Impulsive force and Impulse of a force

1.Impulsive Force
An impulsive force is a very great force acting for a very short time on a body, so that the
change in the position of the body during the time the force acts on it may be neglected.
e.g.The blow of a hammer, the collision of two billiard balls etc.  
2.Impulse of a force
The impulse J of a constant force F acting for a time t is defined as
the product of the force and time.
i.e Impulse = Force × time
J = F × t
The impulse of force F acting over a time interval t is defined by the integral.
The impulse of a force, therefore can be visualized as the area under the force versus time
graph as shown in Fig above When a variable force acting for a short interval of time, then the
impulse can be measured as,
J = Faverage × dt
Impulse of a force is a vector quantity and its unit is N s.

Principle of impulse and momentum
By Newton’s second law of motion, the force acting on a body = m a
Where m = mass of the body and a = acceleration then
The impulse of the force = F × t = m a t
If u and v be the initial and final velocities of the body then,
           a = v-u/t
therefore, impulse of the force = m * v-u/t * t= mv - mu
i.e. Impulse = Final momentum of the body – initial momentum of the body
i.e. Impulse = Change in momentum
The above equation shows that the total change in the momentum of a body during a time interval is equal to the impulse of the force acting during the same interval of time. This is called principle of impulse and momentum.
Examples
(i) A cricket player while catching a ball lowers his hands in the direction of the ball.
If the total change in momentum is brought about in a very short interval of time, the average
force is very large according to the equation,
By increasing the time interval, the average force is decreased. It is for this reason that a cricket
player while catching a ball, to increase the time of contact, the player should lower his hand in
the direction of the ball, so that he is not hurt.
(ii) A person falling on a cemented floor gets injured more where as a person falling on a sand
floor does not get hurt. For the same reason, in wrestling, high jump etc., soft ground is
provided.
(iii) The vehicles are fitted with springs and shock absorbers to reduce jerks while moving on uneven or wavy roads.

Swine Flu

Image is from the courtesy of NASA

Newton 2nd law of Motion:
It states that- the rate of change of linear momentum of a body is proportional to applied force
and the change in momentum takes place in the direction of applied force.
Mathematically   F = ma
Where
 F is the applied force &  a is momentum of body. as we know that rate of change of velocity is acceleration.

Linear momentum

Linear momentum:
The quantity of motion contained in a body is called its linear momentum.
Linear momentum of a body is measured by the product of mass and velocity of the body.
i.e.
Momentum = mass × velocity
    p  =  mv
Note:
1. p is a vector quantity and has direction same as that of velocity.
2. Unit of p kgm/s  is ( in SI system) and gcm/s (in c.g.s. system)
3. Dimensional formula for
= [MLT-1]
4. If two bodies of unequal masses and velocities have same momentum, then
i.e.       p1  =p1
or     m1v1 = m2v2
Hence for bodies of same momenta, their velocities are inversely proportional to their masses.
Note: 1. If a car and a truck move with same velocity, the truck will have greater momentum
due to larger mass.
2. We prefer a heavy hummer to derive a nail into a board due to large mass; it will impart a
large momentum to the nail.

First Laws Of Motion and Inertia

Newton’s Law of Motion:
It is also called Law of Inertia. According to this law a body continues to be in the state of rest or
of uniform motion along a straight line unless it is acted upon by some external force.
Inertia:
Inertia is the property of a body by virtue of which it cannot change its state of rest or of
uniform motion along a straight line by itself.
Mass is the measure of inertia. The greater the mass, larger is the inertia and vice-versa.
Types of inertia:
Inertia is of three types:
1. Inertia of rest.
2. Inertia of motion.
3. Inertia of direction.
1. Inertia of rest: The property of a body by virtue of which it cannot change its state of rest,
is known as inertia of rest.
Examples:
i) When branch of a apple tree is shaken, apples fall down. This is because the
branch comes in motion but the apple tends to remain at rest due to inertia of rest.
ii) When a bus suddenly starts moving, the passenger tends to fall backward. This is
because the lower part of the body of the passenger comes in motion with bus but
the upper part tends to remain at rest due to inertia of rest.
2. Inertia of Motion: The property of a body by virtue of which it cannot change its state of
uniform motion along a straight line is known as inertia of motion.
Examples:
1) When a bus stops suddenly, the passenger tends to fall forward. This is because the
lower part of the body of the passenger comes at rest with bus but the upper part of the
body tends to remain in motion due to inertia of motion.
2) A person jumping out of a moving bus may fall forward. This is because the feet of the
person come at rest with ground but the upper part of body tends to remain in motion
due to inertia of motion.
3) An athlete running in a race will continue to run even after reaching the finishing point.
3. Inertia of direction: It is the inability of the body to change its direction of motion by itself.
Examples
When a bus moving along a straight line takes a turn to the right, the passengers are thrown
towards left. This is due to inertia which makes the passengers travel along the same straight
line, even though the bus has turned towards the right.

