Dear Euric and All, The number 97.28 kPa looks interesting.
I wonder whether the space station engineers originally decided to use atmospheres as their air pressure unit, and then decide to pressurise the space station interior at 96�% of one atmosphere. The number, 97.28 kPa, looks a lot like it is a euphemism for 96% of 1 atmosphere of 'standard pressure '. Sadly, '96% of 1 atmosphere of 'standard pressure ' involves three layers of conversions with their attendant approximations. If this is true it seems a fairly cavalier way to approach the lives of the space station astronauts. The calculation might look like this: A 'standard pressure' of one atmosphere is 101.325 kilopascals and this in turn is an exact conversion of the old measure, 760 millimetres of mercury. To reduce internal forces on the space craft you then reduce this by (say) 4�% to 96�% of 1 atmosphere (0.96 x 101.325 = 97.272 kPa and we then round this up to 97.28�kPa) These numbers and the conversion calculations are interesting because they reveal how some groups go about their metric transition. In the case of air (and other gas) pressure there are many groups such as: aerosol chemists, engineers, meteorologists, pilots, and steam train drivers. All of these traditionally used their own particular units for measuring gaseous pressure, and perhaps more importantly, each of these groups had a set of 'rules of thumb' that they used to guide their work. Of these the most convenient 'rules of thumb' are the average (which might be the mean, the median, or the mode) and the range. Consider the mass of new born babies. The first thing that happens to a modern baby is that its mass is determined in kilograms so that if it becomes critically ill in the next few days it can be treated by modern drugs that are dosed in millilitres per kilogram or micrograms per kilogram, and all of the professional medical staff need to know the baby's mass. However, the baby's mother is more interested in the comparative mass of the child compared to her mothers, her sisters, her cousins and her aunts babies, and so, ignoring the potential threat to the health of her baby, she insists on converting the baby's birth mass into pounds and ounces to see where the baby fits in the range of babies as reported to her by her relatives. None of her relatives are aware that a 3.5 kg baby is about average; that a 2.5 kg baby is small; and that a 4.5 kg baby is a whopper. Notice what's happening here. The metric conversion is driven by professionals for good and rational reasons that are concerned with the health, and even the life, of the babies in their care. But others involved in the process (mothers, grandmothers, sisters, cousins, and aunts) want to meet other (social) obligations and to do this they insist on keeping the rules of thumb that have operated well for them in the past. So let me return to people who use pressure units. New mothers are not alone in their seemingly irrational behaviour - professional engineers often work in a similar way. Eventually all pressure workers will use micropascals, millipascals, pascals, kilopascals, or megapascals for their daily work, but as they make the metric transition they will try to take their rules of thumb with them. They will not immediately create new rules of thumb to suit their changed circumstances. For example, when the scientific pressure workers converted from millimetres of mercury to atmospheres, they took their (rounded average) with them by simply converting 760�mmHg to 101.325 bar exactly. Whether there was an actual, real, physical basis for the seemingly rounded value, 760�mmHg , I don't know; it certainly looks like an approximation that was an aide memoire or a rule of thumb to remind people where the average sat - approximately. Again, as pressure workers moved to metric measures the 760�mmHg took many forms, amongst these were: bar, bar abs, g/cm^2, g/cm^2 abs, mbar, mmHg abs, psi abs, psig, psig vac , and various kinds of torr. Notice how the metric transition did not seem to drop many units (if any) but resolutely kept the old in parallel with the new. It is my view that this is done so that pressure workers can keep their old rules of thumb while giving lip service to the forces of metrication. The behaviour that I have described here obviously leads to a slower metric transition. If you are involved in a metric transition in your group, your company, your industry, or your nation, I suggest that you give some careful thought to the rules of thumb that guide your current work and devise ways that these can be part of your metric transition. Cheers, Pat Naughtin LCAMS Geelong, Australia Pat Naughtin is the editor of the free online newsletter, 'Metrication matters'. You can subscribe by sending an email containing the words subscribe Metrication matters to [EMAIL PROTECTED] -- on 18/1/04 1:50 PM, Chimpsarecute at [EMAIL PROTECTED] wrote: > http://www.abc.net.au/science/news/stories/s1024569.htm > > Pressure aboard the station had been slowly dropping for several days and on > Monday morning stood at , Russian space officials said. > > After the crack was sealed, pressure climbed back up to 97.28 kPa, which is > considered normal, they said. > > > The US press has been reporting this leak in PSI. > > The BBC didn't mention the exact pressure loss other then: > > "The leak is in a flex hose in the lab window," he said by telephone. "It's > 95% at this stage... It is most likely the culprit". > > Maybe they didn't want to use kilopascals but wasn't sure of the conversion to > FFU, so they didn't print any numbers. > > > > > I was wondering if anyone knows what units are used by the crew of the space > station. My understanding is that the American contribution is FFU and > contributions from the rest of the world are metric. Why this hasn't resulted > in some sort of disaster is beyond me. > > From the ABC article there is only the mention of the American on board. I'm > not sure of the nationality of the other crew member. He could be Russian. > With an international crew aboard the likelihood of the units of measure being > SI increases then if it strictly an American crew. > > Euric >
