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.

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

A battery charge meter that actually works - Physics Stop

Aug 11, 2020

If you drive an electric car more than trivial distances between charges, you likely appreciate a state-of-charge meter (that is, what would be called a fuel-gauge in a petrol car) that is accurate. When it reports a range of 30 km, you do want to be sure it will actually do this distance. If you run out of fuel in a petrol car, you can get a lift to the nearest petrol station, fill up a can of petrol, return to your car and get going again. With an electric car you need towing. But there are numerous problems. How quickly your battery discharges will clearly depend on how you drive the car. An estimate of range will make some assumptions about how you are driving, and in what kind of conditions. That’s true in a petrol car too. Better … Read More

The Beirut explosion shockwave - Physics Stop

Aug 06, 2020

That was clearly a huge explosion. Just after the explosion, we see a cloud of ‘fog’ moving outwards at high speed. This is a shockwave, rather similar to that which causes a sonic boom. The ‘fog’ is caused by water condensing from the atmosphere in areas of intense low pressure and temperature, and parallels the sonic boom cloud, or vapour cone, such as in this photo. The shockwave consists of a front of extremely high pressure, caused by compression (squashing) of the air, which is followed by a region of very low pressure where the air has been stretched. When air is rapidly expanded, it cools. Feel the nozzle of a compressed aerosol spray next time you use one. It will be cold. The resulting cold, low pressure air cannot hold as much water vapour and … Read More

All-pervading Waikato dampness - Physics Stop

Jul 17, 2020

Yesterday we arrived back in Cambridge after a few days holiday in Auckland, being tourists. We sampled such delights as the unheated hotel swimming pool,  the complicated and expensive process of getting on a bus (basically having to find somewhere from which to buy a HOP card, for a non-refundable $10 a card), the completely non-social distanced pedestrian rugby scrum while navigating the building site outside Britomart, and the incessant foggy-drizzle of Tuesday that rendered the beautiful view of the city from Devonport utterly invisible. Returning on the now-open Huntly bypass gave me a view of some Waikato countryside that I hadn’t seen before. And passing wetland-after-wetland in the pouring rain reminded me that much of this wonderful region of Aotearoa is swamp. In winter, one cannot escape the fact that Waikato is damp. We then face the usual dilemma … Read More

Pass the pigs – ad (almost) infinitum - Physics Stop

Apr 20, 2020

I warn you, this post will make little sense to anyone who doesn’t know the game Pass the Pigs. What do you do on a damp Easter Holiday Monday? (Not that the Holiday Monday bit makes much difference in our house…) Play Pass the Pigs of course. And what do you do when you’re a physicist who’s finished playing Pass the Pigs? You decide to work out the optimum tactics. It’s not just down to luck – the skill is to know when to ‘bank’ your points and when to keep continuing, risking a Pig Out that will lose your points for that go.  To optimise the strategy, you need to know the probabilities of getting the various combinations. Fortunately, there’s a seven-year-old in the house who is learning about percentages and plotting bar graphs and pie charts. So, … Read More

Expanding houses - Physics Stop

Apr 08, 2020

It’s  a beautiful autumn afternoon, we need to get out of the house, and so our bubble sets off on a bike ride around our local neighbourhood, Cambridge Park. The bikes come out of the garage, and, being really certain we have a front door key, close the garage door again. And off we go. A while later, having been up and down and around just about every street in Cambridge Park, having spotted a hundred teddy bears, ten chalk murals on fences, and witnessed (sadly) more than one driveway drinks party (NO!), we arrive back home, dismount our bikes and unlock the door. And try to open it. And try to open it. No… this is not a good time to be shut out of your house…And, after a bit of shoving, finally get it to shift. The … Read More

Eight new COVID-19 cases today. It’s no surprise when you look at some numbers - Physics Stop

Mar 18, 2020

So, as I sit at home with a very, very slight headache (i.e. not at work when I would otherwise be so), the now familiar figure of Ashley Bloomfield reports eight new confirmed cases of COVID-19  including two in Waikato. A surprise, given that we had just twelve yesterday? No. A worry? Maybe, but no more so than it was yesterday. Here are some numbers to make the point. All the cases today are imports – recent arrivals from overseas. Let’s try to estimate the probability of any arrival from overseas carrying the virus. Western Europe has a population of roughly 500 million (depending on which countries you count), and, according to the latest WHO bulletin, have confirmed about 60 thousand or so cases of COVID-19, around half in Italy. That’s roughly speaking about 1 person in eight … Read More

Delays in feedback: Learning to drive, brain waves and COVID-19 - Physics Stop

Mar 11, 2020

With the numbers of new COVID-19 cases in China diminishing by the day, China now faces a problem. How to get the country back to work, or partly back to work, or more back to work, without taking too many risks with the virus taking off again. The risk can’t be eliminated, except by shutting its borders altogether and eliminating the possibility of re-imported cases, but it will likely look to find the best balance of productivity and risk. Basically, it’s successfully pushed stage 2 of an outbreak back into stage 1,  as Siouxsie Wiles puts it, and will want to keep it that way while still being productive as a country. But changing the way that the outbreak is managed is problematic. The effect of a change in management won’t flow into the figures for several days. When … Read More

A beginning of semester corona-rant - Physics Stop

Mar 04, 2020

I’ve had enough of COVID-19 now. No, I haven’t had it (well, not that I’m aware of), what I mean is I’ve had enough of reading misleading headlines, hearing xenophobic attitudes and dealing with outright selfish behaviour. Let me elaborate: Point 1 We know that every outbreak will be accompanied by a kind of tsunami of information, but also within this information you always have misinformation, rumours, etc. We know that even in the Middle Ages there was this phenomenon. – Sylvie Briand, WHO Health Emergencies Programme. (Quotation sourced from The Lancet, here). And the New Zealand media are no exceptions here. At the weekend I saw headlines along the lines of “COVID-19 more deadly than SARS, MERS” and “I’ve had coronavirus: It’s not that bad“.  What’s wrong with the first? Well, it depends on what you mean by … Read More

Mucky rain - Physics Stop

Feb 20, 2020

While the south of New Zealand has been struggling with too much rain in recent days, here in the north we are so very short of it (though Saturday’s forecast looks promising).  Basically, we have had almost none since Christmas. As someone who relies on rain to wash the car, this means my car is now looking rather mucky. The carwash at the petrol station I use most is not in action any more – I don’t know whether that is to save water or for some other reason – so this means I might actually have to get a bucket or two of water and clean the thing myself, while trying to keep water use to a minimum. (Yes, I know that sounds like a totally selfish perspective and please be assured I don’t actually rate the state … Read More