The SI Metric System LE SYSTÈME INTERNATIONAL D'UNITÉS ( I N T ERNATI ONA L SYST E M O F U N I T S)

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1 The SI Metric System LE SYSTÈME INTERNATIONAL D'UNITÉS (INTERNATIONAL SYSTEM OF UNITS)

2 Metric System Created standard system of measurement Decimal system (base of 10) Uses decimal-based prefixes to denote multiples & sub-multiples of base units General Conference on Weights and Measures (CGPM) est Image source: boomeria.org/chemlectures

3 History France (1790s) Length & Mass meter, kilogram Germany (1830s) Time second Britain (1900) Electrical ampere CGPM (1954) Temperature & Luminance Kelvin, candela CGPM (1971) Quantity of matter - mole Image source: mined from Google images

4 CGPM Meetings 1st (1889) The International Prototype Kilogram (IPK), a cylinder made of platinum-iridium and the International Prototype Metre, an X-cross-section bar also made from platinum-iridium were selected from batches manufactured by the British firm Johnson Matthey. Working copies of both artifacts were also selected by lot and other copies distributed to member nations, again by lot. The prototypes and working copies were deposited at the International Bureau of Weights and Measures (Bureau international des poids et mesures), Sèvres, France. 2nd (1897) No resolutions were passed by the 2nd CGPM. 3rd (1901) The litre was redefined as volume of 1 kg of water. Clarified that kilograms are units of mass, "standard weight" defined, standard acceleration of gravity defined endorsing use of grams force and making them well-defined. 4th (1907) The carat was defined as 200 mg. 5th (1913) The International Temperature Scale was proposed.

5 CGPM Meetings 6th (1921) The Metre Convention revised. 7th (1927) The Consultative Committee for Electricity (CCE) created. 8th (1933) The need for absolute electrical unit identified. 9th (1948) The ampere, bar, coulomb, farad, henry, joule, newton, ohm, volt, watt, weber were defined. The degree Celsius was selected from three names in use as the name of the unit of temperature. The symbol l (lowercase L) was adopted as symbol for litre. Both the comma and dot on a line are accepted as decimal marker symbols. Symbols for the stere and second changed. The universal return to the Long Scale numbering system was proposed but not adopted.

6 CGPM Meetings 10th (1954) The kelvin, standard atmosphere defined. Work on the International System of Units (metre, kilogram, second, ampere, kelvin, candela) began. 11th (1960) The metre was redefined in terms of wavelengths of light. The Units hertz, lumen, lux, tesla were adopted. The new MKSA-based metric system given the official symbol SI for Système International d'unités and launched as the "modernized metric system". The prefixes pico-, nano-, micro-, mega-, giga- and tera- were confirmed. 12th (1964) The original definition of litre = 1 dm 3 restored. The prefixes atto- and femto- were adopted. 13th (1967) The second was redefined as duration of periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom at a temperature of 0 K. The Degree Kelvin renamed kelvin and the candela redefined. 14th (1971) A new SI base unit, the mole defined. The names pascal and siemens as units of pressure and electrical conductance were approved.

7 CGPM Meetings 15th (1975) The prefixes peta- and exa- were adopted. The units gray and becquerel were adopted as radiological units within SI. 16th (1979) The candela and sievert were defined. Both l and L provisionally allowed as symbols for litre. 17th (1983) The metre was redefined in terms of the speed of light. 18th (1987) Conventional values were adopted for Josephson constant, KJ, and von Klitzing constant, RK, preparing the way for alternative definitions of the ampere and kilogram. 19th New prefixes yocto-, zepto-, zetta- and yotta- were adopted.

8 CGPM Meetings 20th (1995) The SI supplementary units (radian and steradian) become derived units. 21st (1999) A new SI derived unit, the katal = mole per second, was adopted as the SI unit of catalytic activity. 22nd (2003) A comma or a dot on a line are reaffirmed as decimal marker symbols, and not as grouping symbols in order to facilitate reading; "numbers may be divided in groups of three in order to facilitate reading; neither dots nor commas are ever inserted in the spaces between groups". [11] 23rd (2007) The definition of the kelvin was clarified and thoughts about possible revision of certain base units discussed. 24th Proposal to revise the definitions of the SI units, including redefining the kilogram in relation to the Planck constant were accepted in principle, subject to certain technical criteria having been met.

