Sunday, 15 August 2010

Tube or False (or just nonsense)

There is a new advertising campaign on the London Underground... I'm not entirely sure what it's advertising, as everyone who sees the posters is already on the Tube and presumably already aware that it exists. Anyway, the campaign is entitled Tube or False, and consists of 8 statements about the system for us to guess whether they are true or false.

One of these is:
Every week, our escalators travel the equivalent of 2 times round the world. 
I'll post a spoiler under the fold, but pause for a second to decide if you think that's plausible.
Done that? Did you actually pause to decide if the statement was plausible? If so, did you notice that the statement is not only not plausible, it's entirely meaningless! Before we look at why, I'll quote the answer from the tfl website:
It's true…and it's easy to see why. There are now over 400 escalators on the network which run for 20 hours a day, 364 days a year - so you can imagine how they can achieve such great distances.
Presumably they got their numbers like this:
 400 escalators x 20 hours x 1mph = 8000 miles/day x 7 days = 56000 miles

The Earth is roughly 24000 miles round, so this isn't far off. However, we should probably do a little bit of dimensional analysis. What are the units of our final answer? We have escalators x h x m/h, which is... erm... escalator-miles. I'm not actually a physicist, but I don't think "escalators" qualifies as a dimensionless quantity.

To see how absurd this number is, imagine that one day someone decides to come along and divide every escalator on the Tube into two pieces of exactly half the length (probably as part of a fiscal stimulus or something). Now we have 800 escalators, travelling at the same speed for the same amount of time, which will presumably go 5 times round the world - and yet nothing has changed!

In fact, if we're going to use this absurd method of measuring how far the escalators go, why limit ourselves to counting escalators? Why not measure individual steps? There's probably about 100 steps per escalator, so we could say that "every week the steps on our escalators travel the equivalent of about 200 times round the world". Why stop there? "The atoms in our escalators travel the equivalent of about one octillion times round the world".*

I guess 250 miles of track just doesn't sound impressive enough...

Incidentally, as I'm writing about TFL, and as Andy wasn't aware of it despite being one of about three people who regularly read this blog, I'm just going to take this opportunity to repeat the fact that you can get discounted fares when using your Oyster card if you have a Young Person's Railcard.

* I realise this number is probably several orders of magnitude out, but it makes the point, and I can't be bothered to get it right.

1 comment:

T_Beermonster said...

"Every week, our escalators travel the equivalent of 2 times round the world"

This is manifestly false. The earth rotates once per day and there are seven days per week.
Their escalators travel 7 times round the world in a week unless they are doing very strange things to space and time. Though that may explain a few other things...