January 2009 Archives

This story might be apocryphal; I haven't been able to verify it, but it is certainly plausible.

Mount Egmont National Park forms almost a perfect circle around Mount Taranaki. Given its status, its bush remains intact, unlike the rest of Taranaki. You get a great view of this dark green circle with a mountain poking out of it on a flight from Hamilton to Christchurch, assuming, of course, the weather is good, which is a different matter. Now, I'm told, if you look carefully at a map, you'll see it isn't quite a circle - the boundary has a small kink in it.  (I'm not talking about those annoying extra bits that extend west over the Kaitake ranges that detract from the otherwise perfect cone-shape - it's the circular bit I'm refering to.)

This entry has nothing to do with physics, unless you count the vague link between the subject and satellite imagery. Do forgive me this diversion, which I find interesting and shocking.

At Te Papa Tongarewa, there is a room that is empty, save for a huge (14 metre-long) image of New Zealand on the floor. This 'map' is made from a montage of satellite images of the country. You crawl around on it (literally) looking for where you were born, where you live, where you'd like to live, where you went on holiday etc. It's a superb exhibit - no annotations, no instructions - brilliantly interactive.

I chose to celebrate Auckland Anniversary by visiting Wellington. (Naturally enough.) No surcharges on the coffee there. It was my first visit to the capital as a tourist, and as you might expect I did some of the usual touristy things like Te Papa, Parliament, and the cable car.  The cable car is a real gem; it doesn't cover much height but it's a lovely piece of history, and there's a great cable-car museum at the top. It's a classic funicular design, consisting of two cars connected by a single cable, which is basically wound around a pulley at the top. That means down-ward moving car helps to pull the upward-moving one up. Of course, there's a motor in there too, but the idea is that the two cars are pretty well balanced, so they can be moved without much input of energy.

Water isn't the only fluid that's in everyday experience. Air is as well - the word can apply to either a liquid or a gas. And things moving in air can behave pretty oddly too. I think the best example is an aerofoil - that relies the fact that a fluid's pressure reduces as it moves more quickly (Bernoulli's equation). The top surface of the aerofoil is curved outwards, so the air has further to go, and speeds up a bit as it travels - that means less pressure on the top of the wing and the aircraft rises.

Of course, areofoils were around a long time before the Wright brothers got their hands on them; anyone who has sailed a yacht will tell you that. The sail does the same thing. Being able to sail upwind (or about 45 degrees to it) is a concept that I find rather perplexing, despite having a pretty decent physics training and having sailed dinghys a fair bit. Knowledge of neither the theory nor the practice is quite good enough to get over the impression that travelling upwind just doesn't make sense. Taking the wind's energy, and turning it around to move against the wind, it's just utterly un-natural.

Imagine, if your mind can cope with it, Michael Phelps, decked in his speedos, about to dive into a pool of golden syrup.  If the thought isn't too much for you to cope with, now ask yourself what stroke he should swim to get to the other end as quickly as possible.

As explained in my last entry, Phelps in syrup is kind of like a bacterium in water. Movement is pretty difficult. And it's more than just because it's sticky in there, there is a deep physics reason as to why this should be.  In 'Life at Low Reynolds Number', Edward Purcell explains that movements that preserve time-reversal symmetry will get you nowhere if you have the misfortune to fall into a vat of syrup. Time-reversal what?  Let me explain.

Have you ever thought why water is difficult to move through? What property does it have that air doesn't, that makes it an effort to get anywhere in it?

The answer is utterly straightforward, but it is worth saying: it is simply more dense than air. If you want to move through it, you've got to push the water out of the way, and that means get it moving. And to get something with lots of mass to move requires energy. So it's easier to move through air than water. We call this an inertial effect - i.e. an effect of inertia (mass). But that's not the only effect that can happen with a fluid that will slow you down.

It's summer, and for me that means the university's 50 metre outdoor swimming pool is open. Lots of lunchtime lengths, dodging the morons who can't cope with the concept that lanes are for lane swimming, rather than playing ball games. There's a lot of physics that goes in with swimming. Hydrodynamics, the study of how water flows over something, is big business, and people have written seriously sophisticated computer programmes to work out just how water flows past something.

I guess we all have our own utterly irrational fears. One of mine is needles. It's not that they hurt, because they don't; rather it's the concept that causes me to shudder at the prospect of a blood test. Sticking bits of metal into my body and sucking out the contents? I don't think so. You'll have to catch me first.

Another almost irrational fear is lightning.  We've had quite a bit of it around Hamilton recently, prompting this entry. I say almost irrational because lightning can, and frequently does, kill people. But there are a few very simple things that you can do to pretty-well eliminate this risk.

One tablespoon? Is that all? Depends on the recipe, I guess. But does anyone know exactly how much one tablespoon actually is? The answer, which I found out at the weekend, demonstrates exactly why the world needs physicists.

Last Thursday while browsing a popular NZ-based website an article caught my attention: 'Scientists learn to levitate objects'. Images from Harry Potter films flashed before my eyes, and I thought this had to be something worth checking out. And it was, for two reasons. First, because the article is a surprisingly accurate piece of science writing for  mainstream media, and secondly, it concerns a very curious quantum mechanical effect.

So now you know the first law - what's the second law? This one is a whole lot easier to define since you don't need to fret over what exactly energy IS, and, historically speaking, it was understood long before the first law. (It is relegated to being the second law of thermodynamics since the first law was considered more important).

There are many ways of describing the second law. One highly relevant (to me, anyway) example from yesterday's evening meal at home is 'If you drop a bottle of wine onto the kitchen floor you end up with lots of pieces of glass splattered to all corners of the room - but if you pick up the pieces, place them into a bag, and shake them a bit, they don't reassemble themselves into a wine bottle (to say nothing of the contents)'.  The issue here is that processes that occur on their own are irreversible - they don't undo themselves naturally.

I've used the word 'energy' a lot in recent posts (like yesterday's), but haven't really said what it is. We all have some idea of what energy means - it's a resource you need to do something useful, such as propel a car, or play a video game, heat your house or power refigerator. (This last one is interesting - it can take energy cool something down as well as heat something up - but more on that at a later time). But pinning down what exactly it is is rather harder.

Having lived in Waikato for five years now, I'd forgotten what cold temperatures feel like. I've just got back from Christmas in the UK (explains lack of blog entries) where I was reminded what winter is like: dark and cold. Minus 9 feels pretty nasty, but, how cold is that really?