LIGHT AND HEAT

Isaac Newton was an English scientist. He was born in 1642 and he died in 1726.

Isaac Newton accidentally discovered

gravity when he was under a tree and an

apple fell on his head.

Gravity is the force that the Earth has. It pulls objects

toward it.

The gravity of the Sun and the Moon pulls the Earth.

That is why we have two

low tides

and two high tides

He also showed that a white light through a prism can turn into seven

colours.

LIGHT SOURCES

They can be natural like the Sun, stars, lightnings, etc.

They can be artificial like light bulbs, torches, candles, etc.

CHARACTERISTICS OF LIGHT

1. Light travels at 300.000 kilometres per second.

If the distance between our Sun and the star of Alamak is 350 light years, the Sun is

3.452.929.200.000.000 kilometres away from Alamak.

2. Light is white but when it is refracted through a prism, it turns into 7 colours.

When there is sunlight and it rains at the same time, rain drops act like a prism. That is why we

can see the rainbow.

3. Light travels in a straight line.

4. When there is an obstacle, light can be:

Absorbed. Black clothes absorb light, so it is quite

uncomfortable to wear black clothes in summer.

Reflected. Reflection happens when light bounces off objects like mirrors.

Refracted. Refraction occurs when light changes direction, for example when it enters water.

MATERIALS AND LIGHT

Objects can be: TransparentTranslucent

Opaque

Transparent materials:All light can pass through them.

We can see clearly through them.Examples: glass.

Translucent materials:Some light can pass through them.We can see partially through them.

Examples: sunglasses.

Opaque materials:No light can pass through them.We cannot see through them.

Examples: wood, paper, walls, etc.

Opaque objects can absorb or reflect colours.

A tomato is red because it reflects the red and absorb the rest of the colours.

A pear is green because it reflects the green and absorbs the rest of the colours.

Black objects absorb all the colours but they don't

reflect any colours.

White objects reflect all the colours but they don't absorb any colours.

Snow reflects colours but doesn't reflect any of them.

REFLECTION

Reflection happens when light bounces

off and object.

When light hits a smooth surface, the rays reflect in

the same direction.

When light hits a rough surface, the rays reflect in different directions.

REFRACTION

Refraction happens when light changes direction because it has moved from one

substance to another.

Here, light has travelled from air to water.

But refraction also happens when: A light goes through a prism

Light travels from one substance to another

Light reaches lenses

Lenses are made of a

curved surface that refracts

light.

We can find lenses in :

TELESCOPES

MICROSCOPES

GLASSES