INTRODUCTION TO PHYSICS
Physics is the branch of science that deals with the study of matter in relation to energy.
Thus physics explains energy and forces. Physics is the systematic study of the way
objects, matter and energy moves, changes and interacts. It is really concerned with how
fast things move, when they move and what causes things to move. Those things can be
the very large like stars or galaxies or the very small, groups of objects or single objects.
It is also about what makes up the fundamental building blocks of the reality we live in.
IMPORTANCE OF PHYSICS
Studying the way things moves and interact in the world is fundamentally useful in all
sorts of way. In some cases it is crucial to our survival. Interestingly our own brains have
needed to develop an automatic understanding of physics, for example being able to walk
or balance requires our brains to make lots of calculations about friction and forces. It
plays a role in engineering, medical and surgical research, surveying work. Physics is
crucial to virtually all of our modern technology, conveniences and infrastructure from
computers to cameras and everyday appliances. Physics is also used in other scientific
fields like biology and chemistry. For example: The physics of biology becomes
biophysics. Physics of astronomy becomes astro physics and physics of the earth
becomes geophysics but physics is useful in everyday situations. Having an awareness of
physics can help explain:

Friction breaks and crashes.

How water boils or freezes.

How simple machines work.

Working out how fast or slow things go.

Predicting where things go and when they get there.
CLASSIFICATION OF PHYSICS
Typically physics is classified into traditional areas of study. These include:

Atomic/nuclear- the study of the very small

Mechanics/Dynamics - how things move

Electromagenetics- including light and radio waves.

