## Thursday, September 23, 2010

### 2.6g-1 Measurements in Science

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2.6g-1: Measurements in Science: Updated, 14 July 2020
Metric – When the scientists got together in Paris in 1791, first thing was to create a basic unit to replace the measures of the old, bad days; to create a measure of validity based on a natural value that could be checked objectively anytime – permanent, immovable, solid. So they decided to use the curvature of Earth as reference for the basic unit, and they named it "meter" after the French metre, itself deriving from Greek metros – measure. The meter relates to Earth’s meridian, a series of great circles that run along its global surface north-south through the poles and form longitudes on maps. Chief is the Prime Meridian, longitude 00 that runs north-south through Greenwich England. Surveyors, by making measurement along 20 east longitude between Dunkirk and Barcelona, measured the surface distance of the meridian quadrant (1/4 of a meridian circumference of Earth) and took one ten millionth (1/10,000,000 or 0.0000001 or 10 –7) of it and created the meter. (It was not perfectly accurate but, practically, is very close.
For an American, a meter is 39.37 inches or 3 odd inches more than 3 feet. Knowing only feet or inches is only the knowledge of each number but if you know a meter all you need do is multiply by 10 and append 7 zeroes and you have 1/4 of the Earth’s transpolar circumference. Doing it in inches 39.37 x 107=3.937 x 108 inches, and quick mental arithmetic gives Earth's circumference as circa 1.5 billion (1.5 x 109) inches, which computes to 24,855 miles a value. Recent satellite assisted measurements of the transpolar circumference of the Earth give 24,901 miles. Wow! Isn't that a close confirmation of the Scientists of 1791?
The liter is the metric volume. You meet liter as word or suffix very much. Medical lab tests in fluids are reported per liter (or decimal of liter).
The liter is based on the meter. Without seeing a cube, I think everyone knows it is a box with 6 equal square panels of 6 equal sides. A liter is the capacity of a cube whose sides are 1/10 of a meter, or a decimeter (dm), so the formula for volume of cube (side x side x side) gives cubic decimeter for 1 liter. As with all metric units the liter is expressed in 10-unit groups; in the downward direction, eg, 1/10 liter = deciliter, 1/100 liter = centiliter, 1/1000 liter = milliliter. Stop here! “Milliliter" (ml) is the most frequently used unit of volume. Our bodies have 5,000 ml of fluid blood, or 5 liters.
The liter is 1.06 quart.
The cubic relation of meter to liter is seen in the common measurement unit cubic centimeter (cc) which is equal to milliliter (ml). How is this? Recall 1 liter = 1 cubic decimeter, or dm3, and there are 10 cm in 1 dm so substituting we get 1 liter = (10 cm)3 . Then 1 liter, which is 1000 milliliter = 1000 cm3, so 1 ml = 1cc. Strictly, the “ml” should be preferred but “cc” is common.
In the U.S., blood tests are reported in concentrations of grams (g) or milligrams (mg) per liter (l or L) or per deciliter (dL or dl).
An important household dose for fluids is teaspoon (5 ml) and tablespoon (15 ml).
The gram is used to measure weight. One thousand grams are 1 kilogram (kg) which weighs c.2.2 pounds avoirdupois (libra, or lb). One pound weighs c.455 grams or 0.455 kg.
A milligram of fluid since it has density near 1 gram per ml is about 1 ml. Thus 1 cc or ml of fluid weighs c.1 mg. Even solids can be roughly estimated this way, and since a teaspoon and a tablespoon is 5 ml and 15 ml, 1 flat teaspoon of sugar weighs slightly more than 5 mg, and 1 flat tablespoon, 15 mg. This is useful for home dosing when no other means of measure.
I should like to head off confusion in the conversion of grams to the common American and British fluid and weight measure “ounces” (oz). If you are working with a weight, like in powders, it is in the avoirdupois system which is 16 oz = 1 lb, and 1 oz = 28.375 g but if you are working with fluids, 1 fluid ounce = 1.04 avoirdupois ounce. And note the obsolete (Troy) system where 12 apothecary oz = 1 lb, or 1 apothecary oz = 37.833 g. With fluid measure, always use “fluid oz” or else confusion will be sparked.
Today in 2019, the meter, the gram and the liter as well as the seconds of time are defined by standard measures kept at Sevres France. That's the metric system.
END OF THE SECTION. To read on now, click 2.7 The Periodic Table of the Chemical Elements