A presentation on all the laws of motion including Law of Conservation Of momentum with applications and mathematical equations.

2. Acknowledgement
• We would like to give our sincere thanks to Mrs.
Swarachita Hazra, our science teacher for giving
such an informative project. It was real fun to
have learnt through this project instead of
routine text books. We gained a lot of knowledge
while surfing through internet. We hope we will
get such projects in the future also. Thank You
once again.

3. ISAAC NEWTON
• Sir Isaac Newton was an
English physicist and mathe
matician who is widely
regarded as one of the
most influential scientists
of all time and as a key
figure in the scientific
revolution. Newton also
made seminal
contributions to optics and
shares credit with Gottfried
Leibniz for the invention of
the infinitesimal calculus.
He gave 3 laws of motion.
Here, in this presentation
we will learn about them.

4. Force
• Force is a push or a pull acting on an object.
Its SI unit is Newton i.e: Kg m/sec2
Its Formula is Mass x Acceleration
Later in the presentation we will learn how
he formula is derived.
Forces are of two types
1)Balanced Force
2)Unbalanced Force

5. BALANCED FORCE
IF THE RESULTANT OF ALL THE FORCES
ACTING ON A BODY IS ZERO,THE FORCES
ARE CALLED BALANCED FORCE

6. UNBALANCED FORCE
IF THE RESULTANT OF ALL THE FORCES
ACTING ON A BODY IS NOT ZERO,THE
FORCES ARE CALLED UNBALANCED
FORCE

8. INERTIA
• Inertia is the property of matter that cause it
to resist any change in its motion or state of
rest
• INERTIA makes the moving object continue
to move at a constant speed in the same
direction unless some external force changes
the object’s motion
• Inertia is not physical quantity and thus it
does not have units

9. Introduction to Newton's First Law of
Motion
• Some of the bodies (or objects) around us are
at rest , whereas other are in motion.
Newton's first law describes the behavior of
such bodies which are in a state of rest or of
uniform motion in a straight line.

10. Newton’s first law of motion
• According to Newton's first law...
• An object at rest will remain at rest or an
object in motion will remain in motion in a
straight line at constant speed , unless an
external force is applied to it & changes its
state of motion.

11. Activity 1
• Make a pile of similar carom coins on a table as shown in
the figure.
• Attempt a sharp horizontal hit at the bottom of a pile
using a striker. If the hit was strong enough, the bottom
coin moves out quickly. Once the lowest coin is
removed, the inertia of the other coins make them ‘fall’
vertically on the table.

12. Activity 2
• Set a 5 rupee coin on a stiff card covering an empty glass
tumbler as shown in the figure.
• Give the card a sharp horizontal flick with a finger. If we
do it fast then the card shoots away, allowing the coin to
fall vertically into the glass tumbler due to its inertia.
• The inertia of the coin tries to maintain its state of rest
even when the card flows off.

14. Usain Bolt made a world record of running 100m in
just 9.58 secs. But why does he and the other athletes
run after finishing the race?
•

15. This is because
• An athlete keeps on running few meters after
finishing line because initially both the upper
and the lower part of the body of the athlete
are in state of motion. If he reaches the
finishing line and stops then his legs come to
rest but hut the upper part of the body tends
to remain in the state of motion due of
inertia of motion and he falls forward so, in
order to avoid any injury he keeps on running
for few meters after the finishing line..

16. A bullet is fired from a gun and a hole is made in the
object. But why does this happen?

17. This is because
• When we fire a bullet from a gun to
stationary objects, a hole is made in them
because initially both bullet and the objects
are in the state of rest. When bullet is
fired, the bullet comes to motion but the
object tends to remain in the state of rest
due to inertia of rest and hence a hole is
made.

19. MOMENTUM
• If an object is to be accelerated, we know that a
greater force is required to give a greater
velocity. So, there appears to exist some
quantity of importance that combines the
object’s mass and its velocity.
• One such property called momentum was
introduced by Newton. The momentum, p of an
object is defined as the product of its mass, m
and velocity, v.
• That is,
p = mv

20. • Momentum has both direction and magnitude.
• Its direction is same as that of velocity, v.
• The SI unit of momentum is kilogram-metre per
second (kg m s-1).
• Since the application of an unbalanced force brings a
change in the velocity of an object, it is therefore clear
that a force also produces a change in momentum.
• The change of momentum of the car is not only
determined by the magnitude of the force but also by
the time during which the force is exerted.
• The force necessary to change the momentum of an
object depends on the time rate at which the
momentum is changed.

21. Newton’s 2nd Law of Motion
• Second law of motion states that rate of change of
momentum is directly proportional to the force applied.
• For e.g.- During the game of tennis if the ball hits a player it
does not hurt him.
• On the other hand, when a fast moving cricket ball hits a
spectator , it may hurt him.

22. Mathematical Representation
• Change of momentum= mv-mu
Rate of change of momentum= mv-mu/t
mv-mu/t ∝ F
m(v-u/t) ∝ F
kma = F
Where k stands for constant of proportionality
F=MA

23. Understand the First law of Motion
• Let us consider a situation
in which a car with a dead
battery is to be pushed
along a straight road to
give it a speed of 1m s-
1, which is sufficient to start
its engine. If one or two
persons give a sudden push
to it, t hardly starts. But a
continuous push over
sometime results in a
gradual acceleration of the
car to this speed.

24. Activity 3
• Take a rubber balloon & inflate it fully. Tie its neck using a
thread & fix a straw on its surface.
• Pass the thread through the straw & fix one end on a wall.
• Fix the other end on a wall at some distance as shown
below.
• Now remove the thread tied on the balloon & let the air
escape.
• Observe the direction in
which the straw moves.

