Measurement

MEASUREMENT

What is measurement?
Measurement refers to the comparison of an unknown quantity with a standard.
= it judge against a quantity with a standard to see
how many times as big as the standard the quantity is.

Background of Measurement

Unit of the quantity = standard for describing magnitudes of physical quantities.

1791 =metric system of measurement was established, Paris Academy of Sciences

o Meter was originally define as one ten-millionth of the distance from the equator to the North pole

o Second as the time for a pendulum one meter long to swing from one side to the other.

1889 the definitions of the basic units have been established by an international organization, the general Conference on weights and Measures.

1960 it has been known officially as the International System or SI (the abbriviation for the French equivalent, Syteme International)

o meter was define by an atomic standard, in terms of the wavelength of the orange- red light emitted by atoms of Krypton (86Kr) in a glow discharge tube; one meter was define as 1650763.73 of these wavelength.

o the unit of time was based on a certain fraction of the mean solar day, the average time interval between successive arrivals of the sun at its highest point in the sky.

1967 is an atomic one, based on the two lowest energy states of the cesium atom.

o One second = the time required for 9192631770 cycles of this radiation

November 1983 the standard was change again in a more radical way.

o Meter is the distance light travels in 1/299792458 second.

The common Physical Quantity

Length is a physical quantity for measuring space. The distance between two points.

Mass is a basic property of matter. The mass of an object is measure of the amount of matter it contains. The mass of an onject does not vary with the location. It remains the same even if the position of the object is changed with reference to the earth’s center.

Density is a quantity derived from mass and volume.

Time is the interval between two successive events.




PREFIX
Abbriviation
Power of ten
Atto
a
10-18
Femto
f
10-15
Pico
p
10-12
Nano
n
10-9
Micro
m
10-6
Milli
m
10-3
Centi
c
10-2
Deci
d
10-1
Deca
D
101
Hecto
H
102
Kilo
K
103
Mega
M
106
Giga
G
109
Tera
T
1012
Peta
P
1015
Exa
E
1018