The following is an email I sent to the group that writes a daily column, "Good Morning Lowcountry" (aka GMLc) in our daily newspaper.
They took a shot at explaining millibars but had the impression that those were the current metric units --- or at least implied that by omission of the pascal. They also let it be known that they were lacking in knowledge about the newton. Rather than berating them, I took the tack of applauding their effort and suggesting some small corrections. Honey, not vinegar.... Jim ---------- Forwarded Message ---------- Subject: Slight correction on your column for October 25 Date: Tuesday 25 October 2005 20:29 From: "James R. Frysinger" <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Dear GMLc, Your column today reviewing the hurricane season was excellent, yet it deserves a little bit of cleaning up. Thank you for using metric units to express the air pressure in the eyes of hurricanes. Unfortunately, you used an obsolete metric unit. Worse, so does the National Hurricane Center in its public statements, so I suppose that lets you off the hook just a wee bit. The current standard (Federal Meteorological Handbook No. 1, FMH-1) calls for the reporting of sea-level air pressures in hectopascals instead of millibars and it has since 1996. The current version (2005) can be found at http://www.ofcm.gov/fmh-1/fmh1.htm It turns out that pressures in hectopascals (the modern unit) are numerically equal to pressure in millibars (the obsolete unit). This is probably why American meteorologists chose to use the hectopascal rather than the kilopascal as do meteorologists in other countries. Thus, nobody needs to learn "new numbers", only the change in the name of the unit. By the way, as you probably know, based on your knowledge of common SI prefixes, 1 kPa = 10 hPa = 1000 Pa. The National Weather Service does work in modern metric (SI) units, but they convert their reports to non-metric units (such as inches or millimeters of mercury and such as degrees Fahrenheit) because they assume that Americans prefer non-metric units. That is rapidly becoming a bad assumption. Let's talk about the newton (not "Newton" as you wrote it) for a moment. The newton (N) is the SI unit of force. Weight is a force and one can calculate the weight of things by multiplying their masses (in kilograms) by the local acceleration due to gravity. A convenient value for the latter (which varies from location to location and even with the state of the tide!) is 9.8 N/kg, or just under 10 N/kg. So, for example, a 100 g apple (a medium-sized one, in other words) has a weight of about one newton (1 N). The pascal is the SI unit of pressure and 1 Pa = 1 N/m2 (one newton per square meter---that "2" is supposed to be a superscripted exponent). Turn that 100 g apple into applesauce and smear it over a square meter (about 16 sheets of copy paper in area). The pressure that applesauce exerts on that area is thus about 1 Pa. Normal atmospheric pressure at sea level is considered to be 101 325 Pa or 101.325 kPa or 1013.25 hPa. (Think of this as the equivalent of about 100 medium apples, turned into applesauce and smeared over one square meter of floor space.) Remember, unit names are never started in uppercase unless they are the first word in a sentence. Unit symbols start in uppercase if the unit was named after a person and also (in the US) in the case of the liter (L). A colleague and I have spent nearly two years up to this point reviewing all new and IEEE standards (e.g., the ones for WiFi, cell phones, firewire, ...) and revisions to those standards to make sure they correctly use the SI, which is the modern metric system. I would be glad to answer your questions in the future so that you don't have to look things up. Again, thank you very much for your effort to improve the knowledge of your readers about the metric system. Please let me help you to make sure that the modern one, the SI, is the one that is explained and not an obsolete one. best regards, Jim Frysinger -- James R. Frysinger Lifetime Certified Advanced Metrication Specialist Senior Member, IEEE http://www.cofc.edu/~frysingj [EMAIL PROTECTED] [EMAIL PROTECTED] Office: Physics Lab Manager, Lecturer Dept. of Physics and Astronomy University/College of Charleston 66 George Street Charleston, SC 29424 843.953.7644 (phone) 843.953.4824 (FAX) Home: 10 Captiva Row Charleston, SC 29407 843.225.0805 ------------------------------------------------------- -- James R. Frysinger Lifetime Certified Advanced Metrication Specialist Senior Member, IEEE http://www.cofc.edu/~frysingj [EMAIL PROTECTED] [EMAIL PROTECTED] Office: Physics Lab Manager, Lecturer Dept. of Physics and Astronomy University/College of Charleston 66 George Street Charleston, SC 29424 843.953.7644 (phone) 843.953.4824 (FAX) Home: 10 Captiva Row Charleston, SC 29407 843.225.0805