Motion

• One Dimensional Motion. The motion of an object is said to be one

dimensional motion if only one out of the three coordinates specifying the
position of the object changes with respect to times.
(an object moves along any of the three axes X, Y or Z).

•  Two dimensional motion. The motion of an object is said to be two

dimensional motion if two out of the three coordinates specifying the position
of the object change with respect to time. (the object moves in a plane.)

•  Three dimensional motion. The motion of an object is said to be three

dimensional motion if all the three coordinates specifying the position of
the object change with respect to time. (the object moves in space.)

•  Speed. The speed of an object is defined as the ratio of distance covered

and time taken i.e. speed = distance traveled/(time taken). Speed is a
scalar quantity. It can only be zero or positive.

•  Instantaneous velocity. The velocity of an object at a given instant of time

is called its instantaneous velocity. When a body is moving with uniform
velocity, its instantaneous velocity = average velocity = uniform velocity.

DIMENSIONS

We may define the dimensions of a physical quantity as the powers to which the
fundamental units of mass, length and time have to be raised to represent a derived unit
of the quantity.
For example,  For example,
 velocity = [L1 T-1] = [M0L1 T-1]
Hence the dimensions of velocity are: zero in mass, +1 in length and -1 in time. Hence the dimensions of velocity are: zero in mass, +1 in length and -1 in time.

DIMENSIONAL FORMULA
The expression which shows how and which of the base quantities represent the
dimensions of a physical quantity is called the dimensional formula of the given physical
quantity.
For example, the dimensional formula of the volume is [M° L3 T°],
and dimensional formula of speed or velocity is [M° L T-1].
Similarly, [M° L T–2] is the dimensional formula of acceleration and [M L–3 T°] that of
mass density.
DIMENSIONAL EQUATION:
An equation obtained by equating a physical quantity with its dimensional formula is
called the dimensional equation of the physical quantity.
For example, the dimensional equations of volume [V], speed [v], force [F] and mass
density [ρ] may be expressed as
[V] = [M0 L3 T0]
[v] = [M0 L T–1]
[F] = [M L T–2]
[ρ] = [M L–3 T0]

Application of Dimensional Analysis:
1. To check the correctness or consistency of a given formula
2. To derive relationship among various physical quantities.
3. To convert one system of unit into other system.

• To check the correctness or consistency of a given formula    
• The correctness or consistency or accuracy of a formula can be checked by
  applying the principle of homogeneity of dimensions. According to this principle
  dimensions of each term on the both sides of the formula is always same.
  Example: to check the accuracy of v2 –u2 = 2as
  Solution:
  The dimensions of LHS = [LT-1]2 - [LT-1]2 = [L2 T-2] - [L2 T-2] = [L2 T-2]
  The dimensions of RHS = 2aS = [L T-2] [L] = [L2 T-2]
  The dimensions of LHS and RHS are the same and hence the equation is dimensionally correct.
•  
•  
• 2. To derive relationship among various physical quantities.
  Let a physical quantity Q depends upon the quantities q1 , q2, and q3 such that:
  Q ∝ Š VŠ Š W
  Or Q = k Š VŠ Š W ← (1)
  Where k is dimensionless constant.
  Now, we will apply the following steps -
  i) Write dimensional formula of each quantity on both sides of equation (1)
  ii) Equate the powers of M, L and T and solve three equations so obtained
  and find a, b and c.
  iii) Now we will put the values of a, b and c in equation (1), hence we get a
  new physical relation(formula)
   
• 3. To convert one system of unit into other system.
  Let M1 ,L1 and T1 are fundamental units of mass, length and time in one system of unit.
  & M2 ,L2 and T2 are fundamental units of mass, length and time in another system.
  Let a, b and c be the dimensions of the given quantity in mass, length and time
  respectively.
  If n1 is the numerical value of the quantity in one system then that n2 in other system is
  given by the formula:
  n2 = n1’“
  “
   
•  
• Limitations of Dimensional Analysis:
  1. Using dimensional analysis we cannot find the value of dimensionless constant.
  2. We cannot derive the relation containing exponential and trigonometric
  functions.
  3. It cannot inform that whether a quantity is scalar or vector.
  4. It cannot find the exact nature of plus or minus, connecting two or more terms in
  formula.
  5. The relation containing more than three physical quantities cannot be derived
  using dimensional analysis.

