Lss module 1 chpt 1 investigating forces

MODULE 1:
GADGETS WORK WONDERS (I)
Chapter 1 Exploring Forces
1© Copyright Star Publishing Pte Ltd

1.1 What are the effects of forces?
1.2 How can forces be measured?
1.3 What are the effects of friction?
1.4 How do simple machines work?

Objectives
 State that a force can change the shape,
size, state of rest and motion of a body
 Give examples of different forces:
pushing, lifting, stretching, twisting,
pressing, gravitational, frictional and
magnetic forces
 Infer the effects of forces such as
◦ change in state of rest and / or motion of a
body
◦ change in shape and / or size of a body 3© Copyright Star Publishing Pte Ltd

What is a force?
 A force is a push or
a pull.
 Actions such as
lifting, stretching,
bending, twisting
and squeezing
involve pushing and
pulling.
Actions Involving PushingActivity Book Link
Activity 1.1
Forces in Daily Life

© Copyright Star Publishing Pte Ltd 5
Actions Involving Pulling

Actions Involving Pushing and Pulling

Other examples of forces
 Other examples of
forces are
frictional force,
magnetic force
and gravitational
force.
How is life in space without any
gravitational pull?

What is frictional force?
 Friction is the
force that acts
between two
surfaces in
contact.
 When we hold a
glass of water,
there is friction
between our hand
and the glass.

What is magnetic force?
 A magnetic force
is the force
between two
magnetic poles.
 It can be an
attractive or a
repulsive force.
Magnetic forces are useful in
many areas of our lives.

What is gravitational force?
 Gravitational
force is the force
that pulls an
object towards the
earth.
Gravitational force helps in daily tasks
such as pouring water from a jar.

What are the effects of forces?
 A force can
change the shape
and/or size of an
object.
crushing a tin can changes its
shape and size
squeezing a sponge can changes its
shape and size

What are the effects of forces?
 A force can change the motion of an object;
 for example,
(i) move a stationary object,
(ii) stop a moving object,
(iii) change the speed of a moving object,
(iv) change the direction of a moving object.

a force can cause a stationary ball to move
a force can make a moving ball roll faster
or slower
a force can cause a ball to change direction

Objectives
 Use a spring balance to measure
force
 Use newton as the unit of force

How are Forces Measured?
 Forces are
measured using
spring balances.
 The International
System of Units
(SI unit) of force
is the newton (N).
an extension
spring balance

Spring balances
 The two types of spring
balance are:
(a) extension spring
balance
(b) compression spring
balance
 In an extension spring
balance, the force causes
the spring to become
extended or longer.
 In a compression spring
balance, the force causes
the spring to be compressed
or become shorter.
is the force exerted by the food on
the compression spring balance a
push or a pull?

How do we read a spring balance?
 The size of the force can be read from the
scale of a spring balance.
 The reading on the scale shown is 50 N.

What is weight?
 Weight is the force
of gravity pulling an
object towards the
Earth.
 Weight is not the
same as mass.
an electronic balance is used
to measure mass
Activity Book Link
Activity 1.2
Making a Spring Balance
Activity 1.3
Measuring Forces

Differences between weight and mass

Objectives
 Describe the effects of friction on the
motion of an object

What is Frictional Force?
 Friction is a force which opposes motion.
 It acts between two surfaces in contact.
friction causes a rolling ball to slow down and stop

What are the Factors Affecting Friction?
 Friction depends
on:
(a) the
smoothness of the
two surfaces in
contact.
(b) the force
pressing the two
surfaces together.
a carrom seed moves easily across a
smooth carrom board
a heavy box on the right experiences a
larger friction than an empty one

Does the Surface Area in Contact Affect
Friction?
 Friction does not depend on the surface area in
contact.
 A rectangular block experiences the same amount
of friction no matter which side it is placed on a
surface.
Activity Book Link
Activity 1.5
Friction and Area in Contact

Is Friction a Useful Force?
 Friction helps us to walk without slipping.
 Friction is needed for braking.
 Friction helps us to grip things
walking on smooth ice
can make you fall brake pads on a bicycle help it
to slow down and stop
friction helps a person
to grip a pencil

Is Friction a Nuisance?
 Friction can also be a nuisance as it produces
unwanted heat in machines and causes wear
and tear.
 Friction can be reduced by:
(a) Using lubricants
(b) Using ball bearings
lubricants and ball bearings reduce friction between moving parts of machines

Objectives
 Identify the different types of simple
machines (levers, inclined planes and
pulleys) and give everyday examples of
their use
 Investigate the effort used when the
following is used to raise a load
▲ Lever
▲ Inclined plane
▲ Pulley

How do Simple Machines Help Us do Work?
 A simple machine is a
device that makes
work easier for us. It
can:
(a) reduce the force
needed to move a
load,
(b) change a small
movement into a large
one,
(c) change the
examples of simple machines

Types of simple machines
 Three common
types of simple
machines are:
(a) levers,
(b) inclined planes,
(c) pulleys.
a screwdriver acts as a lever to help
open a tin of paint

Lever system
 There are three parts in a lever system:
(a) the fulcrum (b) the effort (c) the
load.

Why is it easier to open a tin of paint with
a long screwdriver than a short one?
 The further the
effort from the
fulcrum, the
smaller the effort
needed to move
the load.

Classes of levers
 There are three
classes of levers:
◦ 1st class lever
(Fulcrum is between
load and effort)
◦ 2nd class lever
(Load is between
effort and fulcrum)
◦ 3rd class lever
(Effort is between
load and fulcrum)
1st class lever
2nd class lever
3rd class lever

Examples of the three classes of levers

How do levers make work easier?
 First and second class levers make
work easier by allowing us to use a
small effort to overcome a large load.
 Third class levers enable a small
movement of the effort to result in a
large movement of the load.
 This makes work such as sweeping the
floor faster. However, an effort larger
than the load is needed.

What is an inclined plane?
 An inclined plane is a flat surface with one
end higher than the other.
a wheelchair ramp is an
example of inclined plane
worker moving goods up an
inclined plane into a truck

How does an inclined plane make
work easier?
 Moving a load up an
inclined plane
requires a smaller
effort than lifting the
load vertically.
 However, the load
has to be moved
over a longer
distance along the
inclined plane.
Activity Book Link
Activity 1.7
Inclined Planes

What is a Pulley?
 A pulley is a wheel with a
groove for holding a rope
or a cable in place.
 In a single fixed pulley
system, the effort needed
is equal to the load.
However, it is still
considered a simple
machine because it
makes work easier.
 Pulleys are also used in
construction cranes,
cable cars, window
blinds and yachts (to
raise sails).
a flag pole uses a pulley
Activity Book Link
Activity 1.8 Pulley Systems

Useful applications of pulleys
construction crane
cable car
window blinds
yacht

Lss module 1 chpt 1 investigating forces

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