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.

When the power goes off - Physics Stop

Aug 20, 2019

This morning we woke up to discover  a power cut. This meant: No electric kettle. We do have a gas stove, however, which we could light with the help of matches (the automatic ignition relies on mains power.) So we did eventually get some hot drinks. No toaster. No microwave. No hot toast, no porridge. Back to the Weetbix. No hot water. The gas instant water heating relies on electricity for the ignition. So no shower. No heating. Obviously the heat pump and panel heaters don’t function, but neither did the gas fire. It needs electricity for ignition and control. No internet. The modem needs electricity. No landline phone. Ours is connected through the fibre network, which needs electricity. No mobile phone. Out of charge. No automatic garage door. and the list goes on… My point is that so much … Read More

The lying dashboard (part 2) - Physics Stop

Aug 14, 2019

Following-on from my suspicions as to the accuracy of my car’s reporting of my travel statistics, here’s another mystery. The length of my journey from home to work, as recorded by my odometer this morning, was 24.7 km.  The length as recorded by Google Maps is 25.2 km.  So, my odometer underreads. Or it did this morning, anyway.  But the car overreads my speed. If it gets the speed from revolutions-of-the-wheels data, one might expect that an overreading speedometer implies that the speed is being calculated based on a larger tyre circumference than actually exists. That makes sense with my current tyres, which are getting close to needing replacement. (Yes, they are still legal). But then, assuming the odometer also goes off wheel revolutions, I’d expect that to overread too. But it showed less than Google Maps. Now, also, … Read More

Student evaluations of teaching effectiveness tell us nothing about teaching effectiveness - Physics Stop

Aug 12, 2019

I thank my colleague Chris Lusk for bringing this paper by Uttl, White and Gonzalez to my attention. Many universities and polytechnics acquire Student Evaluation data on courses and teacher quality at the end of a course. There are different ways this can be done – here at The University of Waikato students are asked (online) a series of questions about the course and teaching of the course to which they can ‘Agree strongly’, ‘Agree’, ‘Disagree’, or ‘Disagree strongly’.  They can also provide free-response feedback on the course. It is the quality of these student evaluations that is the subject of the research of Uttl et al. They present a large meta-analysis (i.e. a combined analysis of lots of peoples’ data) on the extent to which the scores that university students give to their teachers in end-of-semester evaluations relate to … Read More

The lying dashboard - Physics Stop

Aug 07, 2019

How accurate are our car speedometers? That’s well discussed., e.g. on this AA question forum.  If the ‘expert’ here is correct, your car speedometer could over-read by as much as 10% + 4 km/h (which is quite a bit – if you are doing 45 km/h it might read 54.5 km/h, or if you are doing 90 km/h it might read 103 km/h). But it should never under-read speed. So, when I travel through the Tamahere roadworks  and the large “Your speed is…” sign tells me I am doing 48 km/h, I should not be surprised that my speedometer is reading 55 km/h. (OK, you ask, when can you ever travel through the Tamahere roadworks at 48 km/h? Fair point. Answer: about 9:15 am this morning. Child number two is sick today and I was rather late in to … Read More

Quantum cryptography - Physics Stop

Jul 30, 2019

I was reading last week a children’s book about “Secret codes”.  You probably know the kind of thing I’m talking about – substituting one letter for another, or a squiggly shape for a letter, rearranging letters, and so on. Fun things to do, but not the basis of modern cryptography. However, the book didn’t just stop at these codes, but went on to talk about some of the modern principles of cryptography, trying its best to keep it understandable to (say) a ten year-old. For example, there’s the box with two padlocks.  How do I send a secret message to my friend, keeping it secure? I can lock it in a box – that will keep it secure, but then I have the problem of how I send a copy of the key to the box to my friend. The … Read More

Language in physics teaching - Physics Stop

Jul 23, 2019

Hello everyone. It’s been a long while since I was blogging, but I am back again now. The second-half of the year is rather less hectic for me, so I have some time to get back to this. I’ve been considering recently the learning that students have achieved in our first year paper “Physics in Context”.  This is a paper designed for students who haven’t done a lot of physics. We have collected various bits of data from this paper, and one of the clear messages is the difficulty students find in expressing physical understanding in words. For example, “what do I write down in my lab notebook?” was a question that cropped-up time and time again throughout the course. It is really difficult for students to articulate their understanding. In some cases, this is because the vocabulary of physics … Read More

Measuring the temperature - Physics Stop

Feb 22, 2019

I’ve just bought some thermometers, to use with a first-year physics class. A box of ten of them. Alcohol filled, which makes them a whole lot safer than the mercury ones. (If you have a mercury thermometer, my advice is never, ever break it, especially if it’s at home. I broke one at university a few years ago – at least we had the ability to clean it up properly – but most homes won’t.) Anyway, a little test as to how good they are. What is the temperature in my office? They are graduated in whole degrees Celsius, but I reckon I can read them to the nearest half a degree. Here are the readings (in degrees C), after they have all been sitting next to each other on my desk for a while: 24.5, 25.5, 25.0, 24.0, 24.0, … Read More

Alice the camel - Unsorted

Feb 05, 2019

As we drove on a family outing at the weekend, we sung “Alice the camel”.   For those who don’t know it, it goes like this (to the tune of “Dem Bones”): “Alice the camel had five humps; Alice the camel had five humps; Alice the camel had five humps; so go, Alice go! Alice the camel had four humps… Alice the camel had three humps… Alice the camel had two humps… Alice the camel had one hump… Alice the camel had no humps; Alice the camel had no humps; Alice the camel had no humps; so Alice is a horse (of course!)” Only when you have a gifted six-year-old in the backseat, it doesn’t stop there: “Alice the camel had minus one humps… And we got up (or should that be down?) to about minus nineteen humps before the song … Read More

Why you shouldn’t eat beef - Physics Stop

Jan 11, 2019

“Don’t eat beef.” Such a statement does not go down well in New Zealand,  especially in Waikato, where the cow reigns supreme. I don’t say it as someone who wants to peddle a “Meat is Murder” message. I don’t believe that at all. I say it as someone who wants New Zealand to take Climate Change seriously. Quite simply, producing a serving of beef produces a staggering amount of carbon dioxide, as the diagram here from Poore and Nemecek (2018) demonstrates: [Source:  ; original data from: Poore, J. and Nemecek, T. (2018). Reducing food’s environmental impacts through producers and consumers. Science 360, 987-992. DOI: 10.1126/science.aaq0216  ]This might need to be put into more context.  Driving 100 km in my car produces something around 14 kg of carbon dioxide.  One serving of high-impact beef tops this. Even a low impact serving of … Read More

In praise of fixable appliances - Physics Stop

Dec 17, 2018

Last week saw the first ‘fault’ on our washing machine. We’ve had this particular one for nine months, and with a baby and young boy in the house it is well used. When I went into the laundry to empty the machine I found the cycle had not finished as I had expected. Instead, the machine was flashing an error code at me. You know the ones. The kind that laugh at you and say “Ha! You’ve overworked me.  I’m on strike. You’re going to need to get someone in to look at me. It’s going to be pricey. And just before Christmas too; in fact, you might have to wait till the New Year before I’m back working again. Oh, and don’t get any ideas about being able to open my door and recovering your clothes – I’m locking … Read More