while travelling on the bus, what do we feel when it stops or
moves
suddenly? Why does it happen? Such
types of
incidents felt by us in our daily life. In this lesson, we will
study about those
facts,
principles and rules related to them.

Definition:
Force is defined as the push or pull which change or tends
to change the position of the body
from rest to motion or from motion to rest. Or,
Force is an agent or influence that causes a free body to change
its state direction and shape / size. Its
unit is Newton. The force that is applied to a body of
mass one
kg to produce an acceleration of one m/s^{2} is known as
one newton.
1N = 1kg × 1m/s^{2}= 1 kgm/s^{2}

Balanced Force: When force acting on a body from
different direction do not change the states of rest or motion
of an object, then it is said to have balanced force. Its net
resultant is 0.

Unbalanced Force:
When force acting on a body from different direction changes the
state of rest or of motion , such forces are unbalanced force.
Its resultant is non-zero

REST AND MOTION

Key points:

They are relative terms. (The same object may be at rest
with respect to an object but in the motion with respect to
another object. for example: in moving bus, passengers are
at rest with respect to each other, but the bus and the
passengers are in motion with respect to the nearby trees,
poles, etc.)

None of the objects are absolutely at rest or in motion.

Whether an object is at rest or in motion, it depends on
observer.

Rest: An object is said to be in rest for an
observer if the position of the object does not
change with respect to the observer. We wait for
our school bus or sleep at night are some example of
rest.
To be an object in rest, it must not occupy any space.

Motion: An object is said to be in motion for an observer if
the position of the body changes with respect to the
observer. To be an object in motion, it must
occupy some space.
Flying aero plane, running car are some example of
bodies
in motion.
What is the relation between rest and motion?

Speed and
Velocity

The total distance covered by an object per
unit time in any direction is called its speed.
Its SI unit is meter per
second (m/s). Speed is a scalar quantity as it has only magnitude
but no direction. Formula: Speed=(total distance covered
in any direction) / (time taken)

The total displacement covered by an object per unit time is
called its
velocity. Its SI unit is meter per second (m/s).Velocity is
a vector quantity as it has both magnitude and direction. Formula: Velocity= (total displacement) / (time
taken)
Distance is scalar quantity but displacement
is vector, why?

Uniform-Velocity: If an object covers equal distance in equal
interval of time is called uniform velocity.
To become the uniform velocity, the direction of the speed must
have a fixed direction. It is not said a uniform velocity if an
object is moving
in a circle

Non-Uniform-Velocity: If an object covers unequal distance in
equal interval of time in a straight line in a fixed directions
called uniform velocity. Or, if it covers an
equal distance in each second in different directions, it is also
said to be
in non-uniform velocity.

Acceleration

The rate of change of velocity is called acceleration
Its unit in SI is m/s^{2}. Lets elaborate it with one example
If you apply more force on the peddle of your bicycle, the
velocity of the bicycle increases and if you apply the brake,
its velocity
decreases. Here, the motion of the bicycle is called accelerated
motion. Acceleration = (change in velocity) / Time taken
.
or, Unit of acceleration = (unit of velocity ) / (unit of time)
or, unit of acceleration = (m/s) / s
or, unit of acceleration=m/s^{2} Net acceleration = (final velocity
- initial velocity) / Time taken

- If the acceleration of an object is constant
throughout the motion is called uniform acceleration.

- If the acceleration of an object is not constant
throughout the motion is called non uniform
acceleration.

Equations of
Motion

let,
S = displacement
U = initial velocity
V = final velocity
A = acceleration
T = time
Now,

First Equation of Motion :
v = u+at
we know that,
a = (v - u) / t
v - u = at
v = u + at

2nd Equation Of Motion
s = {(u + v) / 2} × t
we know that,
a - v = (u + v) / 2
s/t = (u + v) / 2
s = {(u + v) / 2} × t.

3rd Equation Of Motion
v^{2} = u^{2} + 2as
we know that,
v = u + at
t = (v - u) / a
and, s = {(u + v) / 2} × t
Substituting the value, we get
s = {(u + v) / 2} × {(v - u) / a}
s = (v^{2} - u^{2}) / 2a
v^{2} - u^{2} = 2as
v^{2} = u^{2} + 2as

u Fourth Equation of Motion :
s = ut + 1/2(at^{2}) Derive yourself, if any
problem ask in question section.

Inertia

The tendency of a body to continue its state of rest or
uniform
motion in a straight line is called inertia. It is of
two
types:

INERTIA OF MOTION:

Anything that continue its state in motion or, the
inertia
presents in moving bodies is known as inertia of
motion. For example:Due to the inertia of motion, a fan keeps on
moving
for some time even
after the electricity is switched off. Electric fan runs
because
of electric
power, but it keeps on moving even after the electric supply
is
cut off.
The fan should be stopped as soon as the switch is off but
it
doesn’t stop
because of inertia of motion.

INERTIA OF REST:

Anything that continue its state in rest or, the inertia
presents in resting bodies is known as inertia of
rest.
For example:
Due to inertia of rest, a mango fruit falls down from the
branch
while
shaking it forcefully.
In the beginning, the fruit along with the branch remains at
rest. When
we shake the branch, it comes into motion, but due to
inertia of
rest, the
mango fruit tries to be at rest. As a result of inertia of
rest
of the fruit, it
detaches from the branch and falls down.

Newton's Law of Motion

The famous scientist, Newton, formulate the laws of motion by him
and it is now known as newton's laws of motion. He formulates
three laws of motion:

Newton's First Law of Motion:

According to Newton's First law of motion, "everybody
continues
to be in its state
of rest or uniform motion in a straight line unless an
external force is applied
on it". This law is fully depends on law of inertia. It
means that, force is required
to change the inertia of rest of a body into inertia of motion
and inertia of
motion of a body into inertia of rest. Hence, Newton’s first law
of motion
is also called law of inertia.

Newton’s Second Law of Motion

Newton’s second law of motion states that “acceleration produced
on
a body
is directly proportional to the force applied on it and
inversely
proportional
to its mass”

Mathematically,
-Acceleration(a) α Force(F){when mass of the body is kept
constant}
-Acceleration(a) α 1/m {if force is kept constant}
Hence, if force (F) produces an acceleration (a) in a body
having mass (m),
then from the newton’s second law of motion,
-Acceleration(a) α F / m
-F α ma
-F = kma(here k is a constant)
In equation (iii) if a = 1 m/s^{2}, m = 1 kg, the value of F
becomes 1N. So, in
this condition the value of k also becomes 1. Therefore; F = ma

Newton's Third Law of Motion:

Newton’s third law of motion states that “every action has
equal but opposite
reaction”.

Examples: -While launching a rocket into the space,
the hot gases produced by the
rapid burning of fuel rush downward but the rocket goes
upward.
-While firing a gun, bullet moves in the forward direction
but
the
gun recoils in the backward direction.

In case of any problem ask me in
qustions section!!!!