Heat

•Heat as a form of energy . Heat
can make things hot and we can
use heat to do work.
•We feel hot when the Sun
shines. This shows that the Sun is
a source of heat energy and gives
out heat. Most of the heat on the
Earth comes from the Sun.

•Apart from the Sun, there are many other sources
of heat. Heat can be produced in many ways.
•Here are some activities to show possible heat
sources.

Heat sources Activities
•Rubbing or friction- •Rub your hands together
rubbing two objects against for some time and then
each other can produce hold them to your cheeks.
heat. Your cheeks will feel
warm, showing that heat
can be produced by friction.
Rubbing hands can produce heat

•Burning- when an •Burn a candle or a piece of
object burns, it paper and put your hands above
produce a flame that it. Your hands will feel
gives out heat. hot, showing that burning
substances can produce heat.
Burning substances can produce heat

•Electricity – when •Switch on the electric bulb for
electric current flows some time and place your hands
through a wire, heat is near the bulb. Your hands can
produced. feel the heat coming out from
the bulb.
Electricity can produce heat

•Heat can also be produced by:
a. Bending metal- bending a coat hanger or a
wire back and forth several times can
produce heat in the object.
b. Chemical reaction – after mixing solid
sodium hydroxide with water in a test
tube, the test tube will get warm.
c. Collision – when an iron nail is hit by a
hammer several times, the hammer and the
nail will get hot.

•Heat is a useful form of energy. We use heat to:
a. Cooking food
b. Drying clothes
c. Boiling water
d. Producing steam to generate electricity
e. Food drying for reservation
f. Providing warmth

•Heat is a form of energy. An object becomes hot when it
absorbs heat. Heat is measured in Joules (J).
•Temperature measures how hot or cold an object is. The
unit of temperature is degree Celsius ( C) or Kelvin (K).
Temperature can be measured with a thermometer.
•Heat and temperature are different.
•The table below shows the differences between heat
and temperature.

Heat Temperature
• A form of energy •The degree of hotness or
coldness of a body
•Heat can do work •Temperature cannot do work
•Measured in Joule (J) •Measured in degree Celsius (C)
or Kelvin (K)
•Transfer from a hot area to a Increases when heated and
cold area. decreases when cooled

•The amount of heat
•Objects with the same contained in an object
temperature contain the depends on
same amount of heat. a. The type of the
The higher the material that the
temperature of an object is made of.
object, the larger the b. The mass or the size
amount of heat of the objects, and
contained in it. c. The temperature of
the object.

•Heat only travels from a hotter object (or place)
to a cooler object (or place)
•Heat has several interesting ways of travelling:
It travel by three ways:
a. By conduction through solids
b. By convection through liquids or gases
c. By radiation through vacuum

•The flow of heat energy through solids such as metals
is called conduction.
•Heat energy uses molecules to help it to get around.
•For example, when a pan is heated, the molecules at
the bottom of the pan start to vibrate energetically.
They collide with their neighboring molecules and
cause them to vibrate faster. The passing of the heat
energy from one molecule to the next continues. In this
way, heat energy travels through the pan and then
through the food in the pan.

•Heat can flow through a liquid or a gas because
heated parts of the liquid gas move.
•Warm air rising above a heater is an example.
•The flow of heat that occurs when a warm liquid
or gas moves is known as convection.

•The process where heat energy travels through an
empty space or a vacuum is known as radiation.
•An example of radiation is the transfer of heat from
the Sun to the Earth through mostly empty space.
Such a transfer cannot occur via convection or
conduction, which requires the movement of material
from one place to another, or the collisions of
molecules within a material.

•Some natural phenomena occur as a result of
heat flow.
•Warming of the earth by the Sun
a. The Sun gives solar energy every day. During
the day, the Earth’s surface is warmed up
and during the night, this energy is radiated
back into space as radiant heat energy.

b. A fraction of the solar energy that reaches the
Earth is absorbed, causing evaporation of water
from the oceans, the lakes, the lands and plants.
Convection current carries the water vapour up
to the atmosphere to form clouds, which will
form rains and thunderstorms
c. The warming of the Earth by the Sun can cause
changes in the climatic conditions of the Earth
and many natural phenomena such as land ad
sea breezes, thunderstorms, hurricanes and so
on.

a. The unequal heating or air over land and water
will result in breezes near the shores.
b. During the day, both land and sea are heated by
the Sun. However, the land gets heated up
faster than the sea. The air above the land
surface heats up, expands and rises. It is lighter
than the surroundings air. To replace the rising
air, cooler air is drawn in from the surface of the
sea. This is the sea breeze. It can offer a
pleasant cooling effect on a hot afternoon.

c. At night, the land cools faster than the sea. When
this happens, the air over the warmer surface of sea
heats up and rises, pulling in air from the cooler land
surface to replace it. This is the Land breeze.

