Measurement in everyday life
Measurement of mass
Measurement of volume
Measurement in everyday life
Measurement of length
Measurement of temperature
Need for measurement in
physics
 To understand any phenomenon in physics we have to
perform experiments.
 Experiments require measurements, and we measure several
physical properties like length, mass, time,
pressure etc.
temperature,
 Experimental verification of laws & theories also needs
measurement of physical properties.
Physical Quantity
 A physical property that can be measured and described by a
number is called physical quantity.
Examples:
•
Mass of a person is 65 kg.
•
Length of a table is 3 m.
•
Area of a hall is 100 m2.
•
Temperature of a room is 300 K
Types of Physical Quantities
1. Fundamental quantities:
 The physical quantities which do not depend on any other physical
quantities for their measurements are known as fundamental
quantities.
Examples:
• Mass
• Length
•
•
Time
Temperature
Types of Physical Quantities
2. Derived quantities:
 The physical quantities which depend on one or more fundamental
quantities for their measurements are
known as derived
quantities.
Examples:
•
•
Area
Volume
•
•
Speed
Force
Units for measurement
 The standard used for the measurement of a physical
quantity is called a unit.
Examples:
•
metre, foot, inch for length
•
kilogram, pound for mass
•
second, minute, hour for time
•
fahrenheit, kelvin for temperature
Characteristics of units
Well – defined
Suitable size
Reproducible
Invariable
Indestructible
Internationally acceptable
CGS system of units

This system was first introduced in France.

It is also known as Gaussian system of units.

It is based on centimeter, gram and second
as the fundamental units of length, mass
and time.
MKS system of units

This system was also introduced in France.

It is also known as French system of units.

It is based on meter, kilogram and second as
the fundamental units of length, mass and
time.
FPS system of units

This system was introduced in Britain.

It is also known as British system of units.

It is based on foot, pound and second as the
fundamental units of length, mass and time.
International System of units (SI)
 In
1971, General Conference on Weight and Measures
held its meeting and decided a system of units for
international usage.
 This
system is called international system of units and
abbreviated as SI from its French name.
 The
SI unit consists of seven fundamental units and
two supplementary units.
Seven fundamental units
Definition of metre
The metre is the length of the path
travelled by light in a vacuum during a
time interval of 1/29,97,92,458 of a
second.
Definition of kilogram
The kilogram is the mass of prototype
cylinder of platinum-iridium alloy
preserved at the International Bureau
of Weights and Measures, at Sevres,
near Paris.
Prototype cylinder of platinum-iridium alloy
Definition of second
One second is the time taken by
9,19,26,31,770 oscillations of the
light emitted by a cesium–133 atom.
Two supplementary units
1. Radian: It is used to measure plane angle
θ = 1 radian
Two supplementary units
2. Steradian: It is used to measure
solid angle
Ω = 1 steradian
Rules for writing SI units
1
Full name of unit always starts with small letter even if named
after a person.
•
newton
•
ampere
•
coulomb
not
•
Newton
•
Ampere
•
Coulomb
Rules for writing SI units
2
Symbol for unit named after a scientist should be in capital
letter.
•
N for newton
•
A for ampere
•
K for kelvin
•
C for coulomb
Rules for writing SI units
3
Symbols for all other units are written in small letters.
• m for meter
• kg for kilogram
• s for second
• cd for candela
Rules for writing SI units
4
One space is left between the last digit of numeral
and the symbol of a unit.
• 10 kg
• 5N
• 15 m
not
• 10kg
• 5N
• 15m
Rules for writing SI units
5
The units do not have plural forms.
•
6 metre
•
14 kg
•
20 second
•
18 kelvin
not
•
6 metres
•
14 kgs
•
20 seconds
•
18 kelvins
Rules for writing SI units
6
Full stop should not be used after the units.
•
7 metre
•
12 N
•
25 kg
not
•
7 metre.
•
12 N.
•
25 kg.
Rules for writing SI units
7
No space is used between the symbols for units.
•
4 Js
•
19 Nm
•
25 VA
not
•
4Js
•
19 N m.
•
25 V A.
SI prefixes
Factor Name Symbol Factor Name Symbo
l
1024
1021
yotta
zetta
exa
peta
tera
giga
Y
Z
E
P
T
G
106
103
mega
M
kilo
k
102
101
hecto
h
deka
da
1018
1015
1012
109
10−1
10−2
deci
centi
milli
micro
nano
pico
d
c
m
μ
n
p
10−15
10−18
femto
f
atto
a
10−21
10−24
zepto
z
yocto
y
10−3
10−6
10−9
10−12
Use of SI prefixes
•
3 milliampere = 3 mA = 3 x 10−3 A
•
5 microvolt = 5 μV = 5 x 10−6 V
•
8 nanosecond = 8 ns = 8 x 10−9 s
•
6 picometre = 6 pm = 6 x 10−12 m
•
5 kilometre = 5 km = 5 x 103 m
•
7 megawatt = 7 MW = 7 x 106 W
Some practical units for measuring length
1 micron = 10−6 m
Bacterias
1 nanometer = 10−9 m
Molecules
Some practical units for measuring length
1 angstrom = 10−10 m
Atoms
1 fermi = 10−15 m
Nucleus
Some practical units for measuring length


Astronomical unit = It is defined as the mean
distance of the earth from the sun.
1 astronomical unit = 1.5 x 1011 m
Distance of planets
Some practical units for measuring length


Light year = It is the distance travelled by light in
vacuum in one year.
1 light year = 9.5 x 1015 m
Distance of stars
Some practical units for measuring area
•
Acre = It is used to measure large areas in British
system of units.
1 acre = 208’ 8.5” x 208’ 8.5” = 4046.8 m2
•
Hectare = It is used to measure large areas in French
system of units.
1 hectare = 100 m x 100 m = 10000 m2
•
Barn = It is used to measure very small areas, such as
nuclear cross sections.
1 barn = 10−28 m2
Some practical units for measuring mass
1 metric ton = 1000 kg
Steel bars
1 quintal = 100 kg
Grains
Some practical units for measuring mass
1 pound = 0.454 kg
1 slug = 14.59 kg
Newborn babies
Crops
Some practical units for measuring mass
•
1 Chandrasekhar limit = 1.4 x mass of sun = 2.785 x 1030 kg
•
It is the biggest practical unit for measuring mass.
Massive black holes
Some practical units for measuring mass
•
1 atomic mass unit =
1
12
x mass of single C atom
•
1 atomic mass unit = 1.66 x 10−27 kg
•
It is the smallest practical unit for measuring mass.
•
It
is
used
to
single atoms, proton and
measure
neutron.
mass
of
Some practical units for measuring time
•
1 Solar day = 24 h
•
1 Sidereal day = 23 h & 56 min
•
1 Solar year = 365 solar day = 366 sidereal day
•
1 Lunar month = 27.3 Solar day
•
1 shake = 10−8 s
Seven dimensions of the world
Fundamental Quantities
Dimensions
Length
L
Mass
M
Time
T
Temperature
K
Current
A
Amount of substance
N
Luminous intensity
J
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