ciencias

Solar energy

The