Marcus Wilson

Dr Marcus Wilson is a lecturer in the Engineering Department at Waikato University and author of the Physics Stop blog. His current research involves modelling of the electrical behaviour of the human brain during natural sleep, focussing particularly on the transitions between sleep states. Previous research interests include infra-red physics and signature control (stealth) and quantum Monte Carlo methods. He graduated from Cambridge University in 1992 (BA Hons) and completed his PhD at Bristol University in 1995.

More to sundial than meets the eye - Physics Stop

Mar 22, 2017

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 deciphering 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 sundial is actually telling the correct time. The answer was usually ‘no’. Even when a sundial is … Read More

Physics is a science. Or maybe not. - Physics Stop

Mar 14, 2017

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 … Read More

Weather records - Physics Stop

Mar 11, 2017

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 … Read More

Jewel Cave: Blowing potholes - Physics Stop

Mar 07, 2017

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, … Read More

Trusting someone’s engineering calculations - Physics Stop

Mar 03, 2017

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 … Read More

Physicsstop back in business - Physics Stop

Feb 07, 2017

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 … Read More

Video: laminar flow, microorganisms and mangroves - Physics Stop

Jun 21, 2016

This movie is a demonstration of laminar flow. My colleague Julia Mullarney used it last week in our Osborne lectures to high-school students to demonstrate what turbulent flow ISN’T. Video showing Laminar Flow and demonstrating fluid flowing in layers. This apparatus was developed by John DeMoss and Kevin Cahill of the Department of Physics & Astronomy, University of New Mexico.   Basically, laminar flow is time-reversal invariant. This implies a few things, but, notably here that if you reverse the processes involved you get back to where you started with. Motion of micro-organisms This is the problem that micro-organisms face when they move. Any motion that has time-reversal symmetry (like a swimmer kicking their legs, or a scallop shell opening and closing) will get them nowhere. The solution for the micro-organism is to rotate a flagellum (or … Read More

Probability madness - Physics Stop

May 10, 2016

Probability crops up in many places in physics, not least quantum mechanics and statistical mechanics where we are only sure of things in an average or ‘statistical’ sense. Dealing with probabilities can be a headache for many students. They are also a headache for many in everyday life. There are numerous occasions where we need to estimate the likelihood of something occurring and we can get it very wrong indeed. What is the probability of encountering a monster traffic jam on the way to Auckland Airport – just how early should I leave for that flight?  What are the chances that my visitor will actually turn up on time – or at all?  Bookmakers make their living on estimating probabilities so it’s always amusing when they get it wrong (I have deep issues with gambling). According to the odds First, … Read More

The universal joint - Physics Stop

Mar 10, 2016

…No, it isn’t something everyone smokes…  But it is common in machine mechanisms. The universal joint is a neat way of turning rotation in one plane into rotation in another. A common use is on driveshafts where you want the direction of the shaft to bend. There’s a neat animation on Wikipedia of how the thing moves. Despite seeing them in action (including in our teaching lab) I’m always amazed that it works. Let’s think about it. There are four pins on the joint – two for one shaft, and two for the other. They have to stay in the same geometry (namely at the four corners of a square) as both shafts rotate. That doesn’t seem possible. Three points are what defines a plane – put in a fourth and surely it’s not, in general, going to … Read More

The storm surge - Physics Stop

Feb 26, 2016

I shudder to think what it must have been like in the path of Cyclone Winston. It is hard to conceive of winds 230 km/h sustained for minutes at a time. I remember vividly what is now known as the Great Storm of 1987 (an extra-tropical cyclone) which pulverised south-east England on 15/16 October 1987. There were (according to Wikipedia – ahem!)  gusts close to 200 km/h recorded in Sussex (where I lived), but there were possibly higher ones than these – the anemometers failed. I spent the night listening to trees falling one by one around our house. Opposite the house was (and still is) a very tall Wellingtonia – one of the earliest specimens of this tree planted in the UK – and if that had fallen on us there wouldn’t have been much house … Read More