Chapter 1 Measurement
Chapter 1 Measurement
Despite the mathematical beauty of some of its most complex and abstract theories physics is above all an experimental science
Despite the mathematical beauty of some of its most complex and abstract theories, physics is above all an experimental science
1-1 Physical quantities, standards and units What will be measured? Physical quantities: mass, length, time, force What's the standard for a measurement? Maintaining and developing standards is an active branch of science Units There are seven kinds of base units in SI system
1-1 Physical quantities, standards and units • What will be measured? Physical quantities: mass, length, time, force… • What’s the standard for a measurement? Maintaining and developing standards is an active branch of science. • Units There are seven kinds of base units in SI system
-2 The international system of units cGPM(国际度量衡大会) selected as base units the seven quantities displayed in Table 1-1. This is the basis of the International System of Units abbreviated sl
1-2 The international system of units CGPM(国际度量衡大会) selected as base units the seven quantities displayed in Table 1-1. This is the basis of the International System of Units, abbreviated SI
Table 1-1 SI Base units Quantity Name Symbol Time Second Length Meter Mass Kilogram Kg Amount of Mole Mol substance Temperature Kelvin Electric current Ampere K—A Luminous intensity Candela cd
Table 1-1 SI Base units Quantity Name Symbol Time Second s Length Meter m Mass Kilogram Kg Amount of substance Mole Mol Temperature Kelvin K Electric current Ampere A Luminous intensity Candela cd
Am I a nine giga-angstrom(109A)waist or a ten? aw I a Mine Lhiga-angstrom 0 The use of non-SI units is particularly popular with astronomers many of whom are in love with the angstrom
The use of non-SI units is particularly popular with astronomers, many of whom are in love with the angstrom . Am I a nine giga-angstrom (109 ) waist or a ten? A
1-3 The standard of time We can use any phenomenon that repeats itself as a measure of time One second was defined to be 1/86400 of one day In 1967, the 13th CGPM adopted a new definition The second is the duration of 9. 192, 631.770 vibrations of a(specified) radiation emitted by a (specified) isotope of the cesium atom
1-3 The standard of time • We can use any phenomenon that repeats itself as a measure of time. • In 1967, the 13th CGPM adopted a new definition: • One second was defined to be 1/86400 of one day. The second is the duration of 9,192,631,770 vibrations of a (specified) radiation emitted by a (specified) isotope of the cesium atom
1-4 The standard of leng Ith The first international standard of length was a bar of a platinum-iridium alloy called the standard meter In 1960. the 1 1 th cgpm defined the meter as the length of 1, 650, 763. 73 wave length of a special radiation of Kr86 In 1983. the 17th CGPM redefined the meter as the length of the path traveled by light in vacuum during a time interval 1/299.792 458 of a second
1-4 The standard of length • The first international standard of length was a bar of a platinum-iridium alloy called the standard meter. • In 1983, the 17th CGPM redefined the meter as the length of the path traveled by light in vacuum during a time interval 1/299,792,458 of a second. • In 1960, the 11th CGPM defined the meter as the length of 1,650,763.73 wave length of a special radiation of Kr86
1-5 The standard of mass The SI standard of mass is a platinum-iridium cylinder and assigned as a mass of 1 kilogram (prototype) Secondary standards are sent to standardizing laboratories in other countries Atomic mass unit
1-5 The standard of mass • The SI standard of mass is a platinum-iridium cylinder and assigned as a mass of 1 kilogram (prototype). • Secondary standards are sent to standardizing laboratories in other countries. • Atomic mass unit
1-6 Precision and significant figures (有效数字) The number of significant figures tells us the precision of the measuring result There are a few simple rules to follow in deciding how many significant figures to keep Rule 1. X=3.0m and X=0.0030km imply that we know the value of to be two significant figures Be careful about ambiguous notations: X=300m
1-6 Precision and significant figures (有效数字) • The number of significant figures tells us the precision of the measuring result. • There are a few simple rules to follow in deciding how many significant figures to keep: Rule 1. x=3.0m and x=0.0030km imply that we know the value of x to be two significant figures. Be careful about ambiguous notations: x=300m
