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A PHYSICIST WRITES . . .

(January 2017)

Well, another year has rolled by, leaving me with various stories (relating to physics or motoring) which I didnít have space to cover within my ten columns in 2016. This first one teaches a lesson that scientists and others learn the hard way sometimes. And it might have affected a few of you: last August it was revealed that a ďsmall numberĒ of households and businesses, maybe 10,000, had been receiving erroneous gas bills, some for up to 15 years!

How so? In most cases, what had happened was that an old Ďimperialí meter measuring gas in cubic feet (though actually reading in 100s of cu ft) had been replaced by a new one reading cubic metres Ė but the change wasnít recorded properly by the supplier. Or else the consumer had switched suppliers, and the wrong type of meter had been assumed by the new company.

Now 100 cubic feet = 2.83 cubic metres. So these gas bills were either nearly three times too high, for readings from a metric meter that was assumed to be imperial, or nearly three times too low where an old one was still in place but was thought to be metric.

It seems incredible that in the whole chain of people from meter-reader to bill-checker (thatís if there is anyone in between, or even the latter person at all?) no-one picked up the error, or rather, these 10,000 errors, sooner. And itís equally surprising that some consumers didnít complain when their bills suddenly increased! They are of course in line for a refund (if not paid already). Whereas the lucky fewer who were undercharged wonít have to pay the difference...

By the way, measuring the volume of gas is only the first step in calculating your bill: next a Ďcorrectioní is made for temperature and pressure (though as itís the same adjustment for everyone, and at all times of year, I donít quite see the point). Then the figure is multiplied by the energy per unit volume, or calorific value, of the gas Ė thatís to say, the average value for the gas you have been supplied with. (But how do they know what this is? Your Ďsupplierí could be at the other end of the country, hence not pumping into the network any of the actual gas you were burning.)

The calculation produces the amount of energy you have supposedly consumed, and then finally this is converted into kilowatt-hours: an absurd unit for gas, except that when you compare its price with that of the same unit of electricity-energy, you can see immediately that gas is around four times cheaper!

But letís return to the subject of confusion between imperial and metric units: as I said, sometimes the lesson to avoid this has to be learnt the hard way. In 1999, after a nine-month voyage, the NASA spacecraft Mars Climate Orbiter arrived at its destination, and was steered into orbit. Unfortunately, one part of the control system calculated the necessary thrust in pounds, but another part assumed it was in newtons (the metric unit). The Orbiter orbited all right, but much too close to Mars, burning up in its atmosphere. As did the $328m mission cost.

An Air Canada internal flight in 1983 could have ended even more disastrously: the airline had just switched from pounds to kilograms for calculating the fuel needed for each journey Ė but the ground crew for this flight took the figure to be in pounds still, and so less than half the amount of fuel was loaded. Also, the on-board fuel gauge had failed (really!). When the engines suddenly stopped, by good fortune the pilot was able to glide the aircraft down to a nearby airfield.

Closer to home, in fact surrounding you whenever you drive, are codes in the format 205/55R16. They are of course the markings on your tyres. Donít ask me why, but the 205 is the width of the tyre in millimetres, whereas the 16 is the diameter of the wheel-rim in inches. You might think that this too could be some sort of recipe for disaster, though I havenít come across an example of it. Also, Iím glad to say that I donít recall making an embarrassing mistake with units in my own career (though my memory could be letting me down).

But hereís another sorry story, of a different sort of mix-up though again about fuel, which I heard privately rather than via the media: someone agreed to look after his friendsí car during their holiday (after dropping them off at the airport). On his way to meet the return flight, in their car, he did the decent thing and filled the tank for them. Alas, he put in petrol, whereas the engine would have much preferred diesel...

I canít resist mentioning a report from 2016 that tempted me to think that my columns are read in high(ish) places. The RAC Foundation commissioned some research on permanent average-speed cameras to find out (a) how widespread and (b) how effective they were. The answer to the first question was that they covered (at the time) already more than 250 miles of UK roads, over distances ranging widely from a fraction of a mile up to 98 miles Ė this extraordinarily long stretch being on the A9 in Scotland.

As for their effectiveness, it was demonstrated beyond doubt that accident rates (particularly for fatal and serious collisions) had fallen sharply wherever the cameras were installed! So let me just quote what I wrote here more than ten years ago: ďWhatís needed is a pair of linked cameras at each end of any road where there is a speeding problem, so that when a number-plate was recognized as having travelled from one end to the other too quickly (in relation to the speed limit), a penalty would be automatic.Ē Admittedly I was thinking more about how speed humps might be done away with, but itís nice to see that my solution was a good one.

Something else I advocated in 2006 was aiming to maintain a constant speed when in a slow queue of traffic, rather than matching the stop/start behaviour of the vehicle ahead. Hence I was pleased last year to catch up with research (over a long period) by an American motorist with scientific inclinations: on congested multi-lane highways, he had found that he could smooth out the disruptive flow in his lane for a long way behind, in comparison with the other lanes (and as viewed in his rear mirror from the crest of a hill), by adopting a steady speed and creating a decent gap in front, which meant that he rarely had to brake.

There are other advantages too in driving in this manner, for you and everyone around you. So take a look at the manís website, www.trafficwaves.org, and spread the benefits!

Peter Soul

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