phy 3...............

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Romesa’s notes for class matric
CHAPTER NO. 3

PHYSICS NOTES

CLASS MATRIC

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Q: define rest and motion.
Ans:
REST
It can be defined as:
“A body is said to be in rest if it
does not change its position with
respect to its surroundings”
MOTION
It can be defined as:
“A body is said to be in rest if it
changes its position with respect
to its surroundings”

Roka hoa matlab in rest

Motion matlab harkat mai

Q: define motion and its types.
Ans:
MOTION
It can be defined as:
“A body is said to be in rest if it changes
its position with respect to its
surroundings”
TYPES OF MOTION
There are 3 most common types of motion
1. Translator motion
2. Rotatory motion
3. Vibratory motion

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TRANSLATORY MOTION:

When a body moves in some particular paths such as linear,
circular or random. The body is said to be in rotatory motion.
e.g.
1.
a car moving on a straight
road
2.
an electron revolving
around the nucleus
3.
the Brownian motion
there are further 3 types of translatory
motion
1.linear motion
2.circular motion
3.random motion

ROTATORY MOTION:
When a body spins about its own axis
then the body is said to be in rotatory
motion.
e.g.
1.

rotation of earth

2.

motion of fan

VIBRATORY/ OSCILLATORY MOTION:

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When a body repeats its mean position in
equal interval of time then it is said to be in
vibratory or oscillatory motion.
OR
When a body possess TO and FRO motion
then it is said to be in vibratory or oscillatory motion.
e.g.
1. motion of pendulum
2. motion of a swing
Q: define translator motion and its types.
Ans:
TRANSLATORY MOTION
When a body moves in some particular paths such as linear,
circular or random. The body is said to be in rotatory motion.
e.g.
1. a car moving on a straight road
2. an electron revolving around the nucleus
3. the Brownian motions.
TYPES OF TRANSLATORY MOTION
There are 3 types of translatory motion

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1.linear motion
2.circular motion
3.random motion

LINEAR MOTION:
When a body moves in a straight path then it is
said to be in linear motion
e.g.
a car moving in a straight line

CIRCULAR MOTION:
When a body moves in a circular path then it is said to be in
circular motion
e.g.
earth revolving around the sun

RANDOM MOTION:

When a body moves in a zig zag path then it is said to be in
random motion.
e.g.
the Brownian motions.

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Q:Define kinematics.
Ans:
KINEMATICS
The word kinematics derived from Greek word 'kinema' meaning
motion. The branch of physics which deals with the motion of
objects without any reference to the force or agent causing the
motion is called kinematics.
Q: define mechanics.
Ans:
MECHANICS
Mechanics is the branch of physics that deals with the kinematics
and dynamics of objects.
Q: define dynamics.
Ans:
DYNAMICS
The word dynamics is taken from a Greek word 'dynamic'
meaning power. So dynamics is the branch of physics which deals
with the causes of motion or the factor which affect the motion.
Q.4: Define scalar and vector quantities with examples?
Ans:
SCALAR QUANTITIES
The quantities that are fully described by a magnitude (or
numerical value) alone are called scalar quantities.

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e.g.
•
•
•
•
•
•

time
speed
distance
work energy
temperature
charge
etc
VECTER QUANTITIES

The quantities that are fully described by both a magnitude and a
direction are known as vector quantities
e.g.
•
•
•
•
•
•
•

acceleration
velocity
displacement
force
weight
torque
momentum
etc

Q: define speed.
Ans
Speed
The rate of change of distance is called speed.

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Or
the rate at which someone or something
moves or operates or is able to move or
operate is called speed.

FOMULA

TYPES OF SPEED
the three types of speed are as follow
1. UNIFORM SPEED
2. VARIABLE SPEED
3. AVERAGE SPEED
UNIFORM SPEED
If a body covers equal distance in equal intervals of time then it is
said to be moving at uniform speed.

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VARIABLE SPEED
Variable speed is the distance covered by a body with
a speed which changes for a given time interval.
AVERAGE SPEED
the average of the speed of a moving object for the overall
distance is called average speed.
Q: define velocity.
Ans
VELOCITY
The rate of change of displacement is called velocity.
Or
the VELOCITY of something in a given direction.
FORMULA

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VELOCITY

TYPES OF VELOCITY
the three types of VELOCITY are as follow
1. UNIFORM VELOCITY
2. VARIABLE VELOCITY
3. AVERAGE VELOCITY
UNIFORM VELOCITY
If a body covers equal distance in equal intervals of time then it is
said to be moving at uniform VELOCITY.
VARIABLE VELOCITY
Variable VELOCITY is the distance covered by a body with
a VELOCITY which changes for a given time interval.
AVERAGE VELOCITY

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the average of the VELOCITY of a moving object for the overall
distance is called average VELOCITY.
Q: define acceleration.
ANS:
ACCELERATION
The rate of change of velocity is called
acceleration
• It is a vector quantity
• It can be calculated as a=v/t
• Its SI unit is m/s2
TYPES OF ACCELERATION
There are following types of acceleration
POSITIVE ACCELERATION
Positive acceleration is the change in velocity of an object in
the positive direction, as defined for the system.
NEGATIVE ACCELERATION
Negative acceleration is the change in velocity of an object in
the negative direction, as defined for the system.

