IMPORTANT FORMULAE:
1.The three important equations of motion are:
V = u + at, where u = initial velocity
S = ut + ½ at2, v = final velocity
V2 - u2 = 2 as, t = time taken
a = acceleration produced
s = distance covered
2. Average speed = Total distance covered
...........................----------------------
............................. Total
time taken
3.Average velocity = 
= u + v
..................................------
.....................................
2
4. a = v - u
.........-----
........... t
5. V = w X r where v = linear velocity
w = angular velocity
r = radius of circle.
Class IX - Physics
Chapter - 2
Force and Acceleration
Points to Remember
1. Balanced forces: If the resultant of all the forces acting
on a body is zero, the force are called Balanced forces.
2. Unbalanced forces: If the resultant of all the forces, acting
on a body is not zero, the forces are called unbalanced forces.
3. Inertia: It is that property of a body due to which it resists
a change in its state of rest or of uniform motion.
4. Momentum: Of a body is defined as the product of its mass and
velocity.
Its S.I. unit is Kg m/s. it is a vector quantity.
5. Impulse: The impulse acting on a body is equal to the product
of force acting on the body and the time for which it acts.
Its S.I. unit is N-second ( Force is measured in Newton and time
in seconds)
6. Force of Friction: The force, which always opposes the motion
of one body over another body in contact with it, is called frictional
force.
7. Newton's First Law of Motion: A body at rest will remain at
rest, and a body in motion will continue in motion in a straight
line with a uniform speed, unless it is compelled by an external
force to change its state of rest or of uniform motion.
8. Newton's Second Law of Motion: The force acting on a body is
directly proportional to the produce of its `mass' and the 'acceleration'
produced in it by the action of the force, and it acts in the
direction of the acceleration.
9. Another definition of 2nd law of Motion: The force applied
to a body is directly proportional to the rate of change of momentum,
which it produces in the body.
10. Newton's third law of Motion: To every action there is an
equal and reaction.
11. Friction is a necessary evil.
12. Inertia is of two types: Inertia of Rest and Inertia of Motion.
IMPORTANT FORMULAE
1. Mathematical form of Newton's 2nd law of motion.
F = m x a where F = force, m = mass, a = acceleration
2. F = MV - MU = Pf - Pi where Pf = final momentum
........---------...-------
............. t............
t........... Pi = Initial momentum
3. I = F x t where I = Impulse, F = force, t = time
4. M = m x v, where M = momentum, m = mass and v = velocity.
CHAPTER -3
GRAVITATION
Points To Remember
1)Universal law of Gravitation - The gravitation force of attraction
between any two particles is directly proportional to the product
of the masses of the particles and inversely proportional to the
square of the distance between the particles. The direction of
the force is along the line joining the two particles.
2)The unit of `G' is Nm2/kg2 and its value
is 6.67 x 10-11 Nm2/kg2.
3)In the absence of air, all bodies irrespective of their masses
fall towards the earth with the same acceleration. This acceleration
is known as acceleration due to gravity. It is denoted by `g'.
On the earth's surface g = 9.8 m/s2.
4)Variation of `g' - the value of `g' is maximum at the surface
of earth. It decreases above and below the earth's surface.
5)Weight - The weight of a body is the force with which it is
attracted by the earth towards its center. It varies from place
to place. The Weight of a body on the moon is about 1/6 of its
weight on the earth.
7)Weightlessness - is experienced by an object falling freely
under gravity.
Projectile motion - When a body is thrown near the earth's surface
in a direction other than vertical, its motion is called projectile
motion.
8)Its path is parabolic for small speeds.
If a body is projected with high enough speed, it moves around
the earth as a satellite.
Newton's 3rd law of motion also applies to gravitational force.
IMPORTANT FORMULAE
1. Relation between 'g` & `G'.
g = GMe where Me = mass of earth
-----
R2c Rc
= Radius of earth
2.mathematical expression for Newton's law of gravitation
f = G m1 m2 , G = Gravitational
constant
---------
r2 m1,
m2 = masses of the two bodies
r
= distance between the two bodies
3. W = m x g, where w = weight of the body
m = mass of the body.
4. The three equations of motion for free fall under gravity.
(1) v = u + gt
(2) h = ut + ½ gt2
(3) v2 - u2 = 2gh
For bodies moving against gravity, the above equations of motion
are modified by replacing
g with (-g).
Class IX, Physics
Chapter - 4
SIMPLE PENDULUM AND RESTORING FORCE
POINTS TO REMEMBER
1. SIMPLE HASMONIC MOTION ( S.H.M.):Is that type of vibratory
motion in which the restoring force acting on the vibrating body
is directly proportional to its displacement.
