SMSA YEAR 7 SCIENCE NOTES BOOKLET

Non-renewable & renewable energy

Some energy sources are non-renewable (cannot be replaced in a short period of time). E.g. fossil fuels.
And some energy sources are renewable (can be replaced in a short period of time). E.g. solar energy,
hydroelectric energy, wind energy & tidal energy.
B) Forms of energy

There are many forms of energy:

Form of energy Brief description

 Movement energy.

 Occur in all moving objects.
Kinetic energy

 Fast moving object has more kinetic energy than a slow moving object.

 E.g. moving racing car.

 Energy we can feel.

Heat energy  E.g. burning fuel producing heat, change of electrical energy to

heat energy in electric kettle.

 Energy we can see.

Light energy  Plants need this energy to make food.

 E.g. lamps & burning fuel.

 Energy we can hear.
Sound energy

 E.g. radio.

 Energy that makes electrical appliances work.

Electrical energy  It can change to other form of energy (kinetic, sound, etc).

 E.g. vacuum cleaner.

 Food, fossil fuels & batteries contain this form of energy.
Chemical energy  It can change to other forms of useful energy.

 Energy comes from substances such as Uranium & Plutonium. Page51
Nuclear energy

 Produces a lot of energy.
 One kind of stored energy.
Potential energy  It can change into other form of energy.
 E.g. stretched spring.

C) Energy changes

Energy changes from one form to another.

Some examples of energy changes are: animal, digestive system, breathing system and reproductive

system.

Energy change Example(s)
Potential energy  kinetic energy Winding up toys, diving

Electrical energy  kinetic energy A moving electric cart

Potential energy  kinetic energy + sound energy Piling

Chemical energy  heat energy + light energy Striking a match

Light energy  chemical energy Photosynthesis

Chemical energy  kinetic + heat + potential energy Space shuttle taking off

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Energy Converters

An energy converter changes energy from one form to another form.

E.g. car engine (changes chemical energy (from petrol) into kinetic
energy), electric motor (changes electrical energy into kinetic energy).
Application of energy converts in making electricity

Energy converts can be used to make electricity.

Some examples includes:
(a) Electricity from dynamo.

 A dynamo is an energy converter which changes kinetic energy into electrical energy.
 How it works?

(i) Dynamo turns then electricity is made.
(ii) Energy change: Kinetic energy  Electrical energy.
(b) Electricity from steam.
 A power station makes electricity.
 How power station works?
(i) Coal, oil or natural gas burnt to give heat thus boils water to make steam which turns

generators.

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(ii) A generator is a large dynamo – energy converter which converts kinetic energy into electrical
energy.

(iii) Overall energy change: Chemical energy  Electrical energy.
(c) Electricity from moving water.

 Electricity from water is called hydroelectricity.
 How it works?

(i) Energy change: Kinetic energy  Electrical energy.

(d) Electricity from electrical cells.
 A cell is an energy converter which changes chemical energy to electrical energy.
 Energy change: Chemical energy  Electrical energy.
 There are 2 types of cells: dry cells & wet cells.
 A collection of cells which are connected together is called a battery.

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Conservation of energy
When a certain amount of energy changes, the same amount of energy appears in the other form.
Therefore, we cannot create or destroy energy; this is called as conservation of energy.
ENERGY CAN BE CHANGED FROM ONE FORM TO ANOTHER BUT IT CANNOT
BE CREATED OR DESTROYED.
Measuring energy.
 Energy is measured in units called Joules. The symbol is J.
 The joule is a small unit. A larger unit is kilojoules (kJ).
 1 kJ = 1000 J

Energy from fuels.
- The main fuels are oil, coal and natural gas.
- They are called fossil fuels – made from dead plants & animals millions of years ago.
- How oil & natural gas were made?

Energy changes in fuel:

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Alternative energy sources

Some examples include:
(a) Wind energy – has kinetic energy. Uses wind turbine (about 2000 wind turbine) to produce

electricity.

(b) Tidal energy - a tidal power station which makes electricity as the tide moves.

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(c) Geothermal energy – underground water flows onto hot rocks & turns into steam. The steam is used
to generate electricity which is called as geothermal power station.
* Jet of steam from the ground is called geyser.

(d) Solar energy – energy from the sun. It can be used in several ways. E.g. solar panels, satellite solar
array, calculator, etc.

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(e) Nuclear energy
– Substances like uranium give out heat by themselves. This energy is called nuclear energy.
– Water flows in pipes past the uranium & boils the water to make steam thus turns the turbine.
- Care must be taken when using nuclear energy as it produces dangerous waste & radiation.
- Radiation can cause cancer.

(f) Biomass
– Plant and animal material is called biomass.
– In the ground, biomass decay & can make a gas called biogas.
– The biogas is good for heating and cooking.

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TOPIC 8: MAGNETISM
1.1 Magnets and Non-magnetic materials
Different kinds of magnets

When a magnet is at rest, it will come to rest in North-South direction.

Like poles REPEL
Unlike poles ATTRACT
Investigating magnets
Iron filings are attracted to the ends of the magnet.
The ends of the magnets have the strongest force of attraction.

Iron filings
Magnet

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Magnetic materials 2. Steel 3. Nickel 4. Cobalt
A magnet is able to attract objects that are made of : 1. Iron

Non-magnetic materials 4. Copper 5. Aluminium
Materials that are not attracted by magnets.
e.g.: 1. Rubber 2. Plastic 3. Wood

To distinguish between a magnet and non-magnetic materials

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8.3 Magnetic Field
Magnetic fields is a region of space around a magnet which attracts magnetic materials.
When iron filings are sprinkled around a magnet, the pattern they form shows the lines of force present in
the magnetic field.

When lines of force are close together  magnetic field is strong.
When lines of force are further apart magnetic field is weak.

If two magnets are close together, different magnetic fields are formed.

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