FORCES AND ENERGY ACTIVITIES

USING ENERGY

We need energy.
We should only use the amount of energy we need.
There are two serious problems when we waste energy:

• Pollution. When we burn fuels, they produce carbon dioxide. This goes into the atmosphere and increases the temperature of our planet. This is called global warming.
• Depletion of fossil fuels. These fuels are not renewable.

ELECTRICITY

Electricity is produced at power stations.

• Thermal power stations use fuels such as coal, natural gas and petrol to produce electricity.
• Hydroelectric power stations use mechanical energy from falling water.
• Solar power stations use light energy from sunlight.
• Wind farms use mechanical energy from the wind.
• Nuclear power stations use nuclear energy from uranium.

FOSSIL FUELS

Coal, petroleum  and natural gas are fossil fuels.
We extract coal from mines and petroleum from oil fields.
Natural gas is found in deposits deep beneath the surface of the Earth.
Petroleum is used to produce fuels, plastics and other products.
Natural gas and coal are used directly as fuels to produce electricity.

SOURCES OF ENERGY

We use many types of energy from different energy sources.
There are two main types:

• Renewable energy sources. These sources never run out, for example, sunlight and wind, or they are continually produced in nature, for example, wood.
• Non-renewable energy sources. Examples are uranium and petroleum. These sources will run out one day because we use them up and they cannot be replaced.

THE TRANSFORMATION OF ENERGY

Energy can change from one type of energy into another.
This happens in nature and in many of the machines we use.

• In an electric fan, electrical energy is transformed into the mechanical energy of the moving parts.
• In a car, the chemical energy of the eptrol is transformed into thermal energy, then into the machanical energy.
• When you switch on a light bulb, electrical energy is transformed into light energy.
• In a toaster, electrical energy is transformed into thermal energy.

TYPES OF ENERGY

There are different types of energy:

• Chemical energy is the energy stored in food, in batteries and in fuels such as petrol and coal.
• Nuclear energy is found in some substances such as uranium and plutonium.
• Thermal energy is the energy which is given off in the form of heat.
• Mechanical energy is the energy used by electrical appliances and electronic devices.
• Electrical energy is the energy used by electrical appliances and electronic devices.
• Light energy comes from a source of light.

WHAT IS ENERGY?

We say that things have energy when they can make things change.
Batteries have energy.
The wind has energy.
Food has chemical energy.

Batteries (photo from mister bijou) 

Wind (Photo by Kim Hansen in Wikipedia)

Food (photo by epSos.de in Flickr)

GRAVITY

Objects always fall towards the centre of the Earth.
The force that makes things fall to the ground is called gravity.

HOW FORCES ACT

Normally, forces act when two objects come into contact.
Sometimes forces act when there is no contact between objects.
This happens with magnetic force.
A magnet can attract or repel objects from a distance.
Magnets have two ends, or poles.

• When we put the same poles of two magnets together, they repel each other.
• When we put the different poles of two magnets together, they attract.

Force of attraction: A magnet pulls iron objects towards it.

Force of repulsion: Repulsion means when things push apart from each other.

FORCES AND MOVEMENT

Forces make objects start moving.
They also make them stop moving.
To move a football, we put force on the ball with our foot.
If nothing stops the ball, it continues to move.
However, it moves more and more slowly until it stops.
This is because a force on the ground acts on the ball and slows it down.
This force is called friction.

REMEMBER

FORCES
Forces have different effects on objects.
They start things moving.
They stop things moving.
They change their shape.
They break things.