9 CGPM Meetings 25th (2014) Redefining the kilogram in relation to the Planck constant was discussed but not decided on. Progress towards realising the redefinition has been noted. However, it was concluded that the data did not yet appear to be sufficiently robust. Continued effort on improving the data has been encouraged, such that a resolution that would replace the current definition with the revised definition can be adopted at the 26th meeting.

10 International System (SI) Published by CGPM in 1960 Adopted as a standard system of measurement throughout the world in 1960s Continues to evolve regular meetings every 4 to 6 years Most recent proposal change the definition of the kilogram base unit

11 Anti-Metric System Hold outs U.S.A. Liberia Myanmar (formerly Burma)

12 Seven Base Units Meter Kilogram Second Kelvin Mole Ampere Candela Let s look at the origins for each measurement in your lab manual (p. 27?)

13 Current Definitions of Base Units Meter (m) - The distance travelled by light in vacuum in 1/ second. Kilogram (kg) - There is a standard platinum/iridium 1 kg mass housed near Paris at the International Bureau of Weights and Measures (BIPM). Second (s) - the duration of periods of the radiation corresponding to the transition between the two hyperfine levels of the cesium-133 atomic ground state. Kelvin (K) - the fraction 1/ of the thermodynamic temperature of the triple point of water.

14 Current Definitions of Base Units Ampere (A) - that constant current which, if maintained in two infinitely long straight parallel conductors which have negligible circular crosssection, and placed 1 m apart in vacuum, would produce between a force between the conductors equal to 2 x 10-7 newton per meter of length. Mole (mol) - the amount of a substance which contains as many entities as there are atoms in kilograms of carbon-12. Candela (cd) - luminous intensity, in a given direction, of a source emitting monochromatic radiation of frequency 540 x 1012 hertz with radiant intensity in that direction of 1/683 watt per steradian.

15 System of Prefixes

16 Using Prefixes - Meter 1 micrometer (µm) = meter 1 millimeter (mm) = meter 1 centimeter (cm) = 0.01 meter 1 decimeter (dm) = 0.1 meter 1 dekameter (dkm) = 10 meters 1 hectometer (hm) = 100 meters 1 kilometer (km) = 1000 meters

17 Conversion Factors

18 Recording Measurements THE SCIENTIFIC WAY

19 Precision vs Accuracy Precision Reproducibility Check by repeated measurements Poor precision results from poor techniques Accuracy Correctness Check by using a different method Poor accuracy results from procedural or equipment flaws

20 Precision vs Accuracy

21 Significant Figures SIG-FIGS Image source: schooltutoring.com

22 Sig-Figs Merriam-Webster: Significant (adj.): having meaning Significant figures of a number are those digits that carry meaning contributing to the number s accuracy, and thus the reliability of the data being collected.

23 Sig-Figs The precision of an instrument reflects the number of significant figures in a reading Micro-balance versus bathroom scale The number of significant figures in a lab measurement is the number of digits that are known accurately, plus one that is uncertain or doubtful. Image source: chemsite.lsrhs.net/measurement

24 Rules of Sig-Figs

25 Rules of Sig-Figs

26 Sig-Figs: Cardinal Rule of Calculation A final result or calculation should never contain any more significant figures than the least precise data used to calculate it. Measurement #1 = cm Measurement #2 = 1.62 cm Calculator: = cm 2 Report: 48.8 cm 2

27 Sig-Figs: General Rule of Calculation The concept applies only to measured quantities. For example, numbers that are standard (known) quantities are assumed to have an infinite number of sig-figs. There are 100 centimeters in a meter : etc. centimeters etc. meters

28 Sig-Figs: Adding & Subtracting Use least number of decimal places: Calculator: = Sig-fig Rule: = (one decimal place) Calculator: = Sig-fig Rule: = (two decimal places)

29 Sig-Figs: Multiplying & Dividing Use least number of sig-figs: Calculator: = Sig-fig Rule: = 49 (two sig-figs) Calculator: = Sig-fig Rule: = 34.1 (three sig-figs)

30 Rounding If a calculation yields a result that would suggest more precision than the measurement from which it originated, rounding off to the proper number of significant figures is required.

31 Scientific Notation BASE 10 SYSTEM Image source: boundless.com/physics

32 Scientific Notation Must be written in the following format: Only one number in the one s place Significant Figures Base 10 Positive or negative exponent

33 Move the decimal Image Source: algebra-class.com