2. Heat as a form of energy
• The Sun is the
primary source of
heat energy.
• Most of the Sun’s
heat is radiated back
into space and only a
small amount of it
reaches the Earth to
keep it warm.
3. Rubbing or Friction
• Heat can be produced
when two objects are
rubbed together.
• Example, the ancient
human produced fire
by rubbing two pieces
of wood together.
4. Burning
• Burning is one of the most common ways of producing heat.
• When something burns, it produces a flame and also heat.
11. The SI unit of temperature is Kelvin (K).
But we commonly use Celsius (oC) instead.
Conversion of Kelvin to Celsius:
Kelvin (K) = Celsius (oC) + 273
Example 1: Example 2:
55 Celsius to Kelvin 339 Kelvin to Celsius
Kelvin = Celsius + 273 Celsius = Kelvin - 273
= 55 + 273 = 339 - 273
= 328 K = 66 oC
12. Exercise 1: Exercise 2:
250 Kelvin to Celsius 383 Celsius to Kelvin
13. Heat vs temperature
Heat Temperature
A form of energy
The degree of
which flows from a
Definition hotness and coldness
hotter region to a of a body
cooler region
Joule (J) Unit of Kelvin (K)
measurement Celsius (oC)
- Increases when
Flows from a hot heated
Property
area to a cold area - Decreases when
cooled
14. The effect of heat
Heat only flows from a hotter object (or place) to
a cooler object (or place)
COOL HOT
Effects on Matter:
In general, solids,
liquids and gaseous:
(1) Expand when they
gain heat and;
(2) Contract when they
lose heat
15. Expansion & Contraction of Solids
COLD HOT
Expansion of Solids
As the temperature increases, the atoms vibrate
more vigorously and these vibrations push the
atoms further apart. Thus, the volume of the solid
increases.
16. HOT COLD
Contraction of Solids
When the solid is cooled down, the atoms vibrate
less vigorously and they become closer together.
Thus, the volume of the solid decreases.
17. Different solids expand and contract
at different rate
Metal A BIMETALLIC STRIP
Bimetallic strip
Metal B
(made up of two
different metals
strips welded
together) is used,
to find out how
different solid
expand or contract.
18. After heating, metal B expanded more than metal A.
This causes the bimetallic strip to bend.
Metal A
Metal B
19. METAL BALL & RING
When the ring and ball are at When the brass ring is heat, the
room temperature, the ball ring expands and the ball will
will not pass through the ring. easily pass through the ring
Metal ring
and metal
ball
Bunsen
burner
20. Expansion & Contraction of Liquids
COLD HOT
Expansion of Liquids
When the liquid is heated, the molecules have more
energy and move more vigorously. The movement of the
molecules overcome the forces of attraction between the
molecules, allowing them to move freely. Thus, the volume
of the liquid increases.
21. HOT COLD
Contraction of Liquids
At lower temperature, the molecules have less
energy and move closer to each other. This causes
the volume of the liquid to decrease.
22. Expansion and Contraction of Mercury
in the Thermometer
When the beaker is
heated, the water
molecules gains
heat and expands.
This causes the
mercury in the
thermometer to
rise.
23. Expansion & contraction of gases
COLD HOT
Expansion of Gaseous Contraction of Gaseous
When the gas is heated, the At a lower temperature, the
molecules gain more energy molecules have move slower
and move faster and further and have less energy. They are
apart. This causes the volume closer together causing the
to increase volume to decrease.
24. Expansion and Contraction of Gaseous
in Volumetric Flask
LIQUID
The experiment
LIQUID above shows that
gaseous expand
when heated and
glass glass contract when
air air cooled.
The liquid rises
Heat once the
volumetric flask
(a) Before heating
is heated.
(b) After heating
26. conduction
Conduction:
Heat transfer in
which energy of the
particles in the
warmer region is
Particles
of the passed on to the
fish particles of the
cooler region
Particle
s of the
pan
28. Region B
The particles from region
A passed on heat to the
particles of region B
A
B C
29. Region C
The particles of region B
will then pass the heat to
particles of region C
A
B C
30. States Of Matter
● The gaseous are very bad
in conducting the heat.
● This is because the
particles of the gaseous
are further apart.
● Therefore, the energy
passed on to the
neighboring particles is
slow
31. Metals are good heat conductor
● The particles in solid
are closely packed as
compared to those in
gaseous.
● Thus, more particles
can collide with each
other to pass on the
energy to their
neighboring particles.
32. Mercury is a good heat conductor
● Mercury, a metal and a liquid
at 20oC, conducts heat much
better than water.