SIGNIFICANT FIGURES

Significant figures in the measured value of a physical quantity gives the number of digits in which we have confidence. Significant figures may be defined as the reliable digits plus the first uncertain digit are known as significant digits or significant figures. Larger the number of significant figures obtained in a measurement, greater is the accuracy of the measurement and vice-versa.

RULES FOR COUNTING THE SIGNIFICANT FIGURES:

• All the non-zero digits are significant. e.g 1254 has four significant figures

• All the zeros between two non-zero digits are significant, no matter where the decimal point is, if at all. e.g 1004 has four significant figures

•  If the number is less than 1, the zero(s) on the right of decimal point but to the left of the first non-zero digit are not significant. [In 0.00 2308, the underlined zeroes are not significant].

• The terminal or trailing zero(s) in a number without a decimal point are not significant. [Thus 145 m = 14500 cm = 145000 mm has three significant figures, the trailing zero(s) being not significant

•  The trailing zero(s) in a number with a decimal point are significant. [The numbers 8.500 or 0.007900 have four significant figures each.]

• Rounding off the Uncertain Digits

1. Preceding digit is raised by 1 if the insignificant digit to be dropped (the underlined digit in this case) is more than 5, and is left unchanged if the latter is less than 5.

4.356 = 4.36 (on rounding off up to three significant digits)
4.357 = 4.35 (on rounding off up to three significant digits)

1.  But if the insignificant digit is 5 then if the preceding digit is even, the insignificant digit is simply dropped and, if it is odd, the preceding digit is raised by 1.

5.3245 = 5.324 (on rounding off up to four significant digits)
5.3275 = 5.328 (on rounding off up to four significant digits)

Combination of Errors

• a) Error of a sum or a difference

Suppose Z = A + B. --------------(i)

Let ΔA = absolute error in measurement of quantity A
ΔB = absolute error in measurement of quantity B
 ΔZ = absolute error in sum Z of A and B.
Then A ± ΔA = measured value of A
B ± ΔB = measured value of B.
Z ± Δ Z = measured value of sum Z of A and B.
So, (i) becomes
Z ± Δ Z = (A ± ΔA) + (B ± ΔB)
Z ± Δ Z = (A+ B ) ± (ΔA+ ΔB)
Or Δ Z = ± ΔA± ΔB
So possible errors in Z are +ΔA+ ΔB, -ΔA+ ΔB, +ΔA- ΔB, -ΔA- ΔB.
& maximum possible error in Z = ± (ΔA+ ΔB)
Similarly, for the difference Z = A – B, we have
Z ± Δ Z = (A ± ΔA) – (B ± ΔB)
= (A – B) ± ΔA ± ΔB
or, ± ΔZ = ± ΔA ± ΔB
The maximum value of the error ΔZ is again Z = ± (ΔA+ ΔB)
Hence the rule : When two quantities are added or subtracted, the absolute error in
the final result is the sum of the absolute errors in the individual quantities.

• (b) Error of a product or a quotient

Suppose Z = A B. -------------- (i)
Let ΔA = absolute error in measurement of quantity A
ΔB = absolute error in measurement of quantity B
 ΔZ = absolute error in product Z of A and B.
Then A ± ΔA = measured value of A
B ± ΔB = measured value of B.
Z ± Δ Z = measured value of product Z of A and B.
Z ±ΔZ = (A ± ΔA) (B ± ΔB)

             = AB ± B ΔA ± A ΔB ± ΔA ΔB.
Dividing LHS by Z and RHS by AB we have,

Since ΔA and ΔB are small, we shall ignore their product.
Hence the maximum relative error
ΔZ/ Z = (ΔA/A) + (ΔB/B).
Similarly, for division we also have ΔZ/ Z = (ΔA/A) + (ΔB/B
Hence the rule: When two quantities are multiplied or divided, the relative error in
the result is the sum of the relative errors in the multipliers.

