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From Wikipedia

Metric system

The metric system is an international decimalised system of measurement, first adopted by France in 1791, that is the common system of measuring units used by most of the world. It exists in several variations, with different choices of fundamental units, though the choice of base units does not affect its day-to-day use. Over the last two centuries, different variants have been considered the metric system. Since the 1960s the International System of Units ("Système international d'unités" in French, hence "SI") has been the internationally recognised standard metric system. Metric units are universally used in scientific work, and widely used around the world for personal and commercial purposes. A standard set of prefixes in powers of ten may be used to derive larger and smaller units from the base units.

The International System of Units is the official system of measurement for all nations in the world except for Burma, Liberia, and the United States. (Some sources identify Burma or Liberia as metric, however.) However, a number of other jurisdictions have laws mandating or permitting other systems of measurement in some or all contexts, such as the United Kingdom – where for example the Traffic Sign Regulations (TSRGD) only allow distance signs displaying imperial units (miles or yards) – or Hong Kong. In the United States, metric units are widely used in science, military, and partially in industry, but customary units predominate in household use. At retail stores, the litre is a commonly used unit for volume, especially on bottles of beverages, and milligrams are used to denominate the amounts of medications, rather than grains. Also, other standardised measuring systems other than metric are still in universal international use, such as nautical miles and knots in international aviation.

Overview

One goal of the metric system is to have a single unit for every physical quantity; another important one is to avoid the need for conversion factors when making calculations with physical quantities. All lengths and distances, for example, are measured in metres, or thousandths of a metre (millimetres), or thousands of metres (kilometres), and so on. There is no profusion of different units with different conversion factors, such as inches, feet, yards, fathoms, rods, chains, furlongs, miles, nautical miles, leagues, etc. Multiples and submultiples are related to the fundamental unit by factors of powers of ten, so that one can convert by simply moving the decimal place: 1.234 metres is 1234 millimetres, 0.001234 kilometres, etc. The use of fractions, such as of a metre, is not prohibited, but uncommon, as it is generally not necessary.

However decimal time is not used. Submultiples of the second (the microsecond for example) are used in scientific work but for lengths of time greater than a second traditional units (minutes, hours, days ...) with their non-decimal conversion factors, are almost always used rather than, say, "megaseconds".

In the late 18th century, Louis XVI of France charged a group of experts to develop a unified, natural and universal system of measurement to replace the disparate systems then in use. This group, which included such notables as Lavoisier, produced the metric system, which was then adopted by the revolutionary government of France. On 13 July 1790 Thomas Jefferson presented a document Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United Statesto congress in which he advoated a decimal system that used traditional names for units (such as ten inches per foot). The report was considered but not adopted by Congress.

In the early metric system, there were several fundamental or base units, the grad or grade for angles, the metre for length, the gram for mass and the litre for capacity. These were derived from each other via the properties of natural objects, mainly the Earth and water: 1 metre was originally defined as of the distance between the North Pole and Earth's equator as measured along the meridian passing through Paris, the kilogram was originally defined as the mass of one litre (or, equivalently, 1 dm3) of water at its melting point (this definition was later revised to specify a temperature of 4 Â°C). The Celsius temperature scale was derived from the properties of water, with 0 Â°C being defined as its freezing point and 100 Â°C being defined as its boiling point under a pressure of one standard atmosphere. The metre was later redefined as the length of a particular bar of platinum-iridium alloy; then in terms of the wavelength of light emitted by a specified atomic transition; and now is defined as the


