PHYSICS
LESSON NOTES
SSS ONE
Week one
INTRODUCTION:
Physics
is the branch of science concerned with the nature and properties of matter and
energy. It is the study of natural phenomena at its most fundamental level.
Physics deals with matter and energy and the relationship between them.
Summarily,
we can define physics as the scientific study of matter and energy and how they
interact with each other. Some of its branches are heat, sound, mechanics,
electricity, magnetism, optics(also known as light) and atomic physics.
Fundamental
quantities and Derived quantities
Physical
quantities are divided into two namely fundamental and derived quantities.
Fundamental
quantities are the basic quantities that are independent of others and cannot
be defined in terms of other quantities. The three most important of them are
the length, mass and time.
Fundamental units are units of
fundamental quantities upon which other units depend. Examples of fundamental
quantities and their units are tabulated below:
Quantity
|
Unit
|
Quantity
|
Unit
|
Length
|
Metre
(m)
|
Temperature
|
Kelvin
(K)
|
Time
|
Second
(s)
|
Current
|
Ampere
(A)
|
Mass
|
Kilogram
(kg)
|
Amount of substance
|
Mole
(M)
|
The units above are in the S.I units (Systemé Internationale
d unit). They are the principal system of units used in scientific work today.
DERIVED quantities and units are
the ones obtained by simple combination of fundamental quantities and units.
They are dependent on fundamental quantities. Examples are shown below:
Quantity
|
Unit
|
Quantity
|
Unit
|
Area
|
Square metre(m2)
|
Energy or Work
|
Joule (J)
|
Volume
|
Cubic metre (m3)
|
Power
|
Watts
|
Density
|
Kgm-3
or kg/m3
|
Momentum
|
Kgms-1
or kgm/s
|
Velocity
|
ms-1
or m/s
|
Pressure
|
Nm-2
or N/m2
|
Acceleration
|
ms-2
or m/s2
|
frequency
|
Hz or s-1
|
Force
|
N
|
MEASUREMENT AND MEASURING INSTRUMENTS
The type of instrument used for
measuring a particular quantity is determined by the quantity under
consideration.
TIME:
Measurement of time is done in the laboratory by the use of stop watch (or stop
clock). The S.I unit of time is the second. Other instruments used to measure
time are the hour-glass(or sand-glass) clock, water clock, electric clock,
pendulum clock. The most accurate clocks of all are the quartz crystal clock
and the atomic clock.
MASS: The mass of a body is the quantity
of matter contained in that body. It is measured with a balance, which are of
various types namely: beam balance (or chemical balance), lever balance, direct
reading balance. The S.I unit of mass is the kilogram (kg).
WEIGHT: The weight of a body is the
resultant force the body exerts on its support. Weight could also be defined as
the pull of the earth on the body, i.e the force with which the body is
attracted towards the centre of the earth.
The
weight of a body varies according to its distance from the centre of the earth.
An object of mass 1kg on earth has an approximate weight of 9.8N. In the
laboratory, weight is measured with a spring balance calliberated in grams
before converted to S.I unit. The S.I unit of weight is the newton (N)
VOLUME: The volume of a liquid can be
measured with measuring cylinders, flasks, pipette and burette. The measuring
flasks and pipette are used for fixed or pre-determined volume.
The volume of a regular object is obtained
by measuring its dimensions and apply the appropriate formula, while that of an
irregular object is determined by displacement method whereby the solid is
completely immersed in a cylinder containing a liquid which does not dissolve
the solid. The volume of the liquid displaced is volume of the solid object.
Assignment
1a.
Define Physics.
b. List
any FIVE branches of Physics.
2a.
Explain what is meant by fundamental quantities?
b. Mention FIVE
examples of fundamental quantities and state their units.
3. List any TEN
examples of derived quantities with their units.
4a.Differentiate
between mass and weight.
b. Describe briefly how you can determine the
volume of a piece of stone.
WEEK TWO
Measurement of Length: The dimensions
of objects can be taken by the use of metre rule, a pair of callipers,
micro-metre screw gauge.
Large distances such as the length of a
field are measured using tape rule graduated in metres. Shorter distances like
the length of a table can be obtained with a metre rule graduated in centimetres and millimetres. A
metre rule can only read to the nearest 0.1cm(i.e
1 decimal place). This is its reading accuracy.
To
avoid the error of parallax, reading is done by looking vertically downward on
the markings.
Use
of vernier callipers: A vernier calliper can be used to measure
smaller length such as the diameter of a rod, internal diameter of a cup,
thickness of a plate. It can measure to an accuracy of 0.01cm( i.e 2 decimal places). It consists of two scales: the main
scale and the vernier scale. The vernier scale enables us to measure to a
fraction of the smallest division.
Micro-metre
screw gauge:
This is used for accurate measurement of the diameter of wires or thin rods.
The instrument measures to an accuracy of 0.001cm(i.e 3 decimal places).It also has a main scale graduated in
millimetres and a circular vernier scale containing 50 divisions which is 0.5mm
of the main scale.
Dimensions
of Physical Quantities
A physical quantity is said to be in
dimensional form if it is expressed in terms of
the three fundamental quantities length (L), mass (M), and time (T). For
example, the dimension of density (with unit kgm-3) is give as ML-3.
Some other examples are as tabulated below:
Quantity
|
Derivation
|
Unit
|
Dimension
|
Velocity
|
distance/time
|
m/s or ms-1
|
LT-1
|
Acceleration
|
velocity/time
|
m/s2 or ms-2
|
LT-2
|
Density
|
mass/volume
|
kgm-3
|
ML-3
|
Force
|
mass x
acceleration
|
(N) kgm/s2
kg ms-2
|
MLT-2
|
Pressure
|
force/area
(mass x acceleration/area)
|
Nm-2
or kgm-1s-2
|
ML-1S-2
|
Momentum
|
mass x velocity
|
kgms-1
|
MLT-1
|
Power
|
work/time
(force x distance/time
|
Nms-1
orkgm2s-3
|
ML2S-3
|
We
can use the method of dimension to verify whether a physical equation is
correct or not. For example consider the
equation S = ut + ½ at2,
Dimension
of distance S (unit m) = L
Dimension of ut (m/s x s = m) = L
Dimension
of at2 (m/s2 x s2 =m) =L
Therefore, the equation S = ut + 1/2at2 is
dimensionally correct
ASSIGNMENT
1.
Which is the best instrument to measure the
thickness of a sheet of paper?
2.
When do we say a quantity is in dimensional
form?
3.
Name any TWO
instruments used to measure time in the laboratory.
4.
Write the dimensions of the following
quantities
(i) weight
(ii) pressure (iii)
acceleration (iv) power
5.
Show that the equation V2 = u2 + 2as is
dimensionally correct.
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