooker, cricket and other male-dominated sports. Boys often dominate classroom discussions. Often teachers can show unconsious bias in their physics teaching towards boys. In this strand the researchers worked with the teachers so that they could see biases and correct them. 

3. A whole-school approach tackling gender stereotypes. Previous work had shown that the type of school made a big impact on girls' uptake of physics at A-level. This approach worked with the schools on equity policies (and how they played out), engaging with both staff and students, including networking and careers events and talking with groups about big issues such as domestic violence.

All three approaches were a little bit successful on their own. However, by far the biggest impact was at the six schools where all three were used simultaneously. Here, the uptake of A and AS-level physics by girls went from 16 students (in 2014) to 52 (in 2016).

This work was not without challenge, however, The report also concluded that it was absolutely important to get buy-in from senior-leadership within the school. Without that, room for improvement was limited. There are many reccomendations (you can read them yourself), but the overall message I interpret as this:

Yes, the gender imbalance can be improved. That has been demonstrated. But we will not achieve this across the board without substantial effort across the whole physics and teaching community.

 

*I use the words 'girls' and 'boys' here since these are the same words used by the Institute of Physics to describe females and males under the age of 18. I apologise in advance if readers believe that 'women' and 'men' would be better words here.

| | Comments (0)

Only a week more to go in Perth. Time here has gone so quickly. It's then off to UK for Easter to see my family before returning to Waikato.

On Saturday we had a tour of the bell tower on the waterfront. It's a great looking structure (in my opinion) - and houses the original peal of bells cast for St Martin-in-the-Fields in London. Just how they came to Perth is a bit of a long story, but they had to be removed from St Martin's because they were too heavy and were causing serious structural damage to the tower. Now they have a new home, along with a great many other bells. Collectively they are called 'The Swan Bells' - in Perth naming something is easy - just put 'Swan' in front of whatever it is.

We had a go at bell-ringing. Not the St Martin's bells, but some others. You've probably seen bell ringing on television - people energentically pulling down on ropes and letting them go - as the bells swing back and forth. We didn't get to that stage. We just swung them gently and got them ringing.

The experience was a quick tutorial in inertia and resonance. First of all, to get a bell swinging takes some force. Pulling the rope creates a torque on the bell, but a large bell doesn't accelerate very quickly. One has to be patient. Once it is swinging a little, by pulling at the right time one can add to the amplitude of the oscillation. That's resonance - applying a driving force at the right frequency. 

But a gently-swinging bell doesn't sound. The reason is that the clapper is moving with the bell. To get it to sound, we need to get the clapper to hit the bell. The way to do that is to stop the bell and let the clapper keep swinging. Now, that's hard work. This time we had to pull down on the rope before the bell reached its maximum displacement (i.e. as the rope was still going upwards). It did feel rather like I was going to be heading up with the rope towards the ceiling, but it didn't happen. But it took some force to bring the bell to a sudden stop and cause the clapper to run into it.

The final bit of physics was apparent on listening for my bell ringing. It wasn't easy to pick out which bell was mine from among the other five or so bells ringing at the same time, because I heard the sound a short time after tugging the rope to stop the bell. That I think  was mostly down to the time taken for the clapper to run into the bell once the bell has stopped. There would also have been a short delay for the sound to travel from the bell to the bell ringer several metres away, but I suspect over that distance it would have been barely perceptible.

Some bellringers can keep going for three hours at a time - and make sure their bell sounds in the correct, constantly changing sequence too. That must be some impressive feat of physical and mental endurance.  Finally, a photo (that I took a few weeks ago) of the Swan Bells in action - at the hands of the experts.

IMG_20170212_134845.jpg

 

 

| | Comments (0)

A couple of days ago I arrived 'home' to discover our local ant colony at work. There's a nest located somewhere in the bushes at the front of our temporary home, and the occupants have become rather adept at raiding our kitchen. Anything left on the kitchen bench is fair game for the taking. Ants are amazingly strong for their size - any little bit of food like a small oat flake gets picked up and transported back to the nest.

Now, in this case the ants were after the grated cheese. Some sizeable flakes had been left on the bench and these were going to be a feast for an ant colony. By sizeable I mean something you get from a coarse grater - perhaps 3 mm wide and maybe 2 cm long. Now, to get them off the kitchen bench and to the nest, they had to take them across the bench, up the splashback by the sink, across the windowsill, out of the window and then down the wall outside. Getting them across the bench was no problem for a few tough ants - all heave together - and away goes this piece of cheese. Quite amazing to watch them move it so quickly.

But the next bit was tricky. They had to manoeuvre the cheese off the bench and up the wall. They did it by putting one end of the cheese against the wall - then a group of ants on this end slowly lifted it up - while a group on the other end pushed. At least, that's what it looked like they were doing. It seemed to be a touch random, but, on average, that's what was happening. Once the cheese had a bit of an angle to it, it got easier, since it was able to rest there, supported on one end by the friction of the wall, and the other end by the bench. Very soon it was on its way up the wall.

Watching them at work reminded me of the 'ladder on the wall' problem. This is a problem in statics that's often wheeled out to bring the over-enthusiastic "I can solve everything with equations" student back down to the earth with a thud. "A ladder of length 4 m (or whatever) and mass 10 kg (or choose your own) rests at an angle of 80 degrees against a vertical wall with coefficient of static friction 0.8.  The bottom end is resting on the flat ground with coefficient of static friciton of 0.6. (a) Draw a free-body diagram showing the forces acting on the ladder. (b) Evaluate these forces."

The point here is that this problem, as phrased, does not have a unique solution. I'll let you have a go at drawing out the freebody diagram. There's the weight of the ladder (which we know), and we can assume that acts downwards at the centre of mass. That bit is easy. At each of the two ends we have a normal force from the surface and a friction force. That's five forces in total. We know the weight, so it leaves us four to find.  But we can only find three independent equations - we know in equilibrium that (1) the horizontal component of force must be zero, (2) the vertical component of force is zero and (3) moments about the centre of mass are zero. Four unknowns, three equations. We can try to take moments about some other point, such as the ends of the ladder. But that doesn't yield any more information. In equilibrium, the coefficients of friction don't help us find new equations (just inequalities). We are stuck. This is called a 'statically indeterminant problem'.

Now, there are ways of proceeding (the enthusiastic student can read this, for example), but we need to know some more information about the elastic properties of the ladder, the wall and the ground. But my point is that there are some seemingly simple physics problems that just can't be tackled by a naive throw-the-equations-at-it approach. We do need some more careful thinking.

I reckon the ants were not too interested in the finer points of statics when they were manouevring this piece of cheese. In the same way, one doesn't need to solve statically-indeterminant problems in order to safely use a ladder. But, for a physicist, it begs the question "What is the coefficient of friction between a piece of cheese and a tiled wall when the surface is lubricated with ants? And then, "Is there a good way of modelling this?"

 

| | Comments (0)

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.

IMG_20170208_133053.jpg

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.

 

 

 

 

| | Comments (0)

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.

 

 

 

 

 

 

| | Comments (0)

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.

 

 

 

 

| | Comments (0)

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?

P1090221saved.jpg

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!

 

| | Comments (0)