● This is because they have
many electrons to move
about.
● When these electrons gain
heat, they move around
faster and collide more with
neighboring electrons and
atoms.
35. Application of conduction
(1) Increasing heat
transfer
Good heat conductors are
used to make electrical
appliances such as cooking
utensils and iron.
This is because, heat can
be transferred quickly
Heat from the source to
conductors targeted object
36. Heat
insulators
(2) Reducing Heat
Transfer
The handle of the
electrical appliances are
made from heat insulators
such as wood and plastic
to avoid unwanted
transfer of heat
37. Another example of
heat insulators used to
reduce heat transfer is
a cork mat.
It reduces heat loss
from the pan to the
table by conduction.
Cork mat
38. Double-glazed
windows reduce
heat gain from
outside the house
during the hot day .
It also reduces heat
loss from inside
during winter
season.
39. Air
Air is a good heat
Outside Inside insulator. Some air
are trapped between
two layers of glass
and this prevent heat
gain or heat loss
between outside and
inside of the house.
40. convection
Heat transfer by the circulation of currents from
one region to another in a liquid or a gas.
The cool water from the
top is denser than the hot Convection
water. This causes the cool current
water to sink.
When the water is heated
the hot water float
because it is less dense
than the cool water
Bunsen burner
41. Application of convection
Hang gliders
• The hang gliders can
fly without using any
energy to push them.
• They ride on air
currents.
• When ground gets
heated hot and
expands.
• The hot air rises from
the ground and lifts
the hang gliders in
the air.
44. Refrigerator
The freezer is usually located at the top of the refrigerator
FREEZER
The warmer air from bottom is
less dense thus floats to the top
The cold air from the freezer is
denser thus sinks to the bottom
45. HEATER IN A ROOM
COLD
WIND
The warmer air from the radiator is
less dense thus floats to the top
HOT RADIATOR
The cold air from the outside is denser
thus sinks to the bottom
46. RADIATION
The transfer of heat in the form of infrared waves emitted
by one body and absorbed by another body
Your hands feel hot
when placed close to
the flame, because
the heat from the
flame reaches your
hand by radiation.
47. In a similar way, the
heat from the Sun is
reaches the Earth by
radiation.
48. Radiate
Radiate Radiate
If the object is hotter than the surroundings,
it will radiate more heat than it absorbs.
49. Absorb
Absorb Absorb
If the object is cooler than the surroundings,
it will absorb more heat than it radiates.
50. The Rate of Radiation and
Absorption Depends On:
(1) Temperature
• The hot drink
radiates more heat
per unit time than
the cold drink.
• It loses heat more
quickly to the
surroundings than
the cold drink
52. (2) Nature of the surface
The hot water in the black
and dull cup loses heat
more quickly than the water
in the silver or white cup.
(a)Black and dull surface
- a good radiator of heat.
(b)Silvery (or white) surface
- a poor radiator of heat.
53. Application of RADIATION
Reducing heat gain
The fuel tank of the truck
has silvery surface to reflect
heat radiation and keeps the
fuels inside the tank cool.
54. Reducing heat loss
• Kettles and teapots usually have shiny and silvery
surfaces, which are poor radiators of heat.
• Thus, they will not lose heat too quickly by radiation.
55. Reducing heat loss or gain
• White or light colored
uniforms are commonly
worn in hot climate
places because white
surfaces reflect heat
well and are poor
absorbers of heat.
• This helps the students
cool on hot days
56. The space shuttle
and the space suit
of the astronaut are
white in color to
reduce heat gain
and heat loss.
57. Increasing heat gain
Solar heaters are painted
black to absorb heat
quickly from the Sun.
Black surfaces are good
absorbers of heat.
58. Efficiency in Preventing Heat Gain/Loss
A vacuum flask is
designed to
prevent energy
transfer between
the content
inside and its
surroundings
outside
59. Stopper The stopper is made
from cork or plastics
Vacuum
(heat insulators).
wall
This can prevent
Double heat loss and gain
glass shell
through conduction
Silver and convection
coating
Casting
60. Stopper The vacuum
Vacuum prevents any
wall energy transfer
Double through
glass shell conduction and
convection.
Silver
coating
Casting
61. Stopper
Double glass
Vacuum
wall shell reduces
heat gain and
Double
glass shell
heat loss by
conduction
Silver because glass is
coating an insulator.
Casting
62. Stopper
Vacuum
wall
Double glass
shell The silver coating
reduces heat gain
Silver
coating
and loss by
radiation.