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UNIFORM ACCELERATION
If an object's speed (velocity) is increasing at a constant rate
then we say it has uniform acceleration.
Q: define deceleration or retardation.
Ans:
DECELERATION/RETARDATION
The negative of acceleration is called
deceleration or retardation.
• It is a vector quantity
• It can be calculated as -a=v/t
• Its SI unit is m/s2
Q:define motion under gravity.
Ans:
MOTION UNDER GRAVITY
when an object appears to be falling under
the influence of gravity then the motion is
said to be the motion under gravity.
• Where distance (s) changes into height
(h) and acceleration (a) changes into
gravitational acceleration (g).
Q: define gravitational acceleration and sign convension
of gravitational acceleration (g).

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Ans:
Gravitational Acceleration
the acceleration due to gravity is known as
gravitational acceleration.
• It is represented by g
• Its SI unit is m/s2
• Its value is 9.8 m/s2 (g=9.8 m/s2)
SIGN CONVENSION OF g
• The value of g is taken as positive when the object moves
upwards to downwords
• The value of g is taken as negative when the object moves
downwords to upwards
• The value is 9.8 m/s2 (g=9.8 m/s2)
• Its SI unit is m/s2

SNO

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2
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DIFFERENCES
SPEED
VELOCITY
The rate of change of
distance is called speed

It is a scalar
quantity
It can never be negative
or zero
It is the distance
covered per unit time

The rate of change of
displacement is called velocity

It is a vector quantity
It can be negative or zero
It is the displacement covered
per unit time

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SNO

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2
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4

DISTANCE DISPLACEMENT
the length of a path
between any 2 points is
called distance
It is a scaler quantity

The shortest distance is called
displacement

It can never be negative
or zero
It is denoted by s

It can be negative or zero

It is a vector quantity

It is denoted by v

Q: derive equations of motion.
Ans:
EQUATION OF MOTION:
Relation among velocity, distance, time and acceleration is called
equations of motion. There are three equations of motion:
First Equation of Motion:
The final velocity (vf) of a moving object with uniform
acceleration (a) after time, t.
Let, the initial velocity = Vi.
Final velocity = Vf.
Time = t
Acceleration = a
We know that, Acceleration (a) =Change in velocityTime
taken=Change in velocityTime taken

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⇒a=Final velocity-Initial velocityTime taken
⇒a=Final velocity-Initial velocityTime taken
⇒a=Vf−Vit
⇒a=Vf-Vit
⇒at=Vf−Vi
⇒at=Vf-Vi
⇒at−Vf=−Vi
⇒at-Vf=-Vi
⇒−Vf=−Vi−at
⇒-Vf=-Vi-at
⇒Vf=Vi+at
⇒Vf=Vi+at ---(i)
This equation is known as first equation of
motion.

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Second Equation of Motion
Distance covered in time (t) by a moving body.
Let, Initial velocity of the object = Vi
Final velocity of the object = Vf
Acceleration = a
Time = t
Distance covered in given time = s
We know that,
Average velocity =Initial velocity+Final velocity
2
=Initial velocity+Final velocity
2
∴ Average velocity =Vi+Vf =Vi+Vf----(ii)
2
2
We know that, Distance covered (s) in given time = Average
velocity x Time
Or, s = Average velocity x Time -----------------(iii)
After substituting the value of average velocity from equation (ii)
we get
⇒s=Vi+Vf×t
2

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⇒s=Vi+Vf×t
2
After substituting the value of ‘Vf’ from first equation of motion
we get,
⇒s=Vi+(Vi+at)×t
2
⇒s=Vi+(Vi+at)×t
2
⇒s=Vi+Vi+at×t
2
⇒s=Vi+Vi+at×t
2
⇒s=2Vi+at×t
2
⇒s=2Vi+at×t
2
⇒s=2Vit+at2
2
⇒s=2Vit+at2
2
⇒s=2Vit +at2
2
2

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⇒s=Vit+1at2
2
The above equation is known as Second equation
of motion.
Third Equation of Motion
The third equation of motion is derived by substituting the value
of time (t) from first equation of motion.
We know the formula of distance s=Vav x t
As we know
Vav=Vi+Vf
2
Therefore; s=( Vi+Vf ) x t
2
Since; t=Vf-Vi
a
Therefore by substituting the values we get
S=( Vi+Vf ) x ( Vf-Vi )
2
a
S=( Vf+Vi ) x ( Vf-Vi )
2a
since;(a+b)(a-b)=a2+b2

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S=Vf2 – Vi2
2a
2aS= Vf2 – Vi2
This is called the Third equation of motion

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