•A building can be kept cool by having a good
ventilation system, so that air circulation in the
building is ongoing. Hot air from the building flows out
from the top and cool air can flow in from the bottom.
•Most of the traditional houses are built with
ventilation holes at the base of the house and at the
top near the roof. Hot air inside the house will rise and
flow out through the ventilation holes at the roof. Cool
air will enter through the openings at the base of the
house to replace the hot air. This produces a natural
convection current inside the house.

•In modern buildings, the ventilation system is made
more effective by installing exhaust fans and extractor
fans. Hot and humid air can be sucked out and replaced
with fresh and cool air.
•Modern houses are equipped with fans and air
conditioners to make the house cooler. Modern
buildings use centralized air conditioning system to cool
the whole buildings.
•Insulation can also help to keep a building cool.
Buildings with loft insulation, insulating cavity walls or
double gazed windows are usually much cooler than
those which are built without insulating materials.

•When material allow heat to pass through them
rapidly, they are known as conductors. All metals are
good conductors of heat compared with other
materials.
•Other materials like- metals, liquids and gases that do
not allow heat to pass through easily are known as
bad conductors of heat or insulators.

Conductors Insulators
Mercury (liquid) Glass
Silver Air
Copper Water (liquid)
Aluminum Plastics
Zinc Rubber
Iron Wood
Lead Materials containing trapped air
( wool, plastic foam, expanded
polystyrene)

Examples of the uses of heat conductors in
daily life.
Materials/ devises Uses
Cooking utensils •Cooking utensils such as
saucepans, pots and kettles are
Insert image usually made of aluminum or
stainless steel.
kettle •They conduct heat quickly and
easily to the food as thus save
fuels.

Electrical appliances •Electrical irons and hot plates
are made of iron or stainless
Insert image steel that conducts heat well.
•Heat sinks that are used in
iron computers, disk drives and
televisions as cooling fins are
made of aluminum
Others •Radiator coils and cooling fins
behind the refrigerator are made of
Insert image copper.
•Soldering iron rods are made of
Soldering iron rods iron with copper tips.

Insulators are used in many applications where
we want to minimize heat flow or heat loss.
Materials/ devices Uses
Wood or plastics •Handles for cooking utensils, kettles,
teapots, soldering iron rods and so on.
•They protect our hands from the hot
surfaces.
Cork, asbestos sheets, tiles To prevent tabletops from being
damages by hot kitchenware or
objects.
Sawdust To cover ice blocks to slow down the
melting process.

Woolen blanket or cloth •Used to keep the body warm on cold
days. The woolen blanket and the air
layer trapped inside can prevent heat
loss from the body.
Fiberglass, expanded •Used as insulators in the walls of ice
polystyrene foam boxes and refrigerators. Air trapped
inside acts as insulator.
insulating cavity wall, Used in the buildings to prevent heat
double- glazed glass from entering by conduction during
Aluminum Plastics the day and prevent heat loss at
night.

There are many uses of heat flow in
our daily life:
a. The flow of heat through
conduction is used for cooking
and boiling. Conduction of heat
is also applied in electric irons,
ovens and toasters.
b. The flow of heat by convection
and radiation is used to dry wet
clothes, salted fish and others. Drying wet
clothes

c. Heat flow through radiation gives us hot water when
we use a solar heater to absorb heat from the Sun.
d. Convection currents can help to improve air
circulation and cool our houses and buildings. Fans and
air conditioners help to cool the surrounding air
through convection currents
Air conditioner.

e. Our life can be made healthier and more
comfortable with a good ventilation system in our
houses. Windows, opening and exhaust fans are things
that can help to improve the ventilation of air in a
house. Warm air inside the house can be drawn out
and replaced with fresh, cool air from the outside.

Ventilation of buildings