This chapter discusses Newton's laws of motion and their applications. Students are expected to learn about the different types of forces acting on objects like weight, tension, normal force, and friction. They should be able to draw free body diagrams showing all the forces and determine the net or resultant force. The chapter also covers Newton's three laws of motion - the law of inertia, the second law relating force and acceleration, and the third law of action and reaction. Examples are provided to illustrate applications of these laws to situations like motion in lifts and objects on horizontal surfaces.

1. CHAPTER 3:
NEWTON’S LAW OF
MOTION AND ITS
APPLICATIONS

2. 2
Learning Outcome:
At the end of this chapter, students should be able to:
 Identify the forces acting on a body in different situations:
◦ Weight
◦ Tension
◦ Normal Force
◦ Friction
 Draw free body diagram.
 Determine the resultant force.
3.1 INTRODUCTION

3. 3
• is defined as something capable of changing state of motion or size or dimension
of a body.
• There are 4 types of fundamental forces in nature:
a) Gravitational forces
b) Electromagnetive forces
c) Strong nucleur forces
d) weak nucleur forces
3.1.1 Basic of Forces & Free body diagram
• Since force has magnitude and direction, it is a vector quantity
• If several forces acts simultaneously on the same object, it is
the net force that determines the motion of the object.
• The net force is the vector sum of all the forces acting on the object
and it is often called resultant force.
The magnitude of a force can
be measured using a spring
scale.

4. Examples of applied forces

5. 5
• It always directed toward the centre of the earth or in
the same direction of acceleration due to gravity, g.
g
m
W



Weight (Force),
• Weight is defined as the force with which a body is attracted
towards the center of the earth.
• It is dependant on where it is measured, because the
value of g varies at different localities on the earth’s
surface.
• It is a vector quantity.
Equation:
• The S.I. unit is kg m s-2 or Newton (N).
W


6. 6
W
All the W pointing downward as shown in figure 3.1.1 above
Figure 3.1.1

7. 7
Tension,
• Tension is the magnitude of the pulling force that is directed
away from the object and attempts to stretch & elongate
the object. (figure 3.1.2)
• Measured in Newton and is always parallel to the string on
which it applies.
Single string system:
T
T
T
m1 m1 m1
ϴ
Figure 3.1.2

8. 8
T T
T
T
m1
Single string system (smooth pulley)
Multiple string system
m1 m2
T2
T2 T3 T3
The tension T acts for the whole
one string but it will be different
if it acts on different masses, T1
and T2 as shown in fig 3.1.3 and
Fig 3.1.4
Fig 3.1.3
Fig 3.1.4
T1

9. 9
m4
m1
m2
m3
T3
T1 T1
T1
T1
T2 T2
T2
T2
T3 T3
T3
Multiple string system (inclined plane)
The are three different tension T1, T2 and T3
acts on different masses of m1, m2 and m3
as shown in fig 3.1.5.
Fig 3.1.5

10. 10
N1
N2
N3
m1
m2
m3
Surface 1
Surface 2
Surface 3
Normal Force (Reaction Force), N or R
is the contact force component , which is perpendicular to the surface
of contact and exerted on an object by preventing the object from
penetrating the surface. (fig 3.1.6)
Fig 3.1.6

11. Frictional force,
11
N
f 

force
frictional
:
f
friction
of
t
coefficien
:
μ
where
• is defined as a force that resists the motion of one surface
relative to another with which it is in contact.
• is independent of the area of contact between the two surfaces
• is directly proportional to the reaction force.
f


12. 12
Figure 3.1.7
N
fs
W
F
N
W
F
N
W
F
fs = max fk
Block at rest Block about to slide Block is sliding
There are three different stages of friction acts on a block
which are going to slide as shown in figure 3.1.7.

13. Free Body Diagram
13
• is defined as a diagram showing the chosen body by
itself, with vectors drawn to show the magnitude &
directions of all the forces applied to the body by the other
bodies that interact with it.
• A single point may represent the object.
Example : Sketch free body diagrams for each case
Case 1 : Horizontal surface
a) An object lies at rest on a flat horizontal surface
m

14. F
b) A box is pulled along a rough horizontal surface by a
horizontal force, F
m
a
Case 2 : Inclined Plane
A box is pulled up along a rough inclined plane by a force, F
m

