# 9.2.2: Basic Units Blocks

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In Thermo–Fluid science there are several basic physical quantities which summarized in Table 9.1. In the table contains two additional physical/basic units that appear in magnetohydrodynamics (not commonly use in fluid mechanics). Many (almost all) of the engineering dimensions used in fluid mechanics can be defined in terms of the four basic physical dimensions MM, LL ,tt and θθ. The actual basic units used can be S.I. such as kilograms, meters, seconds and Kelvins/Celsius or English system or any other system. In using basic new basic physical units, MM, LL, tt, and θθ or the old system relieves the discussion from using particular system measurements. The density, for example, units are Mass/Length3Mass/Length3 and in the new system the density will be expressed as M/L3M/L3 while in S.I. kg/m3kg/m3 and English system it slug/ft3slug/ft3. A common unit used in Fluid Mechanics is the Force, which expressed in SI as Newton [NN]. The Newton defined as a force which causes a certain acceleration of a specific mass. Thus, in the new system the force it will be defined as MLt−2MLt−2. There are many parameters that contains force which is the source reason why the old (or alternative) system use the force instead the mass. There many physical units which are dimensionless by their original definition. are the angle, strains, ratio of specific heats, kk, friction coefficient, ffand ratio of lengths. The angle represented by a ratio of two sides of a triangle and therefore has no units nor dimensions. Strain is a ratio of the change of length by the length thus has no units. Quantities used in engineering can be reduced to six basic dimensions which are presented in Table 9.1. The last two are not commonly used in fluid mechanics and temperature is only used sometimes. Many common quantities are presented in the following Table 9.3.

Table 9.3 Physical units for two common systems. Note the second (time) in large size units appear as "ss'' while in small units as "secsec."

 Standard System Old System Name Letter Units Name Letter Units Area L2L2 [m2m2] Area L2L2 [m2m2] Volume L3L3 [m3m3] Volume L3L3 [m3m3] Angular Velocity 1t1t [m3m3] Angular Velocity L3L3 [m3m3] Acceleration Lt2Lt2 [msec2][msec2] Acceleration Lt2Lt2 [msec2][msec2] Angular Acceleration 1t21t2 [1sec2][1sec2] Angular Acceleration 1t21t2 [1sec2][1sec2] Force MLt2MLt2 [kgmsec2][kgmsec2] Force Ft2LFt2L [Ns2m][Ns2m] Density ML3ML3 [kgL2][kgL2] Density Ft2L4Ft2L4 [Ns2m4][Ns2m4] Momentum MLtMLt [kgmsec][kgmsec] Momentum FtFt [Nsec][Nsec] Angular Momentum ML2tML2t [kgm2sec][kgm2sec] Angular Momentum LFtLFt [mNsec][mNsec] Torque ML2t2ML2t2 [kgm2s2][kgm2s2] Torque LFLF [mN][mN] Absolute Velocity MM1t2MM1t2 [kgms][kgms] Absolute Velocity tFL2tFL2 [Nssec][Nssec] Kinematic Viscocity L2tL2t [m2s][m2s] Kinematic Viscocity L2tL2t [m2s][m2s] Volume Flow Rate L3tL3t [m3sec][m3sec] Volume Flow Rate L3tL3t [m3sec][m3sec] Mass Flow Rate MtMt [kgsec][kgsec] Mass Flow Rate FtLFtL [Nsm][Nsm] Pressure MLt2MLt2 [kgms2][kgms2] Pressure FL2FL2 [Nm2][Nm2] Surface Tension Mt2Mt2 [kgs2][kgs2] Surface Tension FLFL [Nm][Nm] Work or Energy ML2t2ML2t2 [kgm2s2][kgm2s2] Work or Energy FLFL [Nm][Nm] Power ML2t3ML2t3 [kgm2s3][kgm2s3] Power FLtFLt [Nmsec][Nmsec] Thermal Conductivity MLt3θMLt3θ [kgms3K][kgms3K] Thermal Conductivity FLtFLt [NsK][NsK] Specific Heat L2t2θL2t2θ [m2s2K][m2s2K] Specific Heat L2Tt2L2Tt2 [m2s2K][m2s2K] Entropy ML2t2θML2t2θ [kgm2s2K][kgm2s2K] Entropy LFTLFT [mNK][mNK] Specific Entropy L2t2θL2t2θ [m2s2K][m2s2K] Specific Entropy L2t2TL2t2T [m2s2K][m2s2K] Molar Specific Entropy ML2t2MθML2t2Mθ [m2s2Kmol][m2s2Kmol] Molar Specific Entropy FL2TMFL2TM [NmKmol][NmKmol] Enthalpy ML2t2ML2t2 [kgm2s2][kgm2s2] Enthalpy LFLF [mN][mN] Specific Enthalpy L2t2L2t2 [m2s2][m2s2] Specific Enthalpy L2t2L2t2 [m2sec2][m2sec2] Thermo Dynamic Force MLt2MMLt2M [kgms2mol][kgms2mol] Thermo Dynamic Force NMNM [Nmol][Nmol] Catalytic Activity MtMt [molsec][molsec] Catalytic Activity MtMt [molsec][molsec] Heat Transfer Rate ML2t3ML2t3 [kgm2sec3][kgm2sec3] Heat Transfer Rate LFtLFt [mNsec][mNsec]

This page titled 9.2.2: Basic Units Blocks is shared under a GNU Free Documentation License 1.3 license and was authored, remixed, and/or curated by via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

This page titled 9.2.2: Basic Units Blocks is shared under a GNU Free Documentation License 1.3 license and was authored, remixed, and/or curated by Genick Bar-Meir via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.