#class9 Newton's laws complete summary #Learning the infamous newton laws of motion through fascinating narrative and storyline #simple easy explanation

1. 123
“ what exactly
causes the
motion “
Lets understand the cosmos
Before we begin , Be skeptical
and ask more questions
To understand motion and the
universe , lets follow the thread
along the legends like NEWTON
(who unified the theories) ,
curious GALILEO and genius
EINSTEIN

2. Name :
Nithyasri.S
Class & Sec
: IX-H
o Physics really began when we started the quench to understand motion and
manipulate it

3. This is one of the famous quotes of newton , these
Giants who invested their lifetime in anwering the
truths about the universe are Copernicus , Kepler ,
Galileo
( and many astronomers & physicists)

4. Birth of Aristotle’s
argument
Lets go back in time , when GALELIO tried to understand motion and
what causes it . He tried to quantify and measure motion like never before
Around
1600’s
The natural state
of objects is to be
at REST
the ball pushed comes
to rest after sometime
on its own
Dude , I don’t think
so.

5. GALILEO’S EXPERIMENT: DISPROVINGARISTOTLE‘S THEORY
Slant reduced
Slant zero =
• He performed a (thought)experiment in which he let a marble roll
down on 2 inclined planes( with little friction ) placed opposite to
each other.
• We can see that the ball travels all the way to the height from
which it was dropped
• If we reduce the slant of one of the inclined plane , then the
marble covers larger distance to reach the same height
• By following the same pattern , If we make the slant zero ( flat
) then the ball should travel forever to reach the same height
which meant that the natural state of an object is not to be at
rest

6. Galileocameupwiththeideathatobjects don’tstopbythemselvesbutan externalforce stopsthem
“ THENATURALSTATEOFAN OBJECTIS NOTTO BEATREST“
If Galileo’s experiment was
true , then why don’t we
see a moving marble going
forever ??
we don’t see moving objects
continue to move forever ,
because in most of the real life
situations friction acts on the
body and stops it

7. elaborated by
Newton in his
book
PRINCIPIA
Galileo’s idea , that objects
retain their
velocity unless an external
force is acted
Newton added that an Object in
motion ( with some velocity ) will retain its
velocity that is, it will continue to move .
Similarly an object in rest ( zero velocity )
will remain in rest until an external
unbalanced force is applied

8. INERTIA :
A OBJECT IN MOTION REMAINS IN MOTION
AN OBJECTIN REST REMAINS AT REST
In a qualitative way , we
can say that generally all
objects exhibit resistance
towards changing their state
of motion . this tendency of
objects is refered as
INERTIA

9. EXAMPLES OF INERTIA
When the bus is moving
and suddenly stops , we go
forward
When the bus suddenly
starts we go backwards
Inertia Of Motion Inertia of rest
Inertia of direction

10. Which Is heavier to kick?
spongeball Rock
Which is harder to
stop?
Toy car Real car
Empty
box Boxfull of books
Which is harder to
push?

11. Relation between Mass & Inertia
Does the
Sponge ball and
Rock have the
same Inertia ??
No,the
sponge ball
has less
inertia than
the rock
 We know that kicking a spongeball is
easier than rock !!
 Simlarly we know that stopping a car
is harder than a toy car !!
 Pushing a box full of books is harder
than an empty box !!
• All these examples suggest that the more massive an
object the more inertia it offers and vice versa
• This also implies that mass can help us in measuring
inertia
• Hence the mass of an object is the measure of
INERTIA

12. What exactly is force
??
• Force is either a push or pull is a vague definition which got
replaced by Newton’s second law which gives an accurate
definition of force and its relation with other quantities
• In the book Principia he stated his 2 nd law . The second law
of motion is the most important law ever in physics which
forms the core of kinematics
FORCE =

13. VELOCITY IS NOT ENOUGH!
oAccording to the 1st law , we know that an external
unbalanced force is required to change the state of
motion of a body
oTHE SECOND LAW DESCRIBES HOW ACCLERATION
OF AN OBJECT DEPENDS ON FORCE
oLets suppose , we kick each of the following balls of
different masses (m1-m5) with same amount of force –
‘F’
m1 m2
m3
m4 m5

14. Momentum :
 Eventhough , the force applied is same on all the
balls but the acceleration attained by each ball is
different , the larger the ball , the lesser
acceleration it attains and& vice - versa
 These observations suggest that the
impact produced by the object depends
on the velocity and mass
 Newton introduced a new quantity called
momemtum which relates mass & velocity
MOMENTUM = MASS * VELOCITY
P = MV

15. Newton’s 2nd law
• Newton stated that net external Force applied is directly
proportional to rate of change of momentum in the
direction of motion
• In a special case where ‘m’ is a constant.The 2nd law attains
a
a special form
F = MA
 The unitof force is kgms^2
or Newton (n)
Example of 2nd
law

16. Newton’s 3rd law:
• Newtons 3rd law states that every action has an equal and
opposite reaction
• These forces must act on the same body
• Note that both action and reaction happens simultaneously
• Walking can be explained by 3rd law , when we walk we push
the road , the road exerts a force to make us move forward

17. Examples of newtons 3rd law :

18. STAY CURIOUS !
Thank you