All entries for Friday 21 January 2005

January 21, 2005

The campaigning begins

Writing about web page http://www.sunion.warwick.ac.uk/portal/voting/Default.asp?url=ELECTION_CANDIDATES&election_id=1005

The list of candidates for the Union's primary elections is out! Note that most candidates will not upload their finalised manifestos until the Monday deadline.

Three bloggers and a current Sabb are among those going for President – definitely a strong field. One or two of the other positions are a little more clear-cut in terms of realistic choices, but then the current batch of Sabbs is the first in the last 3 years in which all or nearly all of the best candidates actually won. Union elections are funny old things sometimes.


Waster

Writing about News for consumers: Stuff is getting cheaper from Neighbourhood #1

Well I'm on a roll tonight! Two very different branches of my engineering degree employed in the space of 1000 words and about 2 hours. Anyway, this is a reply to Iyobosa, who is happy at a BBC report on the trend for consumer goods to be ever-cheaper while the cost of repairing them is rocketing. I'm glad the BBC article also hints – slightly – at the appalling waste of resources that results from this.

If consumers demand the absolute minimum price for an item, manufacturers will seek to cut corners to produce their budget model. This breaks down after a year, or 6 months, but hey, it's cheaper to throw it away and buy a new one than get the old one repaired.

Suddenly there's an increasing market turnover of this item – instead of buying one and using it for 15 years, repairing it maybe twice in its lifetime, consumers will see it break and replace it within three, as it's the cheaper option. Why, therefore, should the makers manufacture something engineered for more than a 5 year lifespan? That would waste them a lot of money.

Now you're in a situation where people are happy to buy the latest model of this item, use it for a short period of time and then throw it away. Even if you could set up a multi-multi-million pound scheme to recycle all of the materials, you've still lost the resources consumed in producing the energy to manufacture the product in the first place.

The 100% recycling concept isn't practical anyway. It would be a massively expensive process, consuming lots of energy and man-hours. The process is often not even possible, particularly when the product is engineered for ever-cheaper production costs, e.g. with snap-fit fastenings instead of screws. If the product is never going to be repaired, there's no need to design a means by which it can be taken apart easily!

Household waste in the UK is growing faster than the economy; our recycling rates – around 12% of domestic waste – are about the lowest in Europe. Britain's landfill sites are literally filling up (some counties have very nearly no space left) and, as waste needs to be dumped further and further afield, more and more diesel is used in transporting it there.

All of this helps explains things such as the new EU Directive known as WEEE (Waste Electrical and Electronic Equipment), and talk of lots of extra taxes on companies and hence individual products, but it still does not give sufficient voice to why the increasingly prevalent use-and-dispose ethos in our society is such a bad thing.


A splash in the pan

Writing about Things I'll never understand [part II] from Michael - Dutiful Bandsaw

Michael asked a question about peeing. I suggest you read his question before you read this response, unless you are very, very easily offended, in which case browse elsewhere for today.

——-
Before I start, note that a urethra is a urethra either way and so this will also apply to ladies. Girls may not poo (a well-known fact), but they definitely pee, often in large groups when they're in a bar.

Most engineering students would be able to tell you the answer here. edit: Or so I thought. I had to spend quite a while on this and may still have missed something more obvious...

I'll attempt to put it simply but explain it fully. I hope even non-scientists will be able to follow this. This is not something I'd like to do a thesis on by the way, Michael. (But then I'm not a fluid dynamicist, thankfully).
——-

Fluid dynamicists are obsessed with non-dimensionalising everything so that their equations will work for any type of fluid, flowing at any speed, through a channel of any size or under any other variations of conditions.

The first non-dimensional number you learn in Fluids is the Reynolds number, which combines the viscosity and density of the fluid, the flow speed and a "characteristic length" – the size of a flow channel, or of the obstruction in the flow you're looking at (e.g. an aircraft's wing thickness). In this case, "width of channel" is more appropriate. We can assume here that channel size, flow velocity and viscosity and density of urine are similar for all men. And women.

Now, in an ideal world, flow is nice and smooth (think of a tap turned on just enough that you get a steady flow). However, no real pipe is perfectly smooth and this certainly applies to a biological tube such as the urethra. Above a certain Reynolds number (approximately 2000 for pipe flow), flow becomes unstable and prone to turbulence. Roughness can trip a smooth flow into turbulence, and this is what happens when you pee. If you pee faster you'll notice that the flow becomes more turbulent, as the Reynolds number increases with velocity.

At normal peeing speed, the flow is on the point of turbulence, we've established that. But what about the corkscrew? That's a result of the surface tension of the liquid keeping the molecules in a steady stream. This is a viscous effect.

Now back to your whisky bottle: the fluid is probably similarly viscous and dense. The bottle's neck is smoother and certainly wider(!) than in the first example, but you're also pouring much faster. Thus you're replicating similar conditions, so are at a similar Reynolds number and see a similar flow regime.

Note that the Navier-Stokes equations which describe fluid flow are not soluble by anybody in the world at the moment. Some more pessimistic fluid dynamicists have suggested that mathematically they may never be solved (merely approximated to very well).

The Coriolis Effect – a hideously complicated phenomenon arising, I believe, from centripetal acceleration as a result of the earth's rotation – appears on a significant scale mainly for applications such as predicting weather patterns (i.e. fluid flow in the atmosphere). It doesn't have any real effect in this case, and certainly not on bathwater when you pull the plug out!


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