FORM 2 CHAPTER 8 FORCE AN MOTION

CHAPTER 8
FORCE AND MOTION

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Content

1.Force
2.Measuring Force
3.Application of Frictional Force 7.4
Application of the Concept of Work 7.5
Application of the Concept of Power 7.6
The Importance of Force in Daily Life

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What is force ?

• Push and pull upon an object.

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ALMOST EVERY ACTIVITY THAT WE DO IN OUR
DAILY LIFE USES FORCE.

CAN YOU NAME IT?





Types of forces

1. Frictional force
2. Gravitational force
3. Normal force
4. Buoyant force
5. Weight
6. Elastic force

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1.Frictional force

• The force that resists the movement
between two surfaces that are in contact
with each other.

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2. Gravitational force

• The force of attraction that causes objects
to falls towards the Earth.

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3.Buoyant force

• The thrust force acting on an object that
is floating on the surface of a fluid.
• Liquid @ gas

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4.Elastic force

• Exist when a material is stretched or
compressed.

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5.The weight

• The weight of an object is defined as the
gravitational force acting on the object.

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6.Normal force

• The force produced when an object is in
contact with surface.

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Types of forces DEFINITION

Normal force
Elastic force
Buoyant force
Frictional force
Gravitational force
Weight



Characteristic of Force

A force can be measured using a
spring balance.

• The unit of force is Newton (N).

1kg(mass) = 10N (weight)
10k g =100N
100g = 1N



Measuring Force

• THE S.I UNIT FOR FORCE IS NEWTON (N)
• The weight of an object is the gravitational force acting on the
object.
• On Earth, an object with a mass of 100 g has a weight of 1 N.
• Therefore, an object with a mass
of 1 kg has a weight of 10 N.

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Weight Vs Gravity

• The weight of an object depends on the pull
of gravity

• The force of gravity on the moon is only one-
sixth of the force of gravity on earth

• Thus, the same object will have different
weight on earth and the moon

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Action-reaction Pair

• Newton’s Third Law states that :
every action force, there is a reaction force of the
same magnitude but in the opposite direction.

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Weight and mass

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8.2 EFFECT OF FORCE

The effects of a force include:
a) force changes the shape of an object.
b) force changes the position of an object.
c) force changes the speed of a moving object.
d) force changes the direction of a moving object.
E) force changes the size of an object
f) force can moves a stationary object.



Buoyant Force

1.Meaning:The thrust force acting on an object that is
floating on the surface of a fluid.
2. Actual weight: weight of an object in the air
3.Apparent weight: weight of an object immersed in fluid
Buoyant force = actual weight – apparent weight



Buoyant Force

1. An object will float on water if the buoyant force acts
on it is enough to support its weight.

2. Buoyant force is a force that acts on the object when
the object completely submerged in water.

Activity 8.4 textbook page 177

The concept of density

Density and buoyant effect



LEVER

1.A lever is a bar that rotates on a fixed

point.

2.A lever is a simple machine.
3.A lever allows us to use minimal force

to do work.

Purpose of a lever:

1. A lever allows us to do work easily.
2. A lever allows us to use minimal force to do work.

Classes of lever

Classes of lever

In the middle of the lever 

F - first class lever
L - second class lever
E - third class lever

First Class Lever

• In a first class lever , the Fulcrum is between the effort
and the load.

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Second class lever

• In a and the effort. second lever , the Load is between the
fulcrum

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Third Class Lever

• In a third class lever , the Effort is between the fulcrum
and the load.

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Moment of force

1. The moment of force is the turning effect of force

on an object.

2. Formula:

Moment of force = Force (N) x perpendicular
distance to the force (m).

3. The moment of force increase if:
a) Magnitude of force increases.
b) perpendicular distance from pivot (fulcrum) to
effort increases.

Moment of force in daily life