**International
System of Units **
**Background Information **
"The
creation of the decimal Metric System at the time of the French Revolution and
the subsequent deposition of two platinum standards representing the meter and
the kilogram, on 22 June 1799, in the Archives de la République in Paris can be
seen as the first step in the development of the present International System
of Units.. read on... **Definitions:**
A**
quantity** in the **general sense** is a property ascribed to phenomena,
bodies, or substances that can be quantified for, or assigned to, a particular
phenomenon, body, or substance. Examples are mass and electric charge. A
**quantity** in the **particular sense** is a quantifiable or assignable
property ascribed to a particular phenomenon, body, or substance. Examples are
the mass of the moon and the electric charge of the proton. A **physical
quantity** is a quantity that can be used in the mathematical equations of science
and technology. 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. All physical quantities can be
expressed in terms of seven base units. **Derived
Units**
Other quantities, called derived quantities, are defined
in terms of the seven base quantities via a system of quantity equations. The
SI derived units for these derived quantities are obtained from these equations
and the seven SI base units. Examples of such SI derived units are given in Table
2, where it should be noted that the symbol 1 for quantities of dimension 1 such
as mass fraction is generally omitted.
**Derived Quantity** | **Name** | **Expression
in terms of SI units** | area | square
meter | m^{2} | volume | cubic
meter | m^{3} | speed,
velocity | meter per second | m/s |
acceleration | meter per second squared | m/s^{2} |
mass density | kilogram per cubic meter | kg/m^{3} |
force | netwon (N) | m·kg·s^{-2} |
pressure | pascal | m^{-1}·kg·s^{-2} |
energy, work | joule (J) N-m | m^{2}·kg·s^{-2} |
electric potential | volt (V) | m^{2}·kg·s^{-3}·A^{-1} |
More derived
units. |