Lss module 1 chpt 3 investigating heat

MODULE 1:
GADGETS WORK WONDERS (I)
Chapter 3 Investigating Heat
1© Copyright Star Publishing Pte Ltd

3.1 What is temperature and how is it
measured?
3.2 What is heat and why is it
important?
3.3 Why can expansion and contraction
be both useful and harmful?

Objectives
 Understand that temperature is a
measure of the degree of hotness and
coldness of an object
 Recognise that there are different
types of thermometers (digital
thermometer, laboratory thermometer
and temperature sensors)
 Measure temperature using a
thermometer or a datalogger with
temperature sensors

Temperature
 Temperature is a
measure of the degree
of hotness or coldness
of an object.
 In Singapore,
temperature is usually
measured in degree
Celsius (°C).
 We use a thermometer
to measure temperature
reliably and safely.
using our sense of touch
to determine temperature may
not be accurate

Thermometers –
Liquid-In-Glass Thermometers
 The liquid-in-glass thermometer consists of a round glass
bulb which contains liquid and a narrow glass tube.
 The stem of the thermometer is marked with a scale.
 Alcohol and mercury are used in this type of thermometer.
 For daily uses, alcohol is preferred as it is safer than
mercury which is poisonous.
© Copyright Star Publishing Pte Ltd 5
a liquid-in-glass laboratory thermometer

How does a Liquid-In-Glass
Thermometer work?
 When the thermometer is placed in a hot place, the liquid in
the bulb will expand and move up the narrow tube.
 The opposite happens when the thermometer is placed in a
cold place. The liquid will contract and move down the
narrow tube.
 The position where the liquid stops indicates the
temperature which can be read from the scale.

Digital Thermometers
 Digital thermometers do not use liquids to measure
temperature. Instead of reading the temperature from a
scale, the temperature is displayed directly.
 Three common types of digital thermometers are:
(a) digital oral thermometer
(b) infrared ear thermometer
(c) infrared non-contact thermometer
a digital oral thermometer

Digital thermometers
Infrared ear
thermometer
Infrared non-contact
thermometer

Dataloggers
 A datalogger with a
temperature sensor is
used to keep track of
temperature over a
period of time.
 The datalogger measures
and records the
temperature at preset
intervals over a period of
time.
datalogger with
temperature sensor
Activity Book Link
Activity 3.1
How Hot is the Water?
Activity 3.2
Hot and Cold Log

measured?
important?
3.3 Why can expansion and contraction
be both useful and harmful?

Objectives
 Explain that heat is a form of energy
that flows from a hotter to a colder
region
 Recognise that when the temperature
of a substance increases, the
substance has absorbed heat; when
the temperature of a substance
decreases, the substance has lost
heat
 State the importance of heat energy in

What is Heat Energy?
 Heat is a form of energy that flows from a hotter to a
colder region.
 In the diagram on the left, the hotter block will become
cooler while the cooler block will become hotter until both
blocks have the same temperature.
two iron blocks at different
temperatures
two iron blocks at different
temperatures

What is Temperature?
 Temperature is the measure of the degree of hotness of an
object.
 Temperature tells us how hot or cold an object is.
 The amount of heat energy an object has depends on both its
mass and temperature.
 The higher the temperature of an object, the more heat it has.
the water in Beaker B has more heat energy as its mass is greater

Temperature change
 When an object gains heat, its temperature will increase. On the
other hand, when the object loses heat, its temperature will
decrease.
 However, there will be no change in temperature when a
substance is changing its state (e.g. Melting or boiling), even
when heat is gained or lost.
when the water in the pot
gains heat, its temperature
increases
when the cans of drink lose heat,
their temperature decreases

Importance of Heat Energy
 Heat is important to
us.
(a) Heat is used to
cook our food,
making it safe to eat.
(b) In cold countries,
heat is used to keep
homes warm during
winter.
a fireplace provides warmth from
burning wood

(c) Heat is used to dry things quickly.
(d) Heat is used to kill germs.
clothes dry quickly
under the sun
sterilising baby milk
bottles with steam

(e) Heat is needed in industrial processes. During welding,
heat is used to melt two pieces of metal. When they
have cooled down, the two pieces of metal will be joined
together strongly.
(f) Heat is used to refine metals.
welding of metal
makes use of heat
metal rods being refined
in a huge burner
Activity Book Link
Activity 3.3
Usefulness and
Harmfulness of Heat

measured?
important?
3.3 Why can expansion and
contraction be both useful and
harmful?

Objectives
 Infer that generally solids, liquids and
gases expand when heated and contract
when cooled
 Describe some consequences and
applications of expansion and
contraction in everyday life
 Appreciate science for its usefulness in
improving quality of life—knowledge of
heat allows us to tap on its usefulness
and reduce its harmful effects

Expansion and Contraction
 One way to open the tight metal cap of
a bottle is to heat up the cap. The cap
will expand and become loose.
using expansion to open
a tight bottle cap

Expansion and Contraction of
Solids
Activity Book Link
Activity 3.4
Expansion and
Contraction of
Solids

Expansion and Contraction of
Liquids
 Liquids also expand when they are heated and
contract when they are cooled.
 Generally, liquids expand more than solids
when heated and contract more when they are
cooled
Activity Book Link
Activity 3.5
Expansion and Contraction of Liquids

Expansion and Contraction of Gases
 Gases expand when heated and contract when
cooled.
 Generally, gases expand more than solids and
liquids when heated. Gases contract more than
solids and liquids when cooled.
air expands when heated and contracts when cooled
Activity Book Link
Activity 3.6
Expansion and Contraction of Gases

Effects of Expansion and
Contraction
 Expansion and
contraction involve
very large forces
which can cause
harm and damage to
buildings and
structures.
 Railway tracks are
often laid with gaps to
allow spaces for
expansion and to
prevent buckling.
railway tracks that have
buckled under the hot sun

 In HDB estate, there is a requirement for
gaps between floor tiles to be between 2 mm
and 4 mm* to allow for expansion in hot
weather.
 Otherwise, the tiles will crack and pop out
when they expand.
expansion gaps between floor
tiles in HDB estates

 The force of contraction can also cause
damage.
 Overhead cables are installed with extra
length so that they will not snap when they
contract during cold weather.
overhead cables contract when they are cooled

Benefits of Expansion and
Contraction
 Expansion and contraction are used in
riveting and bimetallic strips.
bimetallic strips are used in thermostats to control temperature such as in rice
cookers, electric irons and electric ovens

Riveting
 Riveting is
a method
used to
hold two
pieces of
metal
tightly
together

What is a bimetallic strip?
 A bimetallic strip
consists of two
strips of
different metals
joined together.
 At room
temperature, the
strip is flat. When
heated or
cooled, the
bimetallic strip will
bend.
a thermostat which is used to
control the temperature of an oven

Bimetallic Strip
 When heated, the
brass strip expands
more than the iron
strip, causing the
bimetallic strip to
bend.
 When cooled, the
brass strip contracts
more than the iron
strip, causing the
bimetallic strip to
bend in the opposite
direction.
a bimetallic strip made of brass and iron

Lss module 1 chpt 3 investigating heat

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