Definitions and symbols for units

Appendix 3. Definitions and Symbols for Units reproduced with permission from Mills I et al. (1993) Quantities, Units and Symbols in Physical Chemistry, 2nd edn., Oxford Blackwell Science. 

The recognised body in the United Kingdom for the preparation of specifications for quality, performance or dimensions, methods of test, definitions and symbols, codes of practice, etc. British Standards are prepared under the guidance of representative committees and are widely circulated before they are authorised for publication. BSI co-operates in preparing international standards for rubber and plastics through ISO/TC45 and ISO/TC61 respectively. See ISO. 

The tables are arranged by subject. The five columns in each table give the name of the quantity, the recommended symbol(s), a brief definition, the symbol for the coherent SI unit (without multiple or submultiple prefixes, see p.74), and footnote references. When two or more symbols are recommended, commas are used to separate symbols that are equally acceptable, and symbols of second choice are put in parentheses. A semicolon is used to separate symbols of slightly different quantities. The definitions are given primarily for identification purposes and are not necessarily complete they should be regarded as useful relations rather than formal definitions. For dimensionless quantities a 1 is entered in the SI unit column. Further information is added in footnotes, and in text inserts between the tables, as appropriate. 

The lUPAC recommendation Manual of Symbols and Terminology for Physicochemical Quantities and Units Appendix II Definitions Terminology and Symbols in Colloid and Surface Chemistry, Part 1.13 Selected Definitions, Terminology and Symbols for Rheological Properties, Pure Appl. Chem. 51 (1979) 1213 also contains recommendations for surface rheology. Only part of them are heeded in this chapter. 

The notation and nomenclature employed arc those recommended in the IUPAC Manual of Symbols and Terminology for Physico-chemical Quantities and Units, Appendix II, Part 1.13 (Selected Definitions, Terminology and Symbols for Rheological Properties). Pure and Applied Chemistry, 1979, 51, 1213-8. Alternatives to D and a are respectively y and T. 

Physiccjl qucj ntity Ncjme of unit Symbol for unit Definition and value of unit in SI... 

Quantity Symbol and definition Dimensions SI unit Symbol for unit... 

SI, definitions and symbols, 1-23 to 26 Units for Magnetic Properties, 1-27 Upper Critical (UCST) and Lower Critical... 

The elastic and viscoelastic properties of materials are less familiar in chemistry than many other physical properties hence it is necessary to spend a fair amount of time describing the experiments and the observed response of the polymer. There are a large number of possible modes of deformation that might be considered We shall consider only elongation and shear. For each of these we consider the stress associated with a unit strain and the strain associated with a unit stress the former is called the modulus, the latter the compliance. Experiments can be time independent (equilibrium), time dependent (transient), or periodic (dynamic). Just to define and describe these basic combinations takes us into a fair amount of detail and affords some possibilities for confusion. Pay close attention to the definitions of terms and symbols. 

See nomenclature for definition of symbols and units. The units presented are English engineering units, unless a conversion is required. The friction factor is the only experimental variable that must be determined by reference to the above equations and it is represented by Figure 2-3. Note that this may sometimes be referred to as the Fanning formula, and may be modified to )held a fric-... 

For historic reasons a number of different units of measurement have evolved to express quantity of the same thing. In the 1960s, many international scientific bodies recommended the standardisation of names and symbols and the adoption universally of a coherent set of units—the SI units (Systeme Internationale d Unites)— based on the definition of five basic units metre (m) kilogram (kg) second (s) ampere (A) mole (mol) and candela (cd). 

More details and definition of other units may be found in the Manual of Symbols and Terminology for Physicochemical Quantities and Units, Whiffen, 1979, Pergamon Press. 

A substantial number of definitions in the terminology section are either of physical quantities or are expressed mathematically. In such cases, there are recommended symbols for the quantities and, when appropriate, corresponding SI units. Other terms have eommon abbreviations. The following format is used to indicate these essential eharaeteristics name of term (abbreviation), symbol, SI unit unit. Typical examples are tensile stress, interpenetrating polymer network (IPN). If there are any, alternative names or synonyms follow on the next line, and the definition on the sueeeeding lines. 

SI units should be used throughout the report. The symbols for SI units are not abbreviations and do not require definition in the report. These symbols are defined in the official SI brochure (3). 

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