Units of measurement
Out of basic four quantities, length, time,
mass and force
At least three should arbitrarily defined
and the fourth may be derived as
F = m a
This derived expression includes mass, length
and time. There are two unit systems S I and
US Customary FPS
For si unit length, time and mass are arbitrary
while force is derived
Whereas for fps system length, time and force
are arbitrary while mass is derived
Si unit for length is meter represented by
a small m, seconds for time donated by small
s and kilogram for mass written as kg
Force is derived using f=ma which give Newton
(N)
On the other hand, in U S system, basic unit
of length is foot, feet in plural. The time
has the same unit, while force is represented
by pound. (lb) which is short for libra pondo
While unit of mass, slug, is derived using
same expression.
Therefore, Gravitational acceleration constant
at sea-level and 45-degree latitude is 9.81
meter per second square in SI while 32.2 feet
per second square in FPS system.
SI is used abundantly around the world expect
in US, Canada, Libya and Burma.
SI units are used in more than 95% of the
world’s countries.
Prefix,
A prefix is used before the unit if quantity
is very large or very small to get an idea
of the magnitude and size
A prefix may represent a multiple or sub multiple
of a unit
Prefixes progress usually by three decimal
places apart
4 million newton is written as four thousand
kilonewton4 meganewton or 0.004 Giganewton
Similarly 0.005 meter is equal to 5 millimeter,
5 thousand micrometer or five million nanometer.
Tera peta exa pico fecto atto are rarely used
There are certain rule of regarding si units
First, symbols can never be in plural form,
this causes confusion with seconds, the unit
of time donated by an s
Second, units are never capitalized unless
they are multiples higher than kilo or named
after an individual, such as N for Issac Newton,
P for Blaise Pascal and C for Anders Celcius
Thirdly, exponents are over both prefix and
unit simultaneously. Square on N of microNewton
covers both the prefix micro and the unit
newton.
Fourth, all units in combination should be
in base form. Kilo Newton and nanometer to
be reduced to Newton and meter.
Fifth, compounds can never be used. Such as
kilo-micro-meter. It is simply millimetre
Sixth, the multiples of seconds are usually
minutes and hours for practical approach.
