MEASUREMENT UNITS IN ENGINEERING AND SI

The history of the use of measuring systems is briefly reviewed, the confusion arising from the use of numerous metric systems of units is discussed, and features of the SI that eliminate such confusion are examined. SI is a single system consisting of seven base units (length, mass, time, electric current, temperature, amount of substance, and luminous intensity) and two supplementary units (plane angle and solid angle). There is only one unit for each quantity in SI. The same name is not used for units of a different nature like mass and force. All derived units are related to the base and supplementary units by the factor one; this makes SI a unitory or coherent system rather than a decimal system. Some derived units have special names but these names do not alter the maxim of one unit for each quantity. The prefixes provided for convenience in expressing multiples and submultiples of SI units, are not essential to SI. Units are derived from the base units or from those derived units having special names. In all, there are only 38 terms in SI. The use of SI eliminates vexing problems in engineering. Angle is not a dimensionless quantity in SI. The radian should be included in appropriate derived units. In order to have balanced equations, the radian must be included in units for moment of inertia, angular momentum, and torque. When this is done, the problem of the unit for energy, N.M., used also as a unit of torque, disappears. Although SI is the best current system, improvements are needed. The use of SI cannot eliminate the use of all other systems.

  • Supplemental Notes:
    • Report of a symposium conducted by Standing Subcommittee No. 5, International Activities of the U.S. National Committee on Tunneling Technology, held on May 21-22, 1974 in Washington, D.C.
  • Corporate Authors:

    National Research Council

    National Committee on Tunneling Technology
    Washington, DC  United States  20418
  • Authors:
    • Stiehler, R D
  • Publication Date: 1975

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Filing Info

  • Accession Number: 00127933
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Apr 21 1976 12:00AM