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)
“Beauty, like all other qualities presented to human experience, is relative; and the definition of it becomes unmeaning and useless in proportion to its abstractness. To define beauty not in the most abstract, but in the most concrete terms possible, not to find a universal formula for it, but the formula which expresses most adequately this or that special manifestation of it, is the aim of the true student of aesthetics.”
—Walter Pater (1839–1894)
“Scientific method is the way to truth, but it affords, even in
principle, no unique definition of truth. Any so-called pragmatic
definition of truth is doomed to failure equally.”
—Willard Van Orman Quine (b. 1908)
“There are two kinds of timidity—timidity of mind, and timidity of the nerves; physical timidity, and moral timidity. Each is independent of the other. The body may be frightened and quake while the mind remains calm and bold, and vice versë. This is the key to many eccentricities of conduct. When both kinds meet in the same man he will be good for nothing all his life.”
—Honoré De Balzac (1799–1850)
“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)