Basic dimensions and units

The convention followed in this book is that aU physical quantities are in italic type, while symbols for units are in normal type, so for instance we might say that the force F is 15 N the viscosity rj is 10 Pa.s and the shear rate y is 0.1 s-i=. S5rmbols for unit names derived from proper names begin with a capital letter but the tmit names themselves are not capitalised, i.e. N for newton, P for pascal and Hz for hertz. The unit name should not be followed by a full stop, and plurals of unit symbols should not be followed by an s, e.g. 3 kg but not 3 kg. or 3 kgs. If we are quoting temperature T in absolute units, i.e. kelvin, then no ° s)mibol is needed, e.g. 200 K. However if you are quoting the temperature in Celsius or similar, you should put °C. 

Inserting a raised dot properly indicates multiplication of units, but a full stop (period, US)—as used here—is usually acceptable because some people only have access to a limited character set on their keyboards. However leaving a space between the units is also acceptable, so we can happily write either Nm, N.m or N m, but not Nm Here we shall keep to the fuU-stop/period convention (as in Pa.s) which is well understood and easily typed, but when writing for particular companies or scientific journals, you should check their preferred house-style. Division is indicated by the use of a forward slash / or a negative exponent, but repeated use of a forward slash is not allowed, so for acceleration we write m/s or m.s-2 but not m/ s/ s. 

The numerical value and the unit S)nnbol should be separated by a space, even when used as an adjective in normal writing, e.g. 35 mm, not 35mm or even 35-mm A zero should always be placed in front of the decimal point for numbers less than one, e.g. 0.3 J but not. 3 J. The SI unit for volume, the litre, is best represented by L and not the lower case 1 which is easily confused with the numeral 1 in most character fonts. 

Exercise 3 Qieck out http //physics.nist.gov/Document/checklist.pdfon the Internet for the US government s official view on the rules and style conventions for SI units. Standard rheological nomenclature, as approved by the (American) Society of Rheology may be found at www.umecheme.maine.edu. 

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