Thermodynamics - heat and temperature

Quantum physics - movements of single atoms or particles

Light/sound (Acoustics)- waves
But often these areas overlap each other. In some cases all use similar principles to
describe special circumstances.
MEASUREMENT AND EXPERIMENTATION IN PHYSICS
Introduction
In no subject does measurement play as important a role as in science. Real science
cannot exist without measurement. Experiments in Physics involve the measurement of
various quantities and a great deal of effort has gone into making these measurements as
accurate and reproducible as possible. So certain basic standards of measurements have
been established and units agreed upon internationally.
Estimation
If accurate measurement is necessary it is always advisable to estimate. This would help;
you to avoid silly mistakes that frequently take place while calculating. For better
estimations, specially for large numbers, comparison is easier to make.
Approximation
In measurements approximation also plays an important role. In day to day practice we
always use approximation. You must have heard people saying "It is approximately five
minutes walk from the church."
Quantitative Versus Qualitative
Most experiments in physics require the observations made to be quantitative rather than
qualitative. If observations are only descriptive or qualitative, they are likely to be
imprecise and could cause disagreements between experimenters. For example, scientists
cannot merely say that an object is large or small. Instead they have to specify its size as
a quantity, that is, with a number and using a standard unit such as kilogram. This is
called a quantitative observation.
PHYSICAL QUANTITIES
UNITS
Unit is a standard for comparison. In earlier times the measurement of quantity of things
was quite arbitrary. In many cases it was related to the dimension of different parts of the
human body. These parts were chosen as "units" to measure these quantities. For
example, for measuring length, distance between the nose and the fingers or outstretched
hand was used as a unit.
British System
In this system the unit of length is foot (F), of mass is the pound (P) and of time is the
second (S).
METRIC SYSTEM
A system of measurement which is based upon the powers of ten. Each unit quantity was
divided into ten parts and each of these parts into further ten and so on. Multiples of the
unit are ten, one hundred, one thousand etc. This was very logical. Once the size of the
unit had been determined say, the "meter", submultiples were named decimeter,
centimeter, millimeter for one tenth, one hundredth and one thousandth of a meter
respectively. Multiples were named as the decameter (x 10), hectometer (x 100) and
kilometer (x 1000) etc.
The prefixes used in the system are shown in table below:
In the Metric System there are two commonly used systems of measurement, one based
on the Meter, Kilogram and Second (MKS) and the other on the Centimeter, Gram and
Second (CGS).
International System of Units
An International System of Units (abbreviated as SI)is based on the metric system of
measurement. It helps scientists working in different parts of the world to compare their
data (measurements) easily.
 Unit of Length is defined as the length of the path traveled by light in vacuum
during a time interval of 1/(2.99792458 X 108) seconds.
 Unit of Mass is defined as "the mass of a particular solid cylinder made of
platinum-iridium alloy kept in Paris, known as the International Prototype
Kilogram".
 Unit of time, second, is equal to the duration of 9192631770 periods of the
radiation corresponding to the transition between two hyperfine levels of the
ground state of the caesium –133 atoms.
The following table shows the basic units in the SI system together with their symbols:
Basic Units in the SI System
Usually all small measurements are expressed by using the prefixes - deci, centi, milli,
etc. with the units.
For large measurements, we use deca, hecto, kilo etc. as prefixes with the units. The
symbol and meaning of each prefix is given below
Units of all other physical quantities can be derived from the basic units and hence are
called "derived units". The following table shows the list of various physical quantities,
derived formula and corresponding SI Units:
DERIVED UNITS
ACCURACY IN MEASURING
Least Count
It is the smallest reading that can be accurately measured while using an instrument or a
device. For example the least count of various measuring devices are listed below:
SIGNIFICANT FIGURES
These express the degree of accuracy of measurements. It is a statement which gives
number of digits up to which we are sure about their accuracy. It gives the degree of
accuracy or precision made with the instrument. In practical life we depend only on
approximate measurements. We ignore small measurements when we are computing
large measurements. For example, we may measure the length of a wall as 10 meters and
57 centimeters or 10.57 meters. The actual length of the wall is between 10 meters 57.5
cm and 10 meters 56.5 cm. Now we can say that the length 10.57 meters is correct up to
four significant figures.
EXAMPLE 1
(a) 8.88 correct to two significant figures is 8.9, because 8.88 is nearer to 8.9 than to 8.8.
(b) On the other hand 8.82 correct to two significant figures is 8.8. This is because 8.82 is
