1.2 Dimensions and Units Physical quantities characterized by dimensions The seven fundamental(or primary) Primary dimensions dimensions and their units in SI Dimension Unit Length meter (m) Mass kilogram(kg) Time second (s) Secondary dimensions? Temperature kelvin (K) Electric current ampere(A) Amount of light candela(cd) Force,Energy,velocity,volume,... Amount of matter mole (mol) Two important unit systems: weight of a unit mass ·SI (Metric) kg(or mole),m,sec,K kg at sea evel ·English (USCS) Ib,ft/inch,sec,F 8=9.807m/s2 1Ib=0.45359237kg1ft=0.3048m IN 1Pa W=9.807kgm/s2 1in=25.4mm 1 kg.m/s2 1N/m2 =9.807N 1gal=3.785L Unit conversion ratio 1 kgf 上游充通大学 February 28,2019 12 SHANGHAI JLAO TONG UNIVERSITYFebruary 28, 2019 12 1.2 Dimensions and Units Physical quantities characterized by dimensions Primary dimensions ? Secondary dimensions? Two important unit systems: • SI (Metric)  • English (USCS) Force, Energy, velocity, volume,… kg(or mole), m, sec, K lb, ft/inch, sec, ºF 1 lb = 0.45359237 kg 1 ft = 0.3048 m 1 in = 25.4 mm 1 gal = 3.785 L weight of a unit mass at sea evel Unit conversion ratio 2 1 Pa 1 N / m