Selasa, 07 Februari 2012

Measurement



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 = 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:
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.





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)
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



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