nearer to 8.8 than to 8.9.
EXAMPLE 2
Correct the number 8.5775
(a) up to 2 significant figures = 8.6
(b) up to 3 significant figures = 8.58
(c) up to 4 significant figures = 8.578
EXAMPLE 3
Suppose you are measuring the diameter of a cylinder using a vernier caliper
as 2.38 cm. The accurate value may lie between 2.375 cm and 2.385 cm. In this case
figures 2 and 3 are absolutely correct while 8 is reasonably correct. This measurement is
said to be accurate up to 3 significant figures.
RULES FOR DETERMINING SIGNIFICANT DIGITS
 All the digits from 1, 2, 3, 4, …., 9 are significant digits.
 Zeros (0s) if they occur between non-zero digits, are significant.
For example, in the number- 325007, 2409, 308, zeros in between the digits are
significant.
 The final zeros (0s) of an approximated number when expressed as decimal are
significant, e.g.,
(i)
8.70 meters means approximation is to the nearest centimeters (i.e., two
decimal places).
(ii)
(ii) 5.430 kg means approximation is to the nearest gram (i.e., three decimal
places).
 0s (zeros) which are used only to locate the decimal point are non-significant e.g.,
0.007, 0.09, 0.4
Accurate Measurement
No measurement is ever perfectly accurate. Even with high precision instruments some
error is inevitable.
There are two main types of errors:
Random errors occur in all measurements. They arise when observers estimate the last
figure of the reading on an instrument. These include the noise in the room or the
mechanical vibrations in the room. These are called random, because they cannot be
predicted. The best way of minimizing the error is to take the average of many readings.
Systematic errors: Such mistakes are not random, but constant. They may cause an
experimenter to under estimate or over estimate a reading. Systematic errors may be due
to defective equipment - for instance, an incorrectly marked ruler; or they may be due to
environmental factors - for instance, the weather conditions on a particular day. While
recording time using a stop-watch, your reaction time in starting or stopping the stopwatch will certainly vary at times significantly if you are tired or distracted. At times the
variation will be more than a few hundredth of a second.
Percentage Error
While reading the length of a simple pendulum or the length of a resistance wire or while
finding the weight of a body using spring balance, mass by a beam balance etc., we are
likely to make mistakes. The percentage error can be calculated by using the formula.
Percentage error
For example, if the length of an object (100cm long) is measured as 99.8 cm, then
% error
MEASUREMENT OF LENGTH
Different types of lengths are measured by using different types of instruments. Lengths
like the length of cloth or length of a line can be measured by using measuring tape, a
metre scale or a foot rule. But these instruments cannot be used to measure the diameter
of a metal sphere or a cylinder. To measure the diameter of a cylinder we can use paper
strip method and wooden block method:
(i)
The correct way to read a ruler is shown in the figure below. The eye must be
positioned vertically above the mark to avoid error due to Parallax.
(ii)
Paper strip method: Wind a strip of paper closely round the object once and
prick the overlapping position with a pin (Shown in figure below).
A method for measuring diameter of a cylinder
Unwind the paper strip and measure the distance between the two pinholes. This
measure is the measure of the circumference, since circumference = (
x diameter).
Hence now the diameter can be calculated.
(iii)
Wooden block method: Place the sphere or the cylinder between two blocks in
contact with a ruler as shown in figure below.
A simple method for measuring diameter of a sphere
Read the distance between the two blocks on the ruler accurately. (The line of sight
should be vertical.)
Vernier Calliper
The meter scale enables us to measure the length to the nearest millimeter only.
Engineers and scientists need to measure much smaller distances accurately. For this
a special type of scale called Vernier scale is used.
The Vernier scale consists of a main scale graduated in centimeters and millimeters.
On the Vernier scale 0.9 cm is divided into ten equal parts. The least count or the
smallest reading which you can get with the instrument can be calculated as under:
Least count = one main scale (MS) division - one vernier scale (VS) division.
= 1 mm - 0.09 mm
= 0.1 mm
= 0.01 cm
The least count of the vernier
= 0.01 cm
The Vernier calliper consists of a main scale fitted with a jaw at one end. Another
jaw, containing the vernier scale, moves over the main scale. When the two jaws are
in contact, the zero of the main scale and the zero of the vernier scale should coincide.
If both the zeros do not coincide, there will be a positive or negative zero error.
After calculating the least count place the object between the two jaws.
Record the position of zero of the vernier scale on the main scale (3.2 cm in figure
below).
Principle of Vernier
You will notice that one of the vernier scale divisions coincides with one of the main
scale divisions. (In the illustration, 3rd division on the vernier coincides with a MS
division).
Reading of the instrument = MS div + (coinciding VS div x L.C.)
= 3.2 + (3 x 0.01)
= 3.2 + 0.03
= 3.23 cm
Instructions on use of a vernier caliper

