2. Measurement
It is the art of comparing unknown values to a
standard, or the accepted set of values for a
particular quantity.
Physical variables such as time, temperature and
length can be used to quantitatively describe
physical phenomena.
The standards in which the physical quantities
are expressed are called units.
3. Measurement
In the past until the first half of 1900s, the
organization was known as the metric system.
Then in 1960, the organization was called Systeme
International d’Unites or the International
System of Units. The new name was adopted by
the 11th General Conference on Weights and
Measures. There are seven Fundamental quantities
and units in the SI, which are best remembered by
the acronym METTALL.
4. Physical Quantity Unit Definition
M Mass Kilogram (kg) A kilogram is defined by an International
prototype kilogram made of platinum-iridium
and is kept in the International Bureau of
Weights and Measures in Sevres, France.
E Electric
Current
Ampere (A) An ampere is the current maintained in two
straight wires, placed one meter apart in
vacuum which produce a force of 2 × 10−7
Newton per meter of Length.
T Time Second (sec) A second is associated with the specified
transition of Cesium-133 atom, during which 9
192 631 770 cycles of microwaves radiation
are generated by the atom.
5. T Temperature Kelvin (K) The Kelvin scale is named after physicist
William Thompson (popularly known as
Lord Kelvin) and is similar in intervals in
the Celsius scale. Adding 263.15 to the
Celsius temperature reading will equal to
the measure in Kelvin.
A Amount of
Substance
Mole (mol) The mole is the amount of substance
contained in 0.012 kg of Carbon-12. One mole
of substance contains 6.02 × 1023 particles of
atoms.
L Length Meter (m) A meter is defined as the distance traveled by
light in vacuum in
1
299 792 458
second.
L Luminous
Intensity
Candela
(cd)
A candela is the intensity of light produced by
a source emitting with a frequency of
540 × 1012 cycle/second in a direction where
the intensity is
1
683
Watt per steradian.
6. Some quantities can be taken from the
combination of other quantities. Theses are called
derived quantities. Examples of such are area, volume,
acceleration, force and pressure. Observe how these
quantities are derived.
Area = l w = 𝑚2
Volume = (l)(w)(h) = 𝑚3
Acceleration = ratio between distance and the square of
time =
𝑚
𝑠2
Force = product of mass and acceleration = (kg)
𝑚
𝑠2 =
Newton (N)
Pressure = ratio between force and area =
𝑁
𝑚2
7. Quantity Unit Conversion
Area
1 square kilometer (𝑘𝑚2
) 1 000 000 𝑚2
1 hectare (ha) 10 000 𝑚2
1 acre
Volume
1 cubic meter (𝑚3) 1 𝑚3
1 cubic centimeter (𝑐𝑚3
) 0.000001 𝑚3
1 kiloliter (kL) 1 000 L
1 centiliter (cL) 0.01 L
Mass and Weight 1 metric ton (t) 1 000 000 g = 1 000 kg
1 centigram (cg) 0.01 g
Force, Energy,
Frequency,
Pressure and
Power
1 Newton (N) 1 kg •
𝑚
𝑠2
1 Joule (J) 1 𝑚2
•
𝑘𝑔
𝑠2
1 Hertz 1
𝑠
1 Pascal 𝑘𝑔
𝑚 − 𝑠2
1 Watt 1 𝑚2
•
𝑘𝑔
𝑠3
