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Unformatted text preview: ME 200: Thermodynamics I Lecture 2: Units, Specific volume, , and Pressure, p Prof. Sojka Summer 2011 In this Lecture Units Specific volume, Pressure, p 2 Dimensions and Units Physical quantities, i.e. properties, are reported in terms of their dimensions. Primary dimensions Examples: mass (kg), length (m), time (s), temperature (K), etc. Secondary dimensions Derived from primary dimensions. Examples: velocity (m/s), specific volume (kg/m 3 ), force (N), energy (J), etc. 3 Dimensions and Units We use two systems of units: SI units (Metric/SI) English Engineering units (USCS) Dimension SI Unit USCS Unit Mass kg lb m Length m ft Time s s Force N lb f Temperature K R Velocity m/s ft/s Energy J lb fft, Btu Power W lb fft/s, hp Pressure Pa lb f /in 2 (psi) 4 Units Conversions Come from Newtons 2 nd Law for a unit mass 1N = 1kgm/s 2 1 lb f = 32.174 lb mft/s 2 Important Note difference between lb f and lb m : lb f is a force unit (like N) lb m is a mass unit (like kg) 5 6...
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 Summer '08
 GAL

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