1-2 Measuring things:
The board (1 of 2)
Physical Quantities
Examples: Length
Pressure Power
Speed (velocity) Mass Temperature
Acceleration Time Electric current
Base
Quantities
Derived
Quantities
are
independent of
each other
are defined in
terms of the
base quantities
Examples
Mass
Speed =
Length
Time
1-2 Measuring things:
Units :
Examples:
Board 2 of 2
Each physical quantity is
measured in terms of its own
units.
Quantity (symbol)
Unit (symbol)
Length (L)
Meter (m)
Mass (m)
Kilogram (kg)
Velocity (V)
Meter per second (m/s)
Standards :
Each base quantity is measured by comparison
with a standard.
The base standard corresponds to 1 unit of the
base quantity.
Standards have to be both:
accessible and invariable .
1-3 The International System of Units
The board
(1 of 2)
The SI system is also called : the metric system.
The 7 SI base units:
Unit
name
meter
Second
Kilogram
Ampere
Unit
symbol
m
s
kg
A
Kelvin
Mole
K
mol
Candela
cd
‫ عليكم فقط‬:‫من هذا الجدول‬
‫المكتوب باألحمر‬
Quantity
Quantity
name
Symbol
Length
L
Time
t
Mass
m
Electric
I
current
Temperature
Amount of
N
substance
Luminous
J
intensity
Example of an SI derived unit:
Unit
name
Watt
Unit
symbol
W
In terms of the
base units
kg.(m^2)/(s^3)
Quantity
name
Power
1-3 The International System of Units The board
(2 of 2 )
Scientific Notation:
560 000 000 m = 5.60 × 108 m
0.000 000 492 s = 4.92 × 10−7 s
Prefixes of SI units:
Factor
109
106
103
10−2
10−3
10−6
10−9
10−12
Prefix
GigaMegaKiloCentiMilliMicroNanoPico-
‫كل الذي في الجدول‬
‫داخل في االختبار‬
Symbol
G
M
K
C
M
µ
n
p
A prefix in an example:
1.27 × 109 watt = 1.27 gigawatts = 1.27 GW
1-4 Changing units
Covered in the
introductory
lecture
a conversion factor is a ratio of units that is equal to unity.
Examples:
1 – 5, 1 – 6, 1 – 7 : Length, Time, and Mass :
Clocks Inventions (the time measuring devices) through history:
‫ لن تدخل في االختبار‬،‫ هذه الصفحة خارج المنهج‬The board (1 of 2)
1st (Oldest)
2nd
3rd
4th
5th
(current)
‫بديع الزمان الجزري‬
Al-Jazari
1 – 5, 1 – 6, 1 – 7 : Length, Time, and Mass :
The board
(2 of 2)
one ten-millionth of
the distance from the
North Pole to the
equator.
Later
In 1792
Historical definitions of the meter (the standard for Length):
the distance between
two fine lines engraved
near the ends of a
platinum-iridium bar.
‫التعريفين التاريخيين لن يدخلوا في االختبار‬
Nowadays, the standard used for each quantity is as follows:
Length
Time
Mass
The meter:
The Second: The kilogram:
the distance
travelled by
light during a
precisely
specified
time interval.
the
oscillations
of light
emitted by
an atomic
(cesium133) source.
a platinum-iridium
standard mass kept near
Paris
The atomic mass unit:
the mass of a single
carbon-12 atom.
1 u = 1.66 x 10-27 kg
Density The mass per unit volume =