Wikipedia gives mathematical models vs latitude and altitude: http://en.wikipedia.org/wiki/Earth's_gravity (Scroll down about 75% of article length, after city values.) Be aware there are also local microgravity variations, which can be significant in some applications.
--- On Tue, 9/29/09, Pat Naughtin <[email protected]> wrote: From: Pat Naughtin <[email protected]> Subject: [USMA:45922] Re: The plummet in metric history To: "U.S. Metric Association" <[email protected]> Date: Tuesday, September 29, 2009, 5:08 PM Dear Bill, I think that you are right in saying Jefferson used a pendulum with a period of 2 seconds for his 'seconds pendulum' with a length of about a metre. Others, particularly Prieur in France, used a pendulum about 250 mm long to give a period of about 1 second. By the way, do you know of a reliable web source where I can find the values of g, the acceleration due to gravity, for various places around the world? When I searched, I found a lot of physics teachers with good values for their class room locations – but little else. Only one of these gave a (calculated) value for the North Pole (9.8640 m/s^2) and the equator (9.7982 m/s^2); see http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Gravity/AccOfGravity.html This reference at http://wiki.answers.com/Q/Which_Europe_Cities_have_exactly_9.80665_MS_of_acceleration_due_to_gravity doesn't help much! http://mtp.jpl.nasa.gov/notes/altitude/altitude.html states that 9.80665 is the gravity at sea level at 45.542 degrees latitude, and one might assume that the definition was intended to be what it is at 45 degrees exactly. I assume what you're really asking is how was 9.80665 chosen, and this should answer that. But anyway, major European cities within a degree of 45N: Bordeaux, Lyon Turin, Milan, Belgrade, Bucharest. Cities along this line of latitude on other continents: Novorossiysk, Krasnodar, Halifax, Green Bay, Minneapolis, Portland. Cities near 45S: Dunedin (NZ). Rawson (Argentina). Cheers, Pat Naughtin Author of the ebook, Metrication Leaders Guide, that you can obtain from http://metricationmatters.com/MetricationLeadersGuideInfo.html PO Box 305 Belmont 3216, Geelong, Australia Phone: 61 3 5241 2008 Metric system consultant, writer, and speaker, Pat Naughtin, has helped thousands of people and hundreds of companies upgrade to the modern metric system smoothly, quickly, and so economically that they now save thousands each year when buying, processing, or selling for their businesses. Pat provides services and resources for many different trades, crafts, and professions for commercial, industrial and government metrication leaders in Asia, Europe, and in the USA. Pat's clients include the Australian Government, Google, NASA, NIST, and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com for more metrication information, contact Pat at [email protected] or to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter to subscribe. On 2009/09/30, at 02:31 , Bill Hooper wrote: On Sep 28 , at 7:14 PM, Pat Naughtin wrote: Dear All, Does anyone know anything of the history of the 'plummet'? As the plummet was in common use in 1812, my question relates to how long before 1812, this pendulum method was in use for military marching. If this technique was available in 1790, for example, then it would have had a significant influence on the metric debate about whether to use the plummet pendulum or the size of the meridian as the basis for the length of the metre. This debate centred around Borda who wanted to market his 'repeating circle' and Thomas Jefferson who favored the pendulum method because of its universal availability and its portability; That's interesting, Pat. I had heard that Jefferson's efforts were the reverse; namely, that the second should be defined as the time of the half period of a pendulum of some specific length. If the second is defined as the time for the half period of a simple pendulum (on Earth, etc.) with a length of exactly 1 m, then (using the modern definition of the metre) the second would be 1.0035 seconds (of the currently defined kind). If the currently defined second would be used to define the metre, the metre would be 0.9929 metres (of the present kind). Bill Hooper 1810 mm tall (using the presently defined metre) or 1797 mm if the metre were defined in terms of the pendulum. Fernandina Beach, Florida, USA ========================== SImplification Begins With SI. ==========================