The Vernier caliper is an extremely precise measuring instrument; the reading
error is 1/20 mm = 0.05 mm.

Close the jaws lightly on the object to be measured.

If you are measuring something with a round cross section, make sure that the
axis of the object is perpendicular to the caliper. This is necessary to ensure that
you are measuring the full diameter and not merely a chord.

Ignore the top scale, which is calibrated in inches.

Use the bottom scale, which is in metric units.

Notice that there is a fixed scale and a sliding scale.

The boldface numbers on the fixed scale are centimeters.

The tick marks on the fixed scale between the boldface numbers are millimeters.

There are ten tick marks on the sliding scale. The left-most tick mark on the
sliding scale will let you read from the fixed scale the number of whole
millimeters that the jaws are opened.

In the example above, the leftmost tick mark on the sliding scale is between 21
mm and 22 mm, so the number of whole millimeters is 21.

Next we find the tenths of millimeters. Notice that the ten tick marks on the
sliding scale are the same width as nine ticks marks on the fixed scale. This means
that at most one of the tick marks on the sliding scale will align with a tick mark
on the fixed scale; the others will miss.

The number of the aligned tick mark on the sliding scale tells you the number of
tenths of millimeters. In the example above, the 3rd tick mark on the sliding scale
is in coincidence with the one above it, so the caliper reading is (21.30 ± 0.05)
mm.

If two adjacent tick marks on the sliding scale look equally aligned with their
counterparts on the fixed scale, then the reading is half way between the two
marks. In the example above, if the 3rd and 4th tick marks on the sliding scale
looked to be equally aligned, then the reading would be (21.35 ± 0.05) mm.

On those rare occasions when the reading just happens to be a "nice" number like
2 cm, don't forget to include the zero decimal places showing the precision of the
measurement and the reading error. So not 2 cm, but rather (2.000 ± 0.005) cm or
(20.00 ± 0.05) mm.
MICROMETER SCREW-GAUGE
Micrometer screw-gauge is another instrument used for measuring accurately the
diameter of a thin wire or the thickness of a sheet of metal.
It consists of a U-shaped frame fitted with a screwed spindle which is attached to a
thimble.
The screw has a known pitch such as 0.5 mm. Pitch of the screw is the distance
moved by the spindle per revolution. Hence in this case, for one revolution of the
screw the spindle moves forward or backward 0.5 mm. This movement of the spindle
is shown on an engraved linear millimeter scale on the sleeve. On the thimble there is
a circular scale which is divided into 50 or 100 equal parts.
When the anvil and spindle end are brought in contact, the edge of the circular scale
should be at the zero of the sleeve (linear scale) and the zero of the circular scale
should be opposite to the datum line of the sleeve. If the zero is not coinciding with
the datum line, there will be a positive or negative zero error as shown in figure
below.
While taking a reading, the thimble is turned until the wire is held firmly between the
anvil and the spindle.
The least count of the micrometer screw can be calculated using the formula given
below:
Least count
= 0.01 mm
Determination of Diameter of a Wire
The wire whose thickness is to be determined is placed between the anvil and spindle
end, the thimble is rotated till the wire is firmly held between the anvil and the
spindle. The rachet is provided to avoid excessive pressure on the wire. It prevents the
spindle from further movement. The thickness of the wire could be determined from
the reading as shown in figure below.
Reading = Linear scale reading + (Coinciding circular scale x Least count)
= 2.5 mm + (46 x 0.01)
= (2.5 + 0.46) mm
= 2.96 mm
Relationship in the Metric system of length
1 kilometer (km) = 103 m
1 centimeter (cm) = 10-2 m
1 millimeter (mm) = 10-3 m
Mass
Mass is the quantity of matter contained in a body.
If you push a book, it moves faster than if you push a car with the same force. This is
because the car has more mass than the book. If you had two identical boxes, one
containing iron and the other containing cotton we could identify them by pushing the
boxes. We can say that the car and iron box are more reluctant to move than the book
and the cotton box. We call this reluctance to move "inertia". Larger the mass of an
object, larger is its inertia. Hence mass of a body is a measure of its inertia.
Moving objects have inertia too. A moving object needs force to make it stop. A
moving car has more inertia than a moving book. It needs more force to make it stop.
Measurement of Mass
Mass of an object can be determined by comparing the mass of it with a standard
mass. For this we can use a lever balance or a common balance.
Common Balance
This balance consists of a beam and two scale pans (shown in figure below), the beam
being balanced at its mid point on a knife-edge. The scale pans also hang on knife
edges and rest on the base board. When the balance is not in use the beam rests on the
beam support.
Figure 1: A Laboratory Balance
How to use a balance?
Use the leveling screws, attached beneath the base board to make sure that the beam is
horizontal. It can be verified with the help of the plumb- line provided shown in the
diagram.
Use the arrestment knob to raise the beam and the adjusting screw at the two ends of the
beam, to bring the pointer to the middle or zero mark on the scale.
Lower the beam using the arrestment knob again.
Place the body to be weighed on the left scale pan and put weights on the right hand scale
pan to balance the beam (when pointer is at zero).