Créer une présentation
Télécharger la présentation

Télécharger la présentation
## Metric System

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**Metric System**Mr. Holstrom Biology …**We are Scientists, We use the Metric System!**• Length • Mass • Time • Temperature • First, a little historical information on the system • Then, a review of the prefixes • Finally, specifics for:**History of the Metric System**• Created at the end of the 18th Century to provide a consistent system of units amidst a wide variety of different standards. • Previously, each area had its own units inherited from earlier times. • Not reproducable, not standard • e.g., a "cubit" was the length from the elbow to the tip of the middle finger. • e.g., a rundlet was worth 16 gallons in a certain town and 18 gallons in another town**History, Part 2**• The metric system became compulsory in France on Dec.10, 1799 (Napoleon was First Consul) and, being practical, spread slowly across Europe. • Not without resistance : a few years later, even France came back to the old system for several years. • Japan made it official in 1868 and Russia in 1917. • England was the last European country to adopt it : the adaptation period began in 1965 and was to end officially in 1980.**History, Part 3**• In 1960, the SI (International System) was created • It fine tuned the system, introducing some new units and shedding others. • It replaces the old systems, named MKSA, MTS, and CGS (although some intrepid physicists still use CGS from time to time, which is considered OK since they do at least provide a consistent set of secondary units.)**History, Part 4**• The seven primary units are now : • * length : meter (m) • * mass : kilogram (kg) • * time : second (s) • * electric current : ampere (A) • * temperature : Kelvin or Celsius (K or °C) • * quantity of matter : mole • * light intensity : candela (cd)**King Henry Died By Drinking Chocolate MilkKilo, Hecta, Deca,**Base, Deci, Centi, Milli Easy Way to Remember your Prefixes:**Prefixes**One of the clever ideas behind the system was to use only multiples of ten. Today mainly multiples of 1000 are in use. These are the only words to memorize (if you're not lucky enough to have enjoyed them since Grade 3) : * 1018 : exa- (E) * 1015 : peta- (P) * 1012 : tera- (T) * 109 : giga- (G) * 106 : mega- (M) * 103 : kilo- (k) * 10-3 : milli- (m) * 10-6 : micro- (µ) * 10-9 : nano- (n) * 10-12 : pico- (p) * 10-15 : femto- (f) * 10-18 : atto- (a)**Old, but not Forgotten**Some prefixes by ten, around the main unit, are still in use : * 100 : hecto- (h) like in hectolitre (used by the breweries) * 10 : deca- (da) like in decameter (sometimes written dekameter) * 0.1 : deci- (d) like in decibel * 0.01 : centi- (c) like in centiliter (same root as "cent", you may say centidollar !)**Length**Unit of length: meter The meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second.**Old Anglo Saxon Units**Used today ONLY in USA • inch : 25.4 mm • foot = 12 inches = 0.3048 m • yard = 3 feet = 0.9144 m • mile = 1760 yards = 1609.344 m (derived from the Roman Mile : "mille passus" equal to 1000 paces or double steps, estimated at 1475 to 1522 m. This makes the step = 0.75 m (remember the Romans were not as tall as we are). • nautical mile = 6076.115 feet = 1852 m**USA and the Metric System**• Thomas Jefferson considered a conversion to the metric system. In 1889, the US Congress adopted the meter as a standard and, thereafter, the inch, foot, yard, etc. were defined in relation to the meter. • The Metric Conversion Act of 1975 committed the US to the increasing use of, and voluntary conversion to, the metric system of measurement.**Mass**Unit of mass: kilogram The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.**Kilogram**• As the name implies, the original unit was the gram (weight of 1 cubic centimeter or 1 milliliter of water at 4 °C) but it soon became the kg (or 1000 grams or one cubic decimeter of water), and defined by its model in platinum-iridium kept in Paris. • One may also mention the carat used in jewelry (5 carats = 1 gram). But carat is not an SI unit!**Old Anglo-Saxon Units**• pound : 0.45359237 kg in the Avoirdupois system (but 0.3732417 kg in the Troy and Apothecaries systems.) The smallest unit common to the different systems is the grain ( = 64.7989 milligrams) with 7000 grains making one (Avoirdupois) lb. and 5760 grains for one pound in the other systems. The abbreviation "lb" comes from the equivalent Roman weight "libra”. • ounce : In Avoirdupois : 437.5 grains ( = 28.3495 g -- 16 oz = 1 lb.). In the other systems : 480 grains ( = 31.10348 g -- 12 oz = 1 lb.) 12 Roman "unciae" made 1 "libra" - uncia simply means one twelfth in Latin.)**Time**Unit of time: second The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.**Nature Gives Us Natural Time Scales**• Originally, the second was 1/86400 of the mean solar day. • But, the mean solar day changes slowly, so it was redefined on a steadier atomic level • Original Cesium clocks good to about 1 second every 3,000 years**Temperature**Unit of thermodynamic temperature: Kelvin The Kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.**History of Temperature Scales**The first to seal mercury in a glass rod was Daniel Fahrenheit in Germany (1709). He had to build a scale from scrap : zero was allocated to the temperature of a salty mixture, assuming that nothing could ever be colder and 96 was his estimate of the human body. With such a scale, water would freeze at 32 and boil at 212. 1686 - 1736**History of Temperature Scales**• In 1730, in France, Rene Antoine Ferchault de Reaumur built the first alcohol thermometer. He allocated 0 to freezing water and 80 to boiling water. • In 1742, in Sweden, the astronomer Anders Celsius used a scale allocating 100 to freezing water and 0 (!) to boiling water. His scale was later inverted (0 to freezing water and 100 for boiling) and long known as "centigrade". Celsius 1701 - 1744**Half a Dozen One, 6 to the Other**• Comparing the scales, 9° Fahrenheit = 4° Reaumur = 5° Celsius * C = (F - 32) * 5/9 * F = 32 + C * 9/5 • The two scales meet at - 40 * - 40°F is the same as - 40°C**Absolute Temperature**• Starting from the absolute zero (at -273.15 C or -459.67 F), it was tempting to follow the old idea of Fahrenheit and have only a positive scale. This was done by Sir William Thomson, Lord Kelvin, from the Celsius scale. • Water is freezing at 273.15 K, and boiling at 373.15 K • The SI uses the Kelvin scale, defined by the triple point of water (at 273.16 K or 0.01°C) and absolute zero. 1824 - 1907**Significant Digits**The digits in a measured or calculated quantity are those digits which are known with certainty Rules: 1. When adding or subtracting measured quantities, the precision of the answer can only be as great as the least precise term in the sum or difference. All digits up to this limit of precision are significant. 2. When multiplying or dividing measured quantities, the number of significant digits can be only as great as the least number of significant digits in any factor in the calculation.**Insights into Sig Figs**Zeroes can be confusing. They often appear only to locate the decimal point…which means they are not significant. Using scientific notation will resolve this issue. Calculators cannot increase the number of sig figs in nor the precision of your measurements. You must round off the result to the correct number of digits.