ERRORS

• ERROR: 
• The difference between true value and measured value is known as error in measurement.

• Accuracy: The accuracy of a measurement is a measure of how close the measured value is to the true value of the quantity.

• Precision: precision tells us to what limit the quantity is measured.

Types of Errors
Errors may be divided into following three types
(I) systematic errors and
(II) Random errors.
(III) Gross errors

(I) Systematic errors:- The systematic errors are those errors that tend to be in one direction, either positive or negative. Some of the sources of systematic errors are :
(a) Instrumental errors that arise from the errors due to imperfect design or zero
error in the instrument, etc. For example, in a vernier callipers the zero mark of vernier scale may not coincide with the zero mark of the main scale, or simply an ordinary metre scale
may be worn off at one end.
(b) Imperfection in experimental technique or procedure To determine the temperature of a human body, a thermometer placed under the armpit will always give a temperature lower than the actual value of the body temperature.
(c) Personal errors that arise due to an individual’s bias, lack of proper setting of the
apparatus or individual’s carelessness in taking observations without observing
proper precautions, etc. For example, if people, by habit, always hold your head a bit too far to the right while reading the position of a needle on the scale, you will introduce an error due to parallax.


(II) Random errors or Chance Errors
The random errors are those errors, which occur irregularly and hence are random with
respect to sign and size. These can arise due to random and unpredictable fluctuations
in experimental conditions (temperature, voltage supply etc).
For example, when the same person repeats the same observation, he may get different
readings every time.
(III) Gross Error:
The errors due to carelessness of the observer are known as Gross Errors. e.g. Recording
the observations wrongly, using the wrong values of observations in calculations.
Least Count: The smallest value that can be measured by the measuring instrument is
called its least count. All the readings or measured values are good only up to this value.

Least count error The least count error is the error associated with the resolution of the
instrument. For example, a vernier callipers has the least count as 0.01 cm; a
spherometer may have a least count of 0.001 cm.
Least count error belongs to the category of random errors but within a limited size; it
occurs with both systematic and random errors.
Using instruments of higher precision etc., we can reduce the least count error.
Main Point: Repeating the observations several times and taking the arithmetic mean of
all the observations, the mean value would be very close to the true value of the
measured quantity.
Absolute Error, Relative Error and Percentage Error
Absolute Error: The magnitude of the difference between the true value of the quantity
and the individual measurement value is called the absolute error of the measurement.
This is denoted by | Δa |.
If true value is not known then we considered arithmetic mean as the true value. Then
the errors in the individual measurement values are
Ea1 = amean – a1,
Fa2 = amean – a2,
.... .... ....
.... .... ....
Fa n = amean – an
Mean absolute error: The arithmetic mean of all the absolute errors is taken as the final
or mean absolute error of the value of the physical quantity a. It is represented by
Δamean.
Thus,
Δamean = (|Δa1|+|Δa2 |+|Δa3|+...+ |Δan|)/n
Relative Errors: The relative error is the ratio of the mean absolute error Δamean to the
mean value amean of the quantity measured.
Relative error = Δamean /amean
Percentage Error: When the relative error is expressed in per cent, it is called the percentage error (δa).
Thus, Percentage error δa = (Δamean/amean) × 100%

 

Parallax Method:

• Parallax Method:

This method is used to determine distance of stars which are less than 100 light years
away .
Let we have to find out the distance (d) of a nearby star N. let A and B are the two
positions of earth revolving around the sun. The position B is diametrically opposite to
position A.
Let F is any star at very large distance from the earth such that its direction and position
w.r.t. earth remains constant.
Now ∠FAN = ∠ANS = θ1 ( Alternate angles)
& ∠FBN = ∠BNS = θ2 ( Alternate angles)
Therefore,∠ANB = ∠ANS + ∠BNS
= θ1 + θ2
As, )*567 %     
89:
;    θ1 + θ2 = AB/AN

<
Hence by knowing θ1 and θ2 we can calculate AN = BN =d.
Size of Moon or Planet:
Let r = distance of planet or moon from the earth.
θ = angle subtended by diameter AB of planet or moon at any point on the earth.

