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CHAPTER 1: Units, Physical Quantities, Dimensions 1. PHYSICS is a science of measurement. The things which are measured are called physical quantities which are defined by the describing how they are to be measured. There are three fundamental quantities in mechanics: Length Mass Time
A unit is a particular physical quantity, defined and adopted by convention, with which other particular quantities of the same kind are compared to express their value. A measurement is a direct or indirect comparison of a certain quantity with an appropriate standard or unit of measurement.
However, there is a set of limited number of physical quantities of fundamental importance from which all other possible quantities can be derived. Those fundamental quantities are called Base Physical Quantities, and obviously the other derivatives are called Derived Physical Quantities.
This is a unit-at-a-glance list. You can also download a PDF version for off-line use. Table I. Basic units Table II. Derived units with assigned names Table III a. SI Units prefixes Table III b. Binary prefixes for Bytes Table IV. Accepted non-SI units Table V. Accepted non-SI units with experimental values Table VI. Units deprecated by the SI
The International System of Units, universally abbreviated SI (from the French Le Système International d’Unités ), is the modern metric system of measurement. Long the dominant measurement
Derived units are formed for convenience of notation and are mainly used by various branches of science. They are obtained by combining base units and other derived units algebraically.
unit of length is the meter, its unit of time is the second and its unit of mass is the kilogram. Other quantities in physics are derived from these. For example the unit of energy is the joule, defined by 1J = 1 kg·m2 s2. As a convenience in using the SI system we can associate prefixes with the basic units to represent powers of 10.
