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 A4.  PHYSICAL QUANTITY - working definition 

The value of a physical quantity is defined as equal to the product of a number and a unit:

value of a physical quantity = number x unit

or replacing the name with the quantity symbol  m  and the unit name with the
SI unit symbol  kg

e.g., mass = 5.2 x kilogram

m = 5.2 kg

Similarly,  time = 10.6 x second

NOTE 1:

in S.I. quantity symbols are italicized, in sloping typeface, which distinguishes them from the same letters selected for unit symbols.

t = 10.6 s

A space is inserted between the number and its unit symbol.  Why is this ?

NOTE 2: 

Manipulations of equations involving physical quantities and units follow the laws of algebra/indices.

At the outset, it is important for one to absolutely clear about the distinction, in a given context, between the:

  • recognized SI unit symbol

e.g., s

  • name of the corresponding SI unit(s)

  • quantity symbol(s) in common use

  • name of the physical quantity being used

second

t    (N.B. these are italicized)

time

SI-Illustration-Constants.jpg
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