As, angle =     
89:
= θ = #

= θ = >

or d = θ r
Hence, the diameter ‘d’ can be calculated by measuring ‘θ ’ and using ‘r’
Numerical: Find the value of following in radians.(i) 1O (ii) 1’ (iii) 1’’
(i) 1o =

radian = 1.745 10-2 radian
(ii) 1’ = 8 ?

= 1.745 10-2/60 radian @ 2.91 10-4 radian
(iii) 1’’ = A9B:

= 2.91 10-4 /60 radian @ 4.85 10-6 radian

MEASUREMENT OF LENGTH

• MEASUREMENT OF LENGTH

Length can be measured by (1) Direct Methods or by (2) Indirect Method.
Direct Methods:
These methods involves the use of
i. metre scale ( 10 RISE TO POWER-3 m to 10 RISE TO POWER 2m)
ii. vernier calipers (up to 10 RISE TO POWER -4m)
iii. screw gauge ( up to 10 RISE TO POWER -5m)
Indirect Method:
Beyond the range 10 RISE TO POWER -5 to 10 RISE TO POWER 2 we use indirect methods.

• REFLECTION METHODS

1. Echo Method: It is method used to find the distance (x) of a hill from a given point. In this method sound wave sent from the point of observation P to hill. The sound wave is reflected back by hill. By finding the time difference (t) between transmissions of sound and heard of echo.
The distance travelled by sound wave = x + x = v × t
⇒ 2x = v × t
⇒ x =        

Hence we can find x using x =        

, where v is velocity of sound.

2. Laser Method: It is used to find the distance of moon from earth. The laser beam is transmitted from earth is received back on earth after reflection from moon. The time interval (t) between transmission and reception of beam is measured.
If c = velocity of Laser
Then distance = velocity × time
x +x = c × t
2x = c × t
Or x =        

Where x = distance between earth and moon.
3. Sonar Method: (Sound Navigations and Ranging): This method is used to find the depth of ocean and to locate submarine inside the water. In this method ultrasonic waves are sent through ocean from transmitter to submarine. These ultrasonic wav are reflected from the submarine. By finding the time difference (t) between
transmitted and reflected waves, the distance x of submarine can be find using the formula

x =  c * t/ 2

ADVANTAGES OF SI Units

• ADVANTAGES OF SI Units
• SI is one of the largest system of unit. It has many advantages over other system of units like MKS or FPS or CGS. Few of them are enlisted below

1. SI is a coherent system of units i.e. a system based on a certain set of fundamental

units, from which all derived units are obtained by multiplication or division without

introducing numerical factors i.e. units of a given quantity are related to one another

by powers of 10.

2. SI is a rational system of units, as it assigns only one unit to a particular physical

quantity.

For example joule is the unit for all types of energy. This is not so in other systems of

units. e.g. in MKS system, mechanical energy is in joule, heat energy is in calorie and

electric energy is in watt hour.

3. SI is an absolute system of units. There are no gravitational units on the system.

The use of factor ‘g’ is thus eliminated.

4. S.1 is a metric system i.e. the multiples and sub multiples of units are expressed as

powers of 10.

5. In current electricity, the absolute units on the S.I, like ampere for current, volt for

potential difference, ohm for resistance, Henry for inductance, farad for capacity arid

so on, happen to be the practical units for measurement of these quantities.

6. SI is an internationally accepted system

SOME MORE COSMOLOGICAL  UNITS OF DISTANCE:
1. Astronomical Unit (A.U.) : The average distance between the centre of the sun
to the centre of the earth is known as one A.U.
1 A.U. = 1.496* 10 RACE TO POWER 11
 1.5 1011 m
2. Light Year (l.y.) : One light year is the distance travelled by light in vacuum in
one year.
1 l.y. = 3* 10 RACE TO POWER 8 * (365* 24  *60 * 60)
= 9.46 * 10 RACE TO POWER 15 m
3. Par sec (Parallactic Second): One Par sec is the distance at which an arc of 1A.U.
long subtends an angle of 1 second.
1 Parsec = 3.084* 10 RACE TO POWER 16 m

THE INTERNATIONAL SYSTEM OF UNITS

SI System: - It is an International system of unit. S.I. stands for It based upon seven fundamental, two supplementary and a large no. of derived units

