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.

A cracked window - Physics Stop

Jan 08, 2021

On Christmas Eve, child number 1 spotted a crack in a window. It’s a double-glazed window, and inspection showed that the small, horizontal crack was in the outermost pane. It was perpendicular to the frame, about three-quarters of the way up one side. The origins are a mystery. It MIGHT have something to do with repeated encounters with footballs, tennis balls (usually flying off the face of a cricket bat), rugby balls, frisbees and the like. Or it might be a thermal stress – this window gets full sun in the early morning. Over the next few days, this crack grew, in quite an interesting way. It always grew at night. We never saw any discernable growth in it during daytime, but each morning of the next few days the crack was longer than it had been the night before. Read More

The difference between science and engineering - Physics Stop

Dec 23, 2020

I’m often asked what the difference is between science and engineering. Or, put another way, why did I find working in a ‘School of Engineering’ when I’m a physicist (i.e. a scientist) so difficult sometimes? (I now work in  ‘Te Aka Matuatua – School of Science‘ at the University of Waikato.) The two disciplines blur a bit at the edges, and there can be substantial overlap between them. But, broadly speaking, I’d say a scientist is interested in how processes work, and why they work, and what might be done with them, whereas an engineer is concerned with making them work. Here’s an example in the news recently: nuclear fusion. This has to be the Holy Grail of energy generation. Basically, if we can get nuclear fusion happening in a controlled way on Earth, we have a near … Read More

Kane Williamson’s ‘soft hands’ - Physics Stop

Dec 16, 2020

I had the delight of being at Seddon Park on Friday 4 December, watching Kane Williamson on his way to 251 runs. It was a wonderful innings to watch and he’s a perfect example to try to copy if you’re learning to play the game. Part of his success is down to his ability to defend superbly. He’s able to play the ball really late, to the point that its almost frightening to watch from square on from the wicket: you think the ball has got through his defenses and is about to hit the wicket when suddenly, at the last possible moment, the bat comes down on it and the ball drops harmlessly at his feet. By playing late on it, he ensures the bat is angled backwards so that there is no chance of the ball popping upwards … Read More

Repairing a hole in the wall with the diffusion equation - Physics Stop

Nov 20, 2020

Last week child number 1 managed to put a hole in a plasterboard (‘gib’) wall. I wasn’t in the room at the time, but I believe it had something to do starting at one end of the house,  running down the corridor, through the bedroom doorway, doing a forward flip onto the bed and sliding feet first into the wall at the end of the other end of the house. Unfortunately, the house isn’t built for gymnastic floor routines. So we’ve been repairing the wall. Actually, it’s not that difficult to repair a hole in plasterboard, so long as it is only a few centimetres across.  Secure a bit of mesh into the hole (get that at the DIY shop or make your own out of wire) and build up layers of wall filler. Then sand it back to be … Read More

Fancy coughing at your phone? Nicer than a swab up your nose - Physics Stop

Nov 03, 2020

The pandemic has certainly been a trigger for some really interesting science to be done. Here’s something that’s hit the headlines today – Artificial Intelligence can be used to detect COVID-19 from the sound of someone’s cough. If you want to read it, the full report is here, but unless you’re lucky enough to subscribe to IEEE you’ll only be able to read the abstract. A game-changer in the fight against COVID-19? Hard to say right now, but it certainly has potential. The sensitivity of the algorithm is impressive: 98.5% overall, and 100% for people who don’t have symptoms. That means there’s the potential for nearly everyone who has COVID-19 to be identified. One can easily imagine the potential of this. Perhaps not so much for New Zealand*, but in a country where a great many people have … Read More

Scholarship Physics - Physics Stop

Oct 16, 2020

It’s that time of year when school students become seriously focused on exams. This year has been messy for student learning, and has affected some students more than others, but the NCEA external assessments and the Scholarship exams are going ahead pretty-much as normal. I’ve taken some interest in the Scholarship Physics exams over the past years. It’s an exam that’s intended to flush out the very best physics-thinkers in the country, and award them appropriately. A student who does well at scholarship physics is one who doesn’t just know physics, but can ‘think’ physics. They can recognize physics principles and apply them in unfamiliar situations and talk critically about what they are doing. In other words, a student who gets Scholarship Physics is demonstrating what a real physicist does. And that’s why I like the exam. Read More

When analogies are taken too far: Spacetime is bent, but it’s not quite a stretchy membrane - Physics Stop

Sep 30, 2020

Last week I was asked by some school students about the nature of gravity. What is it? Isaac Newton, and a whole pile of textbooks following him, treat gravity as an attractive force between two objects. It’s a force that is proportional to the product of the masses of the two objects, and is inversely proportional to the distance between the objects squared. That is, F = G M m / r^2, where M and m are the masses of the two objects and r is the distance between them. The constant G, known as Newton’s Constant of Gravitation (or ‘big G’, for short), is given by  6.6741 x 10-11 m3 kg-1 s-2, with an uncertainty of about 5 in that last digit. ‘Big G’ is really hard to measure well, and its value is far more uncertain than … Read More

Friction and the Anti-lock Braking System - Physics Stop

Sep 22, 2020

Yesterday afternoon I had to call on my car’s anti-lock braking system (ABS). For reasons best known to its driver, a car pulled out of a side road right in front of me while I was driving home after work, and I needed to stop in a hurry. I rather think the car behind me had to rely on its ABS too, to avoid hitting me. I don’t think I’ve ever had to brake that hard in this particular car before. The crunching noise the ABS makes and the vibration in the brake pedal certainly took me by surprise, even though I knew that’s what it does. The ABS allows the brakes to operate to maximum effect by controlling the braking so that the wheels are just at the point of slipping, but not beyond. The video shows the … Read More

Post-communist Bulgaria, solar eclipses, and NZ Level 2 restrictions - Physics Stop

Sep 01, 2020

In August 1999, I had the opportunity to travel from the U.K. to Varna, Bulgaria, on the Black Sea coast, to view the European Total Solar Eclipse. Just why we ended up in Varna, as opposed to a plethora of other possibilities in Europe, is a bit of a long story, but a substantial part of it was a near guarantee of cloud-free, Black Sea summer. The eclipse itself was fantastic. Unfortunately, unless you are very lucky, you will need to travel to see a total solar eclipse. That said, New Zealand, which is currently in a bit of a solar eclipse drought (there’s a tiddly partial visible in the south of the South Island at the end of next year), will experience monsoon eclipse conditions in 2028. In the subsequent 17 years, it will get three total … Read More

Bad light stopped play - Physics Stop

Aug 26, 2020

One of the top challenges for physics in the modern era, along with Climate Change and explaining Dark Energy, has to be fixing the problem of bad light*. (I’m talking cricket – what else?) It’s a quintessentially English problem. It’s not raining, the pitch is perfectly playable, the spectators (COVID-19 notwithstanding) are enjoying themselves, but the umpires bring the teams off because they deem the conditions unplayable. So the second test between England and Pakistan manages only a day’s play out of five – partly because of rain but also because of Bad Light. It’s frustrating, but at a professional level it really is a safety issue as much as one of fairness. I’ve done my share of amateur 20-over-a-side cricket games squashed into that short period between finishing work and sunset, and, late in summer particularly, the last … Read More