QUANTITIES AND UNITS
Physics quantity is something that is measurable, generally has its own unit, and it is stated in numbers or value.
For examples:
The
measurement result of the length of a table is 100 cm.
100
represent the value and cm represents the unit and the measuring
instrument of
the length is roll meter.
Fundamental Quantity
What is
base quantity?
Base Quantity (BQ) or Fundamental Quantity is the quantity whose unit has been previously
determined and it is not derived from another quantity.
Table 1.1. : Seven Fundamental Quantities
No.
|
Base Quantities
|
Symbol Quantities
|
International Units
|
Measuring Instruments
|
1.
|
Length (height, distance, displacement, width,
diameter)
|
l
|
meter (m)
|
Ruler, roll meter, vernier caliper, micrometer
caliper
|
2.
|
Mass
|
m
|
kilogram (kg)
|
Balance
scale
|
3.
|
Time
|
t
|
second (s)
|
Stopwatch
|
4.
|
Temperature
|
T
|
Kelvin (K)
|
Thermometer
|
5.
|
Electric current
|
i
|
Ampere (A)
|
Amperemeter
|
6.
|
Luminous
intensity
|
I
|
Candela (Cd)
|
Photometer
|
7.
|
Amount of substance
|
n
|
mole (mol)
|
TDS meter
|
Derived Quantity
What is
derived quantity?
Derived Quantity (DQ) is
a quantity whose unit is derived from a base quantity. Most of derived quantities have the units as a combination of base units.
Table 1.2. : Several
examples of the derived quantities
No.
|
Derived Quantities
|
International Units
|
Derived from
|
1.
|
Area (A)
|
Square meter
(m2)
|
A = length x width (BQ)
= meter x
meter = m2 (units BQ)
|
2.
|
Volume
(V)
|
Cubic meter (m3)
|
V
= length x width x height (BQ)
=
meter x meter x meter = m3 (units BQ)
|
3.
|
Speed (v), Velocity (v)
|
Meter per
second (m/s)
|
(BQ)
= ………….
(BQ)
v = ………………………
|
4.
|
Acceleration
(a)
|
m/s2
|
(DQ and BQ)
a = ………………………….
|
5.
|
Density (r)
|
Mass per
square meter (kg/m3)
|
(BQ and DQ)
= ……………………
|
6.
|
Weight
(w), Force (F)
|
Newton (N)
|
F
= mass x acceleration (BQ and DQ)
F
= …………………….
1
N = …………….
|
7.
|
Work (W), Energy (E)
|
Joule (J)
|
W = Force x displacement (DQ and BQ)
= …………….
= …………..
1 joule = ……….. = ……………..
|
8.
|
Power
(P)
|
Watt (W)
|
(DQ and BQ)
P
= …………………….
1
Watt = ……………..
|
9.
|
Pressure (P)
|
Pascal (Pa)
|
(DQ and DQ)
P = ……………………
1 Pa = ………………
|
10.
|
Momentum
(P)
|
N.s
|
P
= mass x changes velocity (BQ and DQ)
P
= ……………………….
|
What is difference between the scalar and vector quantity ?
the displacement from Sheila’s house to school is 10 kilometer
to Northwest.
Scalar Quantity is a quantity which only has a magnitude. For
examples: distance, length, time,
mass, temperature, area, volume, speed,
density, energy, etc.
Whereas, a quantity that is specified by
both a magnitude and a direction is a Vector Quantity. For examples: displacement, velocity, acceleration, force, weight, etc.
Complete
material can be downloaded here
Exercise
on Chapter Quantities and Unit