SI Base Quantities and Units:-

Length :- metre m The metre is the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second. (1983)
Mass:- kilogram kg The kilogram is equal to the mass of the international prototype of the kilogram (a platinum-iridium alloy cylinder) kept at international Bureau of Weights and Measures, at Sevres, near Paris, France. (1889).
Time:- second s The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.
(1967).
Electric Current:- ampere A The ampere is that constant current which, if maintained in current two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2×10–7 newton per metre of length. (1948)
Temperature:- kelvin K The kelvin, is the fraction 1/273.16 of the thermodynamic dynamic temperature of the triple point of water. (1967) Temperature
Amount of Substance:- mol The mole is the amount of substance of a system, which contains substance as many elementary entities as there are atoms in 0.012 kilogram of carbon - 12. (1971)
Luminous Intensity:- candela cd The candela is the luminous intensity, in a given intensity direction, of a source that emits monochromatic radiation of frequency 540 Tera hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. (1979)

Supplementary Units:
(a) Plane angle dθ is defined as the ratio of length of arc ds to
the radius r .
(b) Solid angle dΩ is defined as the ratio of the intercepted area
dA of the spherical surface, described about the apex O as the
centre, to the square of its radius r, as shown in fig. (b)
The unit for plane angle is radian with the symbol rad and the unit for the solid angle is steradian with the symbol sr. Both these are dimensionless quantities.

Unit & Measurements

•  INTRODUCTION

Quantity:- Anything which can be measured is called quantity.
Phycical Quantity :-A quantity in terms of which law of physics can be expressed and can be
measured directly or indirectly is called physical quantity.
Types of Physical Quantities:
(i) Fundamental Quantities.
(ii) Derived Quantities
(i) Fundamental Quantities:- The quantities which cannot be derived from other
quantities called fundamental quantities. - e.g. mass, length and time.
(ii) Derived Quantities:- The quantities which can be derived from fundamental physical
quantities are called derived physical quantities. E.g. velocity, acceleration, force etc

Unit:- Unit of a physical quantity may be defined as the standard of its measurement.
If Q = quantity
u = unit of quantity
Then Q = nu
Where n = no. of times the unit u is contained in Q.

(I) Fundamental Units:- The units of those quantities which can not be derived from
other physical quantities are called fundamental units. e.g. units of mass, length, time
etc.
(ii) Derived Units:- The units of those quantities which can be derived from other
physical quantities are called derived units. e.g. units of velocity, acceleration., force etc.

Characteristics of a Unit :
A unit should have the following character
1. It should be well defined.
2. It should be a suitable size.
3. It should be easily accessible.
4. It should be easily reproducible.
5. It should not change with time.
6. It should not change with change in physical conditions like temperature, pressure etc.
System of Units :
A complete set of fundamental and derived units for all kinds of the quantities is called system of units.
Some common system of Units:
1. F.P S. System: - It is a British Engineering system based upon foot, pound, and second an the
fundamental unit of length, mass, and time.
2. C.G.S. System :- It is based on centimeter, gram and second as the fundamental unit of length, mass
and time.
3. M.K.S. System: - It is based on meter, kilogram and second as the fundamental
Unit of length, mass and time

Physical World Units and measurements

 PHYSICAL WORLD

• SCIENCE:

The word science has been derived from a Latin word ‘scientia’ which means ‘to know’. Hence, science may be defined as the systematic study of facts, events and happenings around us is called science.

• PHYSICS:

The word physics has been derived from a Greek word ’fusis’ which means ‘nature’. Hence, physics may be defined as the branch of science which deals with the study of nature and natural phenomena.

• SCIENTIFIC METHOD:

To know fully about anything we have to use the following steps:
1. Systematic observations
2. Controlled experiments
3. Qualitative and quantitative reasoning
4. Mathematical modeling
5. Prediction and verification of theories
These steps taken together are known as scientific method.

• UNIFICATION

Effort to explain different physical phenomena in terms of a few concepts and laws in physics is known as
unification. For example, the same law of gravitation  describes the fall of an apple to the ground, the
motion of the moon around the earth and the motion of planets around the sun.

• REDUCTION

Effort is to derive the properties of a bigger, more complex, system from the properties and interactions of its
basic simpler parts is called reduction or reductionism. For example, the subject of thermodynamics, developed in the nineteenth century, deals with bulk systems in terms of macroscopic quantities such as temperature, internal energy, entropy, etc.

