LIGHT TRAVELS

Light travels in all directions at a speed of 300.000 kilometres per second.
We cannot see light moving.
Light travels in a straight line.
This is why we see shadows.

REMEMBER

ENERGY
There are many types of energy, from different sources.
Light energy comes from light.


EYES AND SIGHT
We need light in order to see.
Light enters the eye and passes through the cornea, the pupil and the lens.
Then, the retina captures this light and sends the information to the brain through the optic nerve.

Click here to remember what we saw last year.

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.