# Unit-1.B_Measurement_physical-quantities-units-and-conversion.pdf

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1Unit 1.2. Physical quantities, units, and conversionTextbook Readings:TopicReferencesUnits of measurementSection 1.5 of Brown et al. 2018Contents1.2.1. Physical Quantities and Units of Measurement........................................................................................11.2.2. Unit prefixes and Scientific Notation.........................................................................................................31.2.3. Conversion of Units and Quantity Calculus...............................................................................................41.2.1. Physical Quantities and Units of MeasurementMany properties of matter arequantitative, that is, they are associated with numberswhich in turn indicateomultitude(many or few), oromagnitude (big or small.A property of this kind is known as aquantity.A quantity is specified by performing ameasurement,which is a process of assigning of anumber to a characteristic or property of an object or a phenomenon.In the process of measurement, the units of the quantity must also be specified.oTheunitof measurement is a definite multitude or magnitude of a quantity definedby law (of man and the universe) or convention.oExamples are the ones defined by theSystème International d’Unités(French name)or SI Units, which we will use generally in the course.We also often use the termphysical quantityto describe a property of matter, energy orchange that can be specified by measurement.In the SI units, there areseven base unitsfor the most fundamental physical quantities,which are used (first by physicists) to quantitatively describe everything in the universe(that is known to human beings). All other units can bederivedfrom these base units.Table 1. SI Base UnitsPhysicalquantityName ofunitSymbolDefinitionTimesecondSThe duration of 9,192,631,770 cycles of theradiation of a certain emission of thecesium atom.LengthmeterMDistance travelled by light in a vacuumduring a time interval of 1/299,792,458 s
2MasskilogramKgDefined by taking the fixed numerical valueof the Planck constant, h, to be 6.626 07015 × 1034when expressed inthe unit J-s, which is equal to kg m2s1.Theprevious definition of kg is it is the mass ofa prototype made of platinum-iridium keptat the International Bureau of Weights andMeasures in France.

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