• SCOPE OF PHYSICS

The idea of scope of physics can be obtained by study of following three domains  in physics:
1. Macroscopic domain: It deals with the study of large bodies and their phenomena. E.g. astronomical
phenomena and terrestrial phenomena.
2. Microscopic domain: it deals with the study of very small particles like electron, protons, neutrons, α-
particles and structure of atom.
3. Mesoscopic domain: It deals with the study of a few tens or hundreds of atoms.
It covers a very large range of magnitude of physical quantities like length, mass, time, energy, etc.
e.g. range of length is from 10 race to power-14m (study of electrons etc.) to 1026m (size of universe).Range of time is from 10 race to power -22s (time taken by light to cross nuclear diameter) to 10 race to power18s ( age of sun).The range of masses goes from, 10 race to power-30 kg (mass of an electron) to 10 race to power 55 kg (mass of known  observable universe)

• EXCITEMENT OF PHYSICS

Physics is exciting in many ways as-
1. A large number of complex phenomena of nature can be explained on the basis of some fundamental
laws of physics.
2. Physics has opened and detected many secrets of nature.
Except these reason for excitement of physics can vary from person to person.

• HYPOTHESIS, AXIOMS AND MODELS

A hypothesis is a supposition without assuming that it is true. It cannot be proved but it can be verified. e.g. The universal law of gravitation, because it cannot be proved. It can be verified and substantiated by experiments and observations. An axiom is a self-evident truth Model is a theory proposed to explain observed phenomena. For example Bohr’s model of hydrogen atom, in which Bohr assumed that an electron in the hydrogen atom follows certain rules

• PHYSICS, TECHNOLOGY AND SOCIETY

Technology is the application of the laws in physics for practical purposes.
The invention of steam engine, nuclear reactors, Production of electricity from solar energy and geothermal
energy had a great impact on human civilization. Also, physics giving rise to technology is the integrated chip( IC) and processors which grew the computer industry greatly in the last two decades. Computers have improved production techniques and lower production costs. The lawful purpose of technology is to serve people. Our society is becoming more and more science-oriented. We can become better members of society by understanding of the basic laws of physics.

• LINK BETWEEN TECHNOLOGY AND PHYSICS

Technology Scientific principle(s)
Aeroplane Bernoulli.s principle in fluid dynamics
Computers Digital logic
Electric generator Faraday.s laws of electromagnetic induction
Electron microscope Wave nature of electrons
Hydroelectric power Conversion of gravitational pot. energy into electrical energy
Lasers Light amplification by stimulated emission of radiation
Non-reflecting coatings Thin film optical interference
Nuclear reactor Controlled nuclear fission
Optical fibers Total internal reflection of light
Particle accelerators Motion of charged particles in electromagnetic fields
Photocell Photoelectric effect
Production of ultra high magnetic fields Superconductivity
Radio and Television Generation, propagation and detection of e.m. waves

• FUNDAMENTAL FORCES IN NATURE

Sir Issac Newton was the first who give an exact definition for force.“Force is the external agency applied on a body
to change its state of rest and motion”.
There are four basic forces in nature.
1. Gravitational force
2. Electromagnetic force
3. Strong nuclear force and
4. Weak nuclear force.

• 1. Gravitational force

Newton’s law of gravitation, the gravitational force of attraction between any two bodies in universe is directly
proportional to the product of the masses and inversely proportional to the square of the distance between them.
Properties:
1. It is the force between any two objects in the universe.
2. It is an attractive force by virtue of their masses.
3. By Gravitational force is the weakest force among the fundamental forces of nature but control the
structure of universe
4.  Unlike the other forces, gravity works universally on all matter and energy, and is universally attractive.
5. Carrier of these forces is Graviton.

• 2. Electromagnetic force

It is the force between charged particles such as the force between two electrons, or the force between two
current carrying wires.
Properties:
1. It is attractive for unlike charges and repulsive for like charges.
2. The electromagnetic force obeys inverse square law.
3. It is very strong compared to the gravitational force.
4. It is the combination of electrostatic and magnetic forces.
5.Carrier of these forces is Photon.

• 3. Strong nuclear force

This force holds the protons and neutrons together in the nucleus of an atom. It is the strongest of all the basic forces of nature. It, however, has the shortest range, of the order of 10−15 m. Carrier of these forces are mesons and pions.

• 4. Weak nuclear force

Weak nuclear force is important in certain types of nuclear process such as β-decay. This force is stronger than the gravitational force but much weaker than strong nuclear force.