SI Base Units Agreed upon standard units of

SI Base Units -Agreed upon standard units of measure

Base Unit Definitions • Kilogram (kg) -- the base unit of mass in the SI version of the metric system. The kilogram was originally defined to be the mass of one cubic decimeter of pure water. • The kilogram is now defined as the mass of the standard kilogram, a platinum -iridium cylinder in the custody of the International Bureau of Weights and Measures (BIPM) near Paris, France. Base • Meter (m) -- the metric and SI base unit of distance. Originally, the meter was designed to be one ten-millionth of a quadrant, the distance between the Equator and the North Pole. • The 17 th General Conference on Weights and Measures in 1983 defined the meter as that distance that makes the speed of light in a vacuum equal to exactly 299 792 458 meters per second.

Base Unit Definitions • Kelvin (K) -- The SI base unit of temperature, previously called the degree Kelvin (°K). In 1967 the General Conference on Weights and Measures defined the temperature of the triple point of water (the temperature at which water exists simultaneously in the gaseous, liquid, and solid states) to be exactly 273. 16 kelvins. • One kelvin represents the same temperature difference as one degree Celsius. • The original Celsius scale was established as 100 equal divisions between the triple point of water and the boiling point of water.

Base Unit Definitions • Mole (mol) -- The SI base unit of the amount of a substance (as distinct from its mass or weight). • Moles measure the actual number of atoms or molecules in an object. • The official definition, adopted as part of the SI system in 1971, is that one mole of a substance contains just as many elementary entities (atoms, molecules, ions, or other kinds of particles) as there atoms in 12 grams of carbon-12. • 1 m of any substance contains the same number of “elementary particles. ” • Avogadro's number = 6. 02 x 1023

Base Unit Definitions • Second (s) -- Fundamental unit of time in all measuring systems and the SI base unit of time, first defined as 1/86, 400 mean solar day. • Now defined as the period of time it takes for to 9, 192, 631, 770 cycle of radiation to be emitted by atoms of cesium-133.

Base Unit Definitions • Ampere (A) -- The SI base unit of electric current, named for the French physicist André-Marie Ampère (1775 -1836). • The constant current that will produce an attractive force of 2 × 10 − 7 newtons per meter of length between two straight, parallel conductors…. . • Detailed definition is beyond the scope of this course. • Candela (cd) -- The SI base unit for measuring the intensity of light. Candela is the Latin word for "candle. " The unit has a long and complicated history, originally, representing the intensity of an actual candle. • Detailed definition is beyond the scope of this course.

• The SI system uses standards of measurement, called base units. • Other units used in the SI system that are not base units are derived from the base units.

SI Derived Units of Measure – examples

• The SI system is based on multiples of ten. • Factors of ten are represented by prefixes. • You either multiply or divide by a factor of ten to convert from one SI unit to another.

SI Prefixes

Units of Measurement Prefix Abbreviation Name Notation Giga- G Billion 1, 000, 000 Mega- M Million 1, 000 Kilo- K Thousand 1, 000 Hecto- H Hundred 100 Deca- D Ten 10 BASE UNIT -none- deci- d Tenth 0. 1 centi- c Hundredths 0. 01 milli m Thousandths 0. 001 micro- µ Millionth 0. 000001 nano n Billionth 0. 00001