Casting
63. Stopper
Vacuum
wall
Double glass
shell
Shiny or light
Silver
coating colored case
reduces heat
Casting
gain or loss by
radiation
64. EFFECT OF HEAT GAIN & HEAT LOSS
Why does the ice cube melt?
What changes when the ice
melts?
65. MELTING
• Matters can change its state when it is cooled or
heated.
• When a matter is heated, its particles absorbed heat
energy and vibrate or move faster
HEAT
SOLID LIQUID
66. Attraction forces
Solid has a fixed shape
because the molecules
are hold together by
attraction forces
between them
SOLID STATE
67. When a solid is heated,
the particles gain energy
and vibrate faster
70. BOILING / Evaporation
• Matters can
GAS HEAT change its state
when it is cooled
or heated.
• When a matter is
heated, its
particles
absorbed heat
energy and
vibrate or move
faster
LIQUID
71. LIQUID STATE
Until the attraction
forces between them fail
to hold them together in
their fixed position
72. Until all of the attraction
GASES STATE forces between them
break and allowing the
particles to move freely
73. differences
Boiling Evaporation
State at which change At any temperature and
At its boiling point only
occurs at any time
Throughout the liquid On the surface of the
liquid only
Where it takes place
Rate at which it takes
Quick process Slow process
place
Bubbles are formed Formation of bubbles Bubbles are not formed
Energy is supplied from
Source energy is needed Is energy needed?
the surrounding
74. condensation
• When a matter is
GAS HEAT cooled, its
particles emit heat
HEAT energy and vibrate
or move slower.
• If the released
energy is
sufficient, the
matter will change
its state.
LIQUID
75. When the temperature
drops, the particles
GASES STATE move slower and
become closer to each
other.
76. When the particles are
close enough to each
GASES STATE other, attraction forces
are formed between
these particles.
78. FREEZING
• When a matter is cooled, its particles emit
heat energy and vibrate or move slower.
• If the released energy is sufficient, the
matter will change its state.
HEAT
LIQUID SOLID
80. Finally all the particles
are bounded together
and it gives solid a
definite shape
SOLID STATE
81. sublimation
• Some substances change directly from solid to gas
or solid to gas without going through liquid state.
• Example: iodine, dry ice, sulphur and naphthalene.
SOLID STATE GAS STATE
During heating process, the particles of solid absorb the
heat and move about freely and far apart from each other.
The solid sublimates to a gaseous form.
82. Heating Curve Of Water
Temperature
GAS
BOILING POINT
Temperature where
liquid gas
LIQUID
Temperature where
MELTING POINT solid liquid
SOLID
Time
83. The Amount Of Heat Contained In
An Object Depends On:
(a) The type of
material of an
object
(b) The mass or size
of an object
(c) The temperature
of an object
84. What happens to the closely packed
atoms of the solid if expansion and
contraction occur frequently??
85. The undesirable effects
The expansion and
contraction during hot
day and cold night,
caused undesirable
damages to structures.
Cracks may appear on
concrete pavement.
86.
87.
88. Ways to reduce undesirable effects
Gaps between the
materials
The bricks or
concrete slabs are
arrange with some
gaps in between to
allow expansion in
the hot day and
contraction during
the cold night.
92. Sagging of the
transmission line
Electric transmission
cable sag on a hot day
due to expansion of
metals. However,
these cables lifted on
a cold night due to
contraction of metals
94. Bending of
the pipes
Pipes have bends in
them so they can
expand during the
hot days or contract
during the cold night
without cracking.
95. Application of expansion & contraction
(1) Riveting
A hot rivet is inserted When the rivet cools,
The end of the rive
through the holes it contracts and
is hammered to
of 2 metals, which pulls the metal pieces
form a new head.
are to be fastened tightly together
96. (2) Heat and Smoke Detector
The heat and smoke
detector uses the
application of heat
expansion of
bimetallic strip to
detect the presence
of heat during a fire.
97. ❶ The heat from the fire causes the bimetallic
strip to bend towards the contact point.
Bimetallic strip
Clamp Brass
Contact Iron
point
Battery
98. ❷ When the bending strip touches the contact
point to complete the circuit, the alarm rings.
Bimetallic strip
Clamp Brass
Contact Iron
point
Battery
99. (3) Hot air balloon
The hot air rises
because it is less
dense than the cooler
air in the surrounding
When the fire is
lighted the air is
heated & it expands
100. The cold air sinks
because it is more
dense than the cooler
air in the surrounding
When the fire is
turned off the air is
cooled & it contracts