From Encyclopedia

English units of measurement

English units of measurement principal system of weights and measures used in a few nations, the only major industrial one being the United States. It actually consists of two related systems—the U.S. Customary System of units, used in the United States and dependencies, and the British Imperial System. The names of the units and the relationships between them are generally the same in both systems, but the sizes of the units differ, sometimes considerably. Customary Units of Weights and Measures Units of Weight The pound (lb) is the basic unit of weight (which is proportional to mass). Within the English units of measurement there are three different systems of weights. In the avoirdupois system, the most widely used of the three, the pound is divided into 16 ounces (oz) and the ounce into 16 drams. The ton, used to measure large masses, is equal to 2,000 lb (short ton) or 2,240 lb (long ton). In Great Britain the stone, equal to 14 lb, is also used. The troy system (named for Troyes, France, where it is said to have originated) is used only for precious metals. The troy pound is divided into 12 ounces and the troy ounce into 20 pennyweights or 480 grains; the troy pound is thus 5,760 grains. The grain is also a unit in the avoirdupois system, 1 avoirdupois pound being 7,000 grains, so that the troy pound is 5,760/7,000 of an avoirdupois pound. Apothecaries' weights are based on troy weights; in addition to the pound, ounce, and grain, which are equal to the troy units of the same name, other units are the dram (1/8 oz) and the scruple (1/24 oz or 1/3 dram). Units of Length and Area The basic unit of length is the yard (yd); fractions of the yard are the inch (1/36 yd) and the foot (1/3 yd), and commonly used multiples are the rod (5 1/2 yd), the furlong (220 yd), and the mile (1,760 yd). The acre, equal to 4,840 square yards or 160 square rods, is used for measuring land area. Units of Liquid Measure For liquid measure, or liquid capacity, the basic unit is the gallon, which is divided into 4 quarts, 8 pints, or 32 gills. The U.S. gallon, or wine gallon, is 231 cubic inches (cu in.); the British imperial gallon is the volume of 10 lb of pure water at 62°F and is equal to 277.42 cu in. The British units of liquid capacity are thus about 20% larger than the corresponding American units. The U.S. fluid ounce is 1/16 of a U.S. pint; the British unit of the same name is 1/20 of an imperial pint and is thus slightly smaller than the U.S. fluid ounce. Units of Dry Measure For dry measure, or dry capacity, the basic unit is the bushel, which is divided into 4 pecks, 32 dry quarts, or 64 dry pints. The U.S. bushel, or Winchester bushel, is 2,150.42 cu in. and is about 3% smaller than the British imperial bushel of 2,219.36 cu in., with a similar difference existing between U.S. and British subdivisions. The barrel is a unit for measuring the capacity of larger quantities and has various legal definitions depending on the quantity being measured, the most common value being 105 dry quarts. Differences between American and British Systems Many American units of weights and measures are based on units in use in Great Britain before 1824, when the British Imperial System was established. Since the Mendenhall Order of 1893, the U.S. yard and pound and all other units derived from them have been defined in terms of the metric units of length and mass, the meter and the kilogram ; thus, there is no longer any direct relationship between American units and British units of the same name. In 1959 an international agreement was reached among English-speaking nations to use the same metric equivalents for the yard and pound for purposes of science and technology; these values are 1 yd=0.9144 meter (m) and 1 lb=0.45359237 kilogram (kg). In the United States, the older definition of the yard as 3,600/3,937 m is still used for surveying, the corresponding foot (1,200/3,937 m) being known as the survey foot. The English units of measurement have many drawbacks: the complexity of converting from one unit to another, the differences between American and British units, the use of the same name for different units (e.g., ounce for both weight and liquid capacity, quart and pint for both liquid and dry capacity), and the existence of three different systems of weights (avoirdupois, troy, and apothecaries'). Because of these disadvantages and because of the wide use of the much simpler metric system in most other parts of the world, there have been proposals to do away with the U.S. Customary System and replace it with the metric system. Bibliography See L. J. Chisholm, Units of Weights and Measure: International and U.S. Customary (U.S. National Bureau of Standards, 1967).


From Yahoo Answers

Question:The metric system is the official method of measurements in the US - it is simpler to use. Just take note: a mile is 5,280 feet???? A kilometer is 1000 meters, 1 meter= 100 centimeters and so on; Freezing point is 0 C and not a funny 32 F. Is it hard to change?

Answers:Consider the immense expense in just changing it overnight. Actually, the US is in ongoing transition, though it may take decades to finish. The traffic signs that measure distance in miles, for instance, are not going to be discarded in a jiffy. That would cost millions. However when a new is placed or a old substituted, the distance is given in kilometers. NASA recently ordered all its offices and contractors to use exclusively the metric system, 'cause of a screw up with a deep space probe. Data produced in one system was transferred and used in another. In scientific and technological fields, however, many units only indirectly related to international standards, are used, either by convenience or habit. Popular use in the US in some cases, will not change. Football is played in yards, and it is highly unlikely that fields and stadiums will be redimensioned to read in meters.

Question:

Answers:Metric is based on powers of ten; English is based on historical usage of ancient origin.

Question:This is a homework question I have so I was just wondering.

Answers:I do believe that the English (from England) use the metric system. You probably already know this but the standard metric system is the also known as the SI or international system of measurement. The units include the meter or metre, kilo, and kelvin. Most times celsius is used instead of kelvin for temperature in daily lives. On the other hand, the English system of measurement that you're refering to is used today mainly by Americans only. That includes inches, feet, miles, etc. One major difference is that the metric system only has one unit of measurement for say distance. Prefixes are added to the base unit to get kilometer or centimeter. While the English system has multiple units based on familar objects and body parts like one foot or gallon the old word for pail. Besides the people who use them, and the orgins of the units of measurement, I'm not exactly sure what a third difference would be. I think you should try working on your homework on your own anyway. Search online for websites like the ones i have listed. It shouldn't take you a long time.

Question:

Answers:1) The metric system is based on powers of 10 so it is much easier to convert units, often just by moving the decimal point. 2) Once you remember the meaning of the prefixes, you can easily convert mass, volume and distance measurements. No further conversion factors need to be memorized except the specific power of 10. But for the English System you have to remember 5280 ft = 1 mile, 4 quarts = 1 gallon, 3 feet = 1 yard, 16 oz. = 1 lb, etc. 3) The metric system is a international standard used by nearly all the countries of the world. There are actually only *three* countries (i.e. United States, Liberia and Burma) that are still using the English system.

From Youtube

Metric & Standard Measurement Systems :NASA Connect Segment explaining the development of the US standard system of measurement and the metric system and how the two systems differ.

Video Measurement Systems :Now advanced features like scanning and best fitting can be done quickly without taking up the time of skilled operators. CNC programming is a simple teach and repeat process. Just measure the part once and a full CNC program is created automatically.