15. 15
Case 3 : Hanging object
An object is hang by using a light string
m
m

16. 16
Case 4 : Pulley
m1
m2
m2
m1

17. Learning Outcome:
At the end of this chapter, students should be able to:
 State Newton’s First Law
 Define mass as a measure of inertia.
 Define the equilibrium of a particle.
 Apply Newton’s First Law in equilibrium of forces.
 State and apply Newton’s Second Law.
 State and apply Newton’s Third Law.
17
3.2 Newton's Law of Motion

18. 3.2 Newton’s laws of motion
states “an object at rest will remain at rest, or continues
to move with uniform velocity in a straight line unless it
is acted upon by a external forces”
18
Inertia
is defined as the tendency of an object to resist any change
in its state of rest or motion.
is a scalar quantity.
Newton’s first law of motion
The first law gives the idea of inertia.
0


 F
Fnett

19. • Figures 3.2 show the example of real experience of inertia.
19
Figure 3.2
Equilibrium of object / particle
The resultant of forces is zero. (Translational equilibrium)
Equilibrium of object / particle occurs when the net force
exerted on it is zero.
Newton’s 1st law of motion
0

F

20. interval
time
:
dt
20
its can be represented by
where force
resultant
:
F

State and apply Newton’s Second Law.
states “the rate of change of linear momentum of a moving body
is proportional to the resultant force and is in the same direction
as the force acting on it”
dp : Change in momentum
dt
dp
F 


21. If the forces act on an object and the object moving at
uniform acceleration (not at rest or not in the equilibrium)
hence
21
Newton’s 2nd law of motion restates that “The acceleration of an
object is directly proportional to the nett force acting on it and
inversely proportional to its mass”.
One newton(1 N) is defined as the amount of nett force that
gives an acceleration of one metre per second squared to a
body with a mass of one kilogramme. 1 N = 1 kg m s-2
is a nett force or effective force or resultant force.
The force which causes the motion of an object.
F

m
F
a

 

ma
F
Fnett 




22. Newton’s third law of motion
22
For example :
When the student push on the wall it will push back with
the same force. (refer to Figure 3.2.1)
A (hand)
B (wall)
Figure 3.2.1
is a force by the hand on the wall (action)
Where
is a force by the wall on the hand (reaction)
states “every action force has a reaction force that is equal in
magnitude but opposite in direction”.
BA
AB F
F




AB
F

BA
F


23. 23
A rocket moves forward as a result of the push exerted on it
by the exhaust gases which the rocket has pushed out.
Figure 3.2.2
Force by the book on the table (action)
Force by the table on the book (reaction)
When a book is placed on the table. (refer to Figure 3.2.2)
If a car is accelerating forward, it is because its tyres are pushing
backward on the road and the road is pushing forward on the tyres.
In all cases when two bodies interact, the action and reaction
forces act on different bodies.

24. 24
The motion of an elevator can give rise to the sensation
of being heavier or lighter.
Apparent weight
The force exerted on our feet by the floor of the elevator.
If this force is greater than our weight, we felt heavier, if
less than our weight , we felt lighter.

25. Case 1 : Motion of a lift
 Consider a person standing inside a lift as shown in
Figures 3.2.7a, 3.2.7b and 3.2.7c.
a. Lift moving upward at a uniform velocity
25
Since the lift moving at a
uniform velocity, thus
Therefore
Figure 3.2.7a mg
N
mg
N
Fy





0
0
N

26. b. Lift moving upwards at a constant acceleration, a
26
By applying the newton’s 2nd
law of motion, thus
Figure 3.2.7b
)
( g
a
m
N
ma
mg
N
ma
F y
y







27. c. Lift moving downwards at a constant acceleration, a
27
By applying the newton’s 2nd
law of motion, thus
Figure 3.2.7c
 Caution : N is also known as apparent weight and
W is true weight.
)
( a
g
m
N
ma
N
mg
ma
F y
y






mg
W 

28. Case 2 : An object on Horizontal surface
 Consider a box of mass m is pulled along a horizontal
surface by a horizontal force, F as shown in Figure 3.2.8
28
Figure 3.2.8
 
 ma
F
F nett
x ma
f
F 

  0
y
F mg
N 
x-component :
y-component :
mg
N

29. 1)
2)
3)
4)
5)
prepared by NASS
Rules/Law of Indices
n
m
n
m
a
a
a 

  mn
n
m
a
a 
n
m
n
m
a
a
a 

  0
, 
 b
b
a
ab m
m
m
0
, 







b
b
a
b
a
m
m
m
0
;
1



a
a
a n
n
6)
0
a
;
1
a0


7)
8)
0
a
;
a
a n m
n
m