25. Activity 4
• Take a test tube & put a small amount of water on it.
Place a stop cork at the mouth of it.
• Now suspend the test tube horizontally by two strings or
wires as shown in the figure.
• Heat the test tube with a burner until water vaporises and
the cork blows out.
• Observe that the test
tube recoils in the
direction opposite to
the direction of the cork.

27. Why the fielder lowers his hand to take the catch?

28. This is because
• A fielder lowers his hands while taking a
catch. He does so to increase the time of
momentum in which the momentum is
reduced to zero. Hence the player feels less
force on his hands according to Newton’s 2nd
Law.

29. Why does they wear boxing gloves while boxing?

30. This is because
• Boxers wear boxing gloves to increase the
time of impulse in which the momentum is
reduced to 0 according to Newton’s 2nd law
and the boxer gets less hurt when the other
one punches him.

32. The third law of motion says that for every
action there is an equal and opposite
reaction.
This must be remembered that action and
reaction always act on two different objects.
Newton’s 3rd Law of Motion

33. Understand the 3rd Law of motion

34. Action-Reaction Pair
• Action: the tires on a car push on the road…
Reaction: the road pushes on the tires.
• Action: while swimming, we push the water
backwards...
Reaction: the water pushes us forward.
• Action: a rocket pushes out exhaust…
Reaction: the exhaust pushes the rocket forward.

35. Activity 5
• Request two children to stand on two separate carts as
shown in the figure.
• Give them a bag full of sand and ask them to play a game
of catch with the bag.
• Does each of them receive an instantaneous reaction as a
result of throwing the sand bag ?
• You can paint a white line on
cartwheels to observe the
motion of the two carts when
the children throw the bag
towards each other.

38. This is because
A swimmer is able to swim due to Newton’s
3rd Law of Motion. He pushes the water
backward with his hands and water in turn
pushes him with equal and opposite force
in forward direction.

39. The A4 (Aggregat 4) rocket was the first rocket to be
launched. It was developed in Germany during the
second World War. But how does a rocket works?

40. This is because
• Rockets work on Newton’s 3rd law. When fuel
in the rocket burns, the gases rush down.
These gases exert a force on the ground and
ground exerts equal and opposite force on
the rocket and the rocket propels.

42. LAW OF CONSERVATION
OF MOMENTUM
• The Law of Conservation of Momentum
states that if two bodies collide with
each other, the total momentum before
and after collision remains conserved.

43. Mathematical Representation
Total Momenta before collision = Total Momenta after collision
m1u1+ m2u2 = m1v1 = m2v2

45. Solution:
We have been given that u= 3 m s-1 and v= 7 m s-1 , t= 2 s and m= 5 kg.
From Eq. we have,
F = m(v-u)
t
Substitution of values in this relation gives
F = 5 kg (7 m s-1 – 3 m s-1 )/ 2s= 10N
Now, if this force is applied for a duration of 5 s( t= 5 s), then the final
velocity can be calculated by rewriting Eq. (9.5) as
v = u + Ft
m

46. On substituting the values of u, F, m and t, we
get the final velocity,
v = 13 m s-1

47. 5
10
15
20
25
1 2 3 4 5 6 7 8 9 10 11 12

48. Solution:
The initial velocity of the ball is 20 cm s-1 . Due to
the friction force exerted by the table, the
velocity of the ball decreases down to zero in 10
s. Thus, u= 20 cm s-1 ; v= 0 cm s-1 and t= 10 s.
Since the velocity- time graph is a straight line, it
is clear that the ball moves with a constant
acceleration. The acceleration a is
a = v-u
t
= (0 cm s-1 – 20 cm s-1 )/ 10 s
= -2 cm s-2 = -0.02 m s-2

50. Solution:
We have the mass of bullet, m1 = 20 g (= 0.02 kg) and the mass of the
pistol, m2 = 2 kg; initial velocities of the bullet (u1 ) and pistol (u2 ) =
0, respectively. The final velocity of the bullet, v1 = 150 m s-1 . The
direction of bullet is taken from left to right ( positive, by
convention, Fig. 9.17). Let v be the recoil velocity of the pistol.
Total momenta of the pistol and bullet before the fire, when the gun is
at rest
= (2+ 0.02) kg X 0 m s-1
= 0 kg ms-1
Total momenta of the pistol and bullet after it is fired
= 0.02 kg X (+ 150 m s-1 ) + 2 kg X v m s-1
= (3 + 2v) kg m s-1 .
Cont. in the next slide.

51. According to the law of conversation of
momentum
Total momenta after the fire = Total momenta
before the fire
3 + 2v = 0
 v = -1.5 m s-1 .
Negative sign indicates that the direction in
which the pistol would recoil is opposite to
that of bullet, that is, right to left.

52. Summary• First law of motion : An object continues to be in a state of rest or
of uniform motion along a straight line unless acted upon by an
unbalanced force .
• The natural tendency of objects to resist a change in their state of
rest or uniform motion is called inertia .
• The mass of an object is a measure of its inertia . Its SI unit is kg .
• Force of friction always opposes motion of objects .
• Second law of motion : The rate of change of momentum of an
object is proportional to the applied unbalanced force in the
direction of the force .
• The SI unit of force is kg m/s2 . This is also known as Newton and
represented by the symbol N . A force of 1 Newton produces an
acceleration of 1m/s2 on an object of mass 1 kg .
• The momentum of an object is the product of its mass and
velocity and has the same direction as that of the velocity . Its SI
unit is kg m/s
• Third law of motion : To every action , there is an equal and
opposite reaction and they act on 2 different bodies .
• In an isolated system (where there is no external force ) , the total
momentum remains conserved .
s2

53. Made by :Group 2(Roll No. 11-20)
Group Leader: Samyak Jain