Chapter 1 Measurement Measurement We measure things such

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Chapter 1 Measurement

Chapter 1 Measurement

Measurement • We measure things (such as weight, time, length, speed, etc. ) •

Measurement • We measure things (such as weight, time, length, speed, etc. ) • We use tools (rulers, clocks, speedometers, etc. ) to measure things • Measurement tools are calibrated • Calibration is in units (inches, seconds, pounds, mph’s, etc. ) • Units require standards (conventional, habitual, customary)

Modern standards • Not all quantities in nature are independent (e. g. , speed

Modern standards • Not all quantities in nature are independent (e. g. , speed is distance per time) • Standards are created for independent (base) quantities: length, time, mass, + some other • Modern day standards should be as invariable as possible • Should be uniformly defined • Should be accessible

SI (Systéme Internacional) – most accepted international system of units • Adopted in 1971

SI (Systéme Internacional) – most accepted international system of units • Adopted in 1971 • Is commonly known as metric system • Standard units are (there are more): 1 m (meter) for length 1 s (second) for time 1 kg (kilogram) for mass • All other SI units are defined as derivatives of the base units (e. g. , energy: 1 J (Joule) = 1 kg x 1 m 2 / s 2)

Length • SI unit – m (meter) • Initially adopted as one ten-millionth of

Length • SI unit – m (meter) • Initially adopted as one ten-millionth of a distance between the North pole and the equator (standard – platinum-iridium bar) • Currently - a modern standard: 1 m = the length of the path traveled by light in vacuum during a time interval of 1/299 792 458 of a second

Time • SI unit – s (second) • Historically 1 s = 1 /

Time • SI unit – s (second) • Historically 1 s = 1 / 8640 day • Currently - a modern standard: 1 s = 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 Cs 133 atom

Time • SI unit – s (second) • Historically 1 s = 1 /

Time • SI unit – s (second) • Historically 1 s = 1 / 8640 day • Currently - a modern standard: 1 s = 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 Cs 133 atom

Mass • SI unit – kg (kilogram) • Historically 1 kg – mass of

Mass • SI unit – kg (kilogram) • Historically 1 kg – mass of 1 liter of water • Initially adopted in prototype of the kilogram was made of platinum-iridium and declared: “This prototype shall henceforth be considered to be the unit of mass” • Currently - an alternative modern standard: 1 kg = mass of C 12 atom * 1026 / 1. 99264824 (Don’t confuse mass and weight: 1 kg is the same on the Earth and on the Moon)

Scientific notation 237 000 s = = 2. 37 x 108 s = =

Scientific notation 237 000 s = = 2. 37 x 108 s = = 2. 37 E 8 s 0. 0000664 m = = 6. 64 x 10 -5 m = = 6. 64 E-5 m

SI system prefixes Factor Name Symbol 1024 yotta Y 10 -1 deci d 1021

SI system prefixes Factor Name Symbol 1024 yotta Y 10 -1 deci d 1021 zetta Z 10 -2 centi c 1018 exa E 10 -3 milli m 1015 peta P 10 -6 micro µ 1012 tera T 10 -9 nano n 109 giga G 10 -12 pico p 106 mega M 10 -15 femto f 103 kilo k 10 -18 atto a 102 hecto h 10 -21 zepto z 101 deka da 10 -24 yocto y Examples: 1. 25 E 4 J = 12. 5 k. J 2. 34 x 10 -10 s = 0. 234 ns

Good SI web resource: National Institute of Standards and Technology (NIST) http: //physics. nist.

Good SI web resource: National Institute of Standards and Technology (NIST) http: //physics. nist. gov/cuu/Units/

Conversion of units • Need to know a conversion factor • Use chain-link conversion

Conversion of units • Need to know a conversion factor • Use chain-link conversion (Check Appendix D for SI conversion factors)