Overview: Why Measurement?
The earliest systems of measurement used natural phenomena such as the rotation of the earth (day), phases of the moon (month), and the seasons of the year. Units of measurement soon became standardized, often to the measurements of the king. For example, King Henry I decreed that the yard was the distance from his nose to his thumb. As travel and commerce became more frequent, and scientists needed more precise measurement, an international system with standardized measurements became a necessity.
Detour to the English System
The English system of measurement is most widely used in England and the United States. Units of measurement include the familiar 12 inches in a foot, three feet in a yard, 5280 feet in a mile for length; 2 cups in a pint, 2 pints in a liquid quart, 4 quarts in a (US) gallon for volume; and the confusing measurements for ounces, pounds, hundredweights, and tons. Those literally depend on what weight is being measured — whether it is a standard weight, a troy weight, or a commercial weight, and whether it is in the United States or Great Britain.
The Metric System
In the late 18th century, the French Academy of Sciences developed an international system that was based upon precise measurement. The meter is 39.37 inches long, and the basic units of measurement for length are derived from the meter, in decimal form. The millimeter is 1/1000 of a meter; the centimeter is 1/100 of a meter, and the decimeter is 1/10 of a meter. In addition, the decameter is 10 meters; the hectometer is 100 meters; and the kilometer is 1000 meters. Weight is measured by grams, and volume by liters. One liter was originally a cube with edges 10 centimeters long; and one gram is the weight of one centimeter square of water at 4 degrees Celsius. That is also the size of one milliliter of water. The same prefixes as for length are used for weight and volume, so that a milliliter (ml) is 1/1000 of a liter, and a kilogram is 1000 grams (2.2 lbs.). The metric system is used in most countries of the world, including in the United States, for scientific and many commercial uses.
Temperature
The earliest temperature scale to develop was the Fahrenheit scale, in which water freezes at 32 degrees and boils at 212 degrees. In the Celsius scale, water freezes at zero and boils at 100 degrees. The Kelvin scale was developed and used for scientific purposes. Absolute zero, the point at which all molecular motion stops, is -273.15 degrees Celsius. The degrees on that scale are the same size as the degrees on the Celsius scale.
Conversion
Until all countries in the world use the metric system, it is important to be able to convert units from one measurement system to another. For example, one meter is 39.37 inches, or a little over a yard. One kilometer is 3/5 of a mile, so to convert kilometers to miles multiply by 3 and divide by 5. One kilogram is 2.2 pounds. One liter is about 1.1 quarts. To convert Fahrenheit to Celsius, subtract 32 degrees from the Fahrenheit temperature, and divide by 1.8. To convert Celsius to Fahrenheit, multiply the Celsius degrees by 1.8 and then add 32.
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