2. SIMPLE PENDULUM: A small, heavy metallic bob suspended from
a rigid support by a light inextensible string is called a simple
Pendulum.
3. LENGTH OF THE PENDULUM: The length from the point of suspension
upto the center of the bob is called the length of the Pendulum.
4. AN OSCILLATION : The motion of a Pendulum bob from one extreme
position to the other extreme positive and then back to the first
extreme position constitutes one complete oscillation.
5. AMPLITUDE : The distance covered by the bob from mean positive
to an extreme position is called amplitude of the Pendulum.
6. TIME PERIOD: It is the time taken to complete one oscillation.
7. The time period of a simple pendulum depends upon its length
and the value of `g' at the place of experiment.
8. Force Acting on the bob of a simple Pendulum
(1) the pull of the string
(2) the pull of gravity
(3) the air friction
9. Damping :A gradual decrease in the amplitude of oscillation
is called damping. It is due to air resistance and the friction
at the support.
10. Restoring Force: A force which is always directed towards
the mean position during the oscillatory motive of the body is
called Restoring force Gravity and tension in the string together
provide restoring force in a pendulum.
11. Graph the L - T graph of a pendulum is parabolic where the
L-T2 graph is a straight line passing through the origin.
12. The time period of a simple pendulum is independent of
(1) mass of the bob
(2) material of the bob
(3) amplitude of oscillation
_____
13. T - 2 l Ö
L / g Where T = Time period of the simple pendulum
L = Length of simple Pendulum
G = acceleration due to gravity.
14. Every oscillatory motion is periodic but every periodic
motion is not oscillatory.
Class IX Physics
Chapter - 5
Waves
Points to remember
1. WAVE - A wave is a disturbance travelling through a medium
due to repeated oscillatory motion of the particles of the medium
about their mean positions, the motion being handed - over from
one particle to next progressively.
2. MECHANICAL WAVES AND ELECTROMAGNATIC WAVES - waves needing
a material medium to propagate are mechanical waves e.g. sound
waves, water waves. Waves not needing a medium to propagate are
called electromagnetic waves e.g. Radio waves, light waves.
3. LONGITUDINAL AND TRANSVERSE WAVES - It the particles of the
medium move along the direction of motion of the wave, the wave
is called a longitudinal wave .On the other hand if the particles
of the medium move perpendicular to the direction of motion of
the wave, the wave is called a transverse wave.
4. A PULSE - A disturbance, which is sudden and lasts only for
a short duration of time, is called a pulse.
5. WAVELENGTH - The distance between any two points on a wave,
which are in the distance between two consecutive crests and same
state of vibration, is called wavelength.
It is also the troughs on a transverse wave and between two consecutive
compressions or rare factions on a longitudinal wave.
6. Time Period - The time required to produce one complete wave
(or one vibration) is called time period.
7. FREQUENCY - The number of complete waves produced per second
is called frequency.
Its S.I. unit is Hertz.
8. Wave transports energy and not matter.
IMPORTANT FORMULAE
1. f = 1/T
2. V = l/T
3. V = lx F
F = frequency
V= velocity of wave
l = Wavelength
T = time period
Chapter - 6
Work and Energy
Points to Remember
1. Work - When a force acts on an object and the object moves,
work is done by the force on object. Its S.I. unit is Joules.
It is a scalar quantity.
2. Energy - The capacity of an object to do work is called energy
of the object.
Its S.I. unit is Joules. It is a scalar Quantity.
3. Kinetic energy - The ability of a body to do work by virtue
of its motion is called kinetic energy.
4. Potential energy - the ability of a body to do work by virtue
of its position or state of strain or configuration is called
its potential energy.
5. Mechanical energy - The sum of the Kinetic energy and potential
energy of the object is called its mechanical energy.
6. Power - rate of doing work or supplying energy is called power.Its
S.I unit is watts.1 horsepower =746 watts
7. Law of conservation of energy - Energy can neither be produced
nor be destroyed. It can only be changed from one form to another.
8. Escape velocity - The minimum speed with which an object should
be thrown so that it overcomes the gravitational pull of the earth
and escapes in space.
Important Formulae
1. W = Fd cos q where
w = work done by a force `F'
d
= displacement
q
= angle between the force & displacement
It displacement is perpendicular to the force, work done = 0
2. K.E = ½ mv2 where K E = Kinetic energy,
m - mass, v = velocity
3. Gravitational P.E = w = mgh
Where w = work done against gravity, m = mass, g = accelration
due to gravity, h = height, P.E. = Potential energy.
4. P = w/t = E/t where P = Power, E = energy, w = work, t =
time
___
5. V = 2 ÖGm =
escape velocity, G = universal Gravitational constant
r
M = mass of the earth, R = Radius of earth.
