module 4 chpt 1 Energy and Its Uses

Module 4:
Gadgets Work Wonders (II)
Chapter 1 Energy And Its Uses
1© Copyright Star Publishing Pte Ltd

1.1 What are some common forms of
energy?
1.2 What is the Principle of the
Conversation of Energy?
1.3 What is power and how is it
calculated?

Objectives
 Show understanding that kinetic
energy, elastic potential energy,
gravitational potential energy,
chemical potential energy and thermal
energy are examples of different forms
of energy
 Show understanding that thermal
energy is transferred from a region of
higher temperature to a region of
lower temperature

What is Energy?
 Energy is the capacity to do work.
 There are many different forms of
energy. Three forms of energy that we
encounter in our daily lives are kinetic
energy, potential energy and thermal
energy.
© Copyright Star Publishing Pte Ltd 4

What is Kinetic energy?
 Kinetic energy is the energy which a moving
object has.
 A stationary object has no kinetic energy.
a stationary aeroplane has no
kinetic energy

Speed and kinetic energy
 An aeroplane has
more kinetic energy
when it is taking off
at high speed than
when it is moving
slowly on the taxiway
 A racing car has a lot
of kinetic energy
when it is moving at
high speed
 The faster an object moves, the more
kinetic energy it has.

What is Potential energy?
 Potential energy is stored energy.
 Three common forms of potential
energy are: elastic potential energy,
chemical potential energy and
gravitational potential energy.

What is Elastic Potential
Energy?
 Elastic potential
energy is stored in
objects which are
stretched, compressed
or bent.
(a) In archery, elastic
potential energy is
stored in a stretched
bow. When the bow is
released, the elastic
potential energy will be
used to push the arrow
forward at high speed.

Energy?
(b) When stretched or compressed, a
spring has elastic potential energy.
When the spring is allowed to return
to its original length, the elastic
potential energy will be released.

Energy?
(c) A trampoline makes use of elastic
potential energy to push a
person upwards.

What is Gravitational Potential Energy?
 Gravitational potential energy is the
energy that an object has because of its
position.
 The higher the position of an object, the
more gravitational potential energy it has.
(a) A flag has greater gravitational
potential energy after it is raised.
(b) A person has greater gravitational
potential energy after climbing to a
higher floor of a building.© Copyright Star Publishing Pte Ltd 11

What is chemical Potential Energy?
 Chemical potential energy is the energy
stored in substances such as fuels and
food.
(a) When food is digested, the chemical
potential energy in the food is released
to provide us with energy to live, work
and play.

Chemical Potential Energy
(b) Many households use liquid
petroleum gas (LPG) for cooking.
When burnt, the chemical potential
energy in the LPG is converted to
heat energy.

What is Thermal energy?
 Thermal energy is the energy an object has
because of its temperature.
 The hotter an object, the more thermal
energy it has.
 Our most important source of thermal energy
is the Sun.
 We obtain thermal energy for cooking and
keeping warm by burning fuels or using
electricity.

 Thermal energy travels from a region of
higher temperature to a region of lower
temperature.
 When there is no temperature difference,
there is no transfer of thermal energy.
thermal energy is used
for cooking)

 When a bottle of hot milk is placed in a
bowl of cold water, thermal energy
moves from the hot milk to the cold
water. This causes the milk to cool
down and the water to warm up.

Thermal energy is transferred from a hotter
region to a cooler region.
 The handle of a heated
pan feels warm
 The handle of a metal
spoon in hot tea feels
warm
Activity Book Link
Activity 1.1
Transfer of Thermal Energy
Activity 1.2
Temperature Change

energy?
calculated?

Objectives
 Show understanding that kinetic
energy, elastic potential energy,
gravitational potential energy,
chemical potential energy and thermal
energy are examples of different forms
of energy
 Show understanding that thermal
energy is transferred from a region of
higher temperature to a region of
lower temperature

The Principle of the Conservation of
Energy
 The Principle of the Conservation of Energy
states that:
(a) energy cannot be created or destroyed,
(b) energy can only be changed from one
form to another or transferred from one
object to another.
 When an energy conversion occurs, the total
energy before and after the conversion is the
same.

Examples of energy
conversion
 Some examples of energy conversion
are:
(a) Throwing a ball vertically upwards
(b) Shooting an arrow with a bow
(c) Lighting a bulb with a battery

Throwing a ball vertically upwards
 At A, the ball
has maximum
kinetic energy.
 As the ball
moves upwards,
the kinetic
energy is
converted to
gravitational
potential
energy
 When the ball
reaches the highest
point B, all the
kinetic energy has
been converted to
gravitational
potential energy.
 As the ball falls
downwards from B,
its gravitational
potential energy is
converted to kinetic
energy

Shooting an arrow with a bow
 When an archer
releases the bow,
the elastic
potential energy
stored in the
stretched bow is
converted to
kinetic energy of
the arrow.
archer releasing
an arrow

Lighting a bulb with a battery

Charging mobile devices
Activity Book Link
Activity 1.3
Forms of Energy

Importance of Conserving Energy
 When we boil a kettle
of water, chemical
energy in the gas is
converted to heat
energy.
 Some of these energy
conversions are very
hard to reverse.
 We should reduce
the amount of
energy used.
we should turn off the gas once the
water starts boiling

Importance of Conserving Energy
 We depend
heavily on
electrical energy in
our modern living.
 We reduce the
amount of fossil
fuels used when
we reduce the
use of electrical
energy.
In Singapore, solar energy is a possible
source of energy we can tap on

How can we conserve energy?
 We can reduce
the amount of
fuels used by
taking public
transport.
 We can use
renewable
sources of
energy such as
wind and solar
energy. © Copyright Star Publishing Pte Ltd 28
wind energy is only suitable for
places with strong winds

How can we conserve
energy?
 Buildings can be
designed to be
energy efficient
and to reduce need
for air-
conditioning.
 Other buildings
make use of
natural light to
reduce the need for
electric lighting.
the National Library building is an
internationally acclaimed ‘green’
building.

energy?
calculated?

Objectives
 Relate power to energy transferred
and time taken, using appropriate
examples and the equation
power = in simple systems
time
energy

What is Power?
 Power is the rate of energy
conversion.
Hakkim is said to have more power than Ben since
he gains the same amount of gravitational potential
energy in a shorter time.

Formula for Power
 Power can be calculated using the
formula:
power =
where P = Power (in W)
E = Energy converted (in J)
t = time taken (in s)
 The SI unit of power is the watt (W).
time
energy

Formula for Energy
 To calculate energy, the formula can
be rewritten as:
energy = power × time
 The SI unit of energy is the joule (J).

Example
 The amount of energy needed for
Hakkim to climb up a ladder is 1200 J.
If he can complete the climb in 10 s,
calculate the power.
power =
time
energy
=
10s
1200J
= 120 W
Activity Book Link
Activity 1.5
Heating up My Cup
of Tea

module 4 chpt 1 Energy and Its Uses

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