Natural Sciences Grade 7 - PowerPoint Presentation

Slide1

Natural SciencesGrade 7

Term 3: Energy and ChangeInsulation and energy savingSlide2

Topic 4Insulation and energy saving

Using insulating materials [part 1]

Natural Sciences - Grade 7Slide3

Using insulating materials

Materials that are heat insulators:

keep cold items cold; slow down heat transfer

from the surroundings;

keep hot items hot;

slow down heat transfer

from the hot item to the

cooler surroundings;

insulated window coverings

[awnings; curtains; blinds; etc.].

In summer it is closed [minimize heat gain] to cool the house and block out the sun’s radiation.In winter it is kept open to allow the sunlight through the house.

Natural Sciences - Grade 7Slide4

Types of insulators

Materials that contain air spaces

, are the best insulators.Examples:

-

thatched roof

[air is trapped in the spaces

between the grass of the thatch]

-

wool

-

cork - straw - feathers - grass -

styrofoam

Natural Sciences - Grade 7Slide5

Insulators are used to reduce heat transfer

StyrofoamIt is made from polystyrene

[a type of plastic; plastic is a poor conductor of heat].

It is also used to

make

food packaging

[picnics;

take-away meals; hot coffee; etc.].

The food in styrofoam boxes can

be kept warm

/ hot.

Natural Sciences - Grade 7Slide6

Insulators are used to reduce heat transfer

Ceiling insulationIt

minimizes heat gain during summer.

It

minimizes loss

of heat during winter.

It is

mostly made from fibreglass strands

[air is a poor heat conductor and it becomes trapped between the fibreglass’ strands ; the amount of heat loss/gain is limited; stops conduction and convection from taking place].

Foam can be sprayed

in the roof structure above the ceilings.Blanket insulation can be rolled out above the ceilings.

Natural Sciences - Grade 7Slide7

Insulators are used to reduce heat transfer

Materials that keep us warm

Woollen clothing prevents the body heat from escaping, e.g. jerseys; woollen hats; gloves; jackets; etc.

Bedding, e.g. blankets; duvets; comforters; etc.

It

keeps people warm when it is cold.

The air is trapped between the

fibres

and therefore

extra insulation

is given.Thermal jackets worn by Russian, Eskimo and Norwegian people keep them warm in temperatures that are below 0°C.

Natural Sciences - Grade 7Slide8

Insulators are used to reduce heat transfer

Insulating vacuum flasks and cool boxes

Insulating materials such as plastic and styrofoam are

used to make cooler boxes

[foam / sponge materials are excellent insulators. They have many air bubbles in the foam. Air is an excellent insulator.

Liquids

are

kept hot or cold in vacuum flasks.

Between the flask and the

casing

is a vacuum, meaning no air particles.Natural Sciences - Grade 7Slide9

Insulators are used to reduce heat transfer

Water pipes

-

Cover water pipes

with an insulating material to:

prevent water from freezing and water pipes from bursting as well

as preventing water waste.

prevent loss of heat through the metal pipes and reduce electricity waste.

- Water pipes are made from plastic materials [PVC].

Doors

Fill the gaps of fitted doors with foam rubber [weather strips] to prevent warm air from escaping.Walls

Build outer walls with a double layer of bricks

[cavity walls - air space reduces heat transfer].

.

Natural Sciences - Grade 7Slide10

Insulators are used to reduce heat transfer

Traditional / Indigenous homes

Roofs and some walls are made of grass which is a good natural insulator.

The framework is smeared with mud.

Floors are made from cow dung [dries and form a hard, waterproof floor and it is heat insulating].

Rondavels are build with thatched grass roofs [Xhosa]; beehive huts [Zulu].

Natural Sciences - Grade 7