Measurement
MEASUREMENT
A. The
quantity and unit
a. Definition
of measure
Student
activities
1.
Measure
the length and width of the table using a ruler?
2.
Measure
the length and width of the table using your hand span?
3.
Measure
the length and width of the table using hand span of your friend?
4.
Draw
conclusions from the activities you are doing!
Measurement is to compare the activities of a physical quantity with
the similar quantity used as a unit.
b. Definition of Quantity and units
Quantity is something that can be measured, expressed in numbers
(values), and has units.
Unit is the amount of comparison that is used in the
measurement.
Example:
The length of the table using a ruler = 105.8 cm
The length of the table using a ruler = 105.8 cm
The length of the table = something that can be measured
105.8 = number / value
cm = unit
c. Base quantity
Base quantity Is a quantity that the unit has been set in
advance or not derived from other quantities. There are seven basic quantities,
there are: the length, mass, time, electrical currents, temperature, amount of
substance, and light intensity.
Basic quantity and its units according to the
International System of Units or an international system of units (abbreviated
SI) can be seen in the following table.
No.
|
Base quantity
|
Units
|
Abbreviations
|
1.
|
Length
|
Meter
|
m
|
2.
|
Mass
|
Kilogram
|
kg
|
3.
|
Time
|
Sekon
|
s
|
4.
|
Temperature
|
Kelvin
|
K
|
5.
|
Electric Currents
|
Ampere
|
A
|
6.
|
Light intensity
|
Candela
|
Cd
|
7.
|
Amount of substance
|
Mole
|
Mol
|
d. Derived Quantity
Derived quantity is a quantity that derived from the base
quantity.
Examples of some derived Quantity:
Examples of some derived Quantity:
No.
|
Derived Quantity
|
Units
|
|
MKS
|
CGS
|
||
1.
|
Area
|
m2
|
cm2
|
2.
|
Volume
|
m3
|
cm3
|
3.
|
Velocity
|
m/s
|
cm/s
|
4.
|
Acceleration
|
m/s2
|
cm/s2
|
5.
|
Force
|
Newton (N)
|
Dyne
|
Based on the value and direction, the magnitude scale is
divided into two vector and scalar quantities.
·
Scalar
quantity is a quantity that only has value and unit only. Example: volume,
area, length, mass.
·
Vector
quantity is a quantity that has a value, units and has a direction.
Example: speed, acceleration and force.
Example: speed, acceleration and force.
B. Unit System
a.
Internasional
units
The
international system is internationally accepted unit that serves as the
standard units. The international system unit requirements are:
1.
Has
a fixed value, constant in every position
2.
Is
international, can be used in every State
3.
Easily
imitated
b. MKS
and CGS Units
Ø MKS (meter, kilogram, second)
Length:
unit meter (m)
Mass:
units kilogram (kg)
Second:
second unit (s)
Ø CGS (centimeter, gram, second)
Length: unit centimeters (cm)
Mass: unit gram (g)
Second: second unit (s)
Length: unit centimeters (cm)
Mass: unit gram (g)
Second: second unit (s)
Examples Converse MKS and CGS systems
1 cm = 0.3937 inches
1 meter = 3.281 ft (feet)
1 meter = 1.094 yards
1 ft (foot) = 12 inches
1 yard = 3 ft
1 cm = 0.3937 inches
1 meter = 3.281 ft (feet)
1 meter = 1.094 yards
1 ft (foot) = 12 inches
1 yard = 3 ft
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