Definition of A Physical Quantity
Formally, the International Vocabulary of Metrology, 3rd edition (VIM3) defines quantity as:
Property of a phenomenon, body, or substance, where the property has a magnitude that can be expressed as a number and a reference.Hence the value of a physical quantity q is expressed as the product of a numerical value Nq and a unit of measurement uq;
Quantity calculus describes how to perform mathematical manipulations of quantities.
Examples
- If the temperature T of a body is quantified as 300 kelvin (in which T is the quantity symbol, 300 the value, and K is the unit), this is written
- T = 300 × K = 300 K,
- If a person weighs 120 pounds, then "120" is the numerical value and "pound" is the unit. This physical quantity mass would be written as "120 lb", or
- m = 120 lb
- If a person traveling with a yardstick, measures the length of such yardstick, the physical quantity of length would be written as
- L = 36 inches
- An example employing SI units and scientific notation for the number, might be a measurement of power written as
- P = 42.3 × 103 W,
In practice, note that different observers may get different values of a quantity depending on the frame of reference; in turn the coordinate system and metric. Physical properties such as length, mass or time, by themselves, are not physically invariant. However, the laws of physics which include these properties are invariant.
Read more about this topic: Physical Quantity
Famous quotes containing the words definition of a, definition of, definition, physical and/or quantity:
“Definition of a classic: a book everyone is assumed to have read and often thinks they have.”
—Alan Bennett (b. 1934)
“It’s a rare parent who can see his or her child clearly and objectively. At a school board meeting I attended . . . the only definition of a gifted child on which everyone in the audience could agree was “mine.””
—Jane Adams (20th century)
“Perhaps the best definition of progress would be the continuing efforts of men and women to narrow the gap between the convenience of the powers that be and the unwritten charter.”
—Nadine Gordimer (b. 1923)
“I have no purpose to introduce political and social equality between the white and black races. There is a physical difference between the two, which, in my judgement, will probably for ever forbid their living together upon the footing of perfect equality; and inasmuch as it becomes a necessity that there must be a difference, I ... am in favour of the race to which I belong having the superior position.”
—Abraham Lincoln (1809–1865)
“The Great Society is a place where every child can find knowledge to enrich his mind and to enlarge his talents.... It is a place where the city of man serves not only the needs of the body and the demands of commerce but the desire for beauty and the hunger for community.... It is a place where men are more concerned with the quality of their goals than the quantity of their goods.”
—Lyndon Baines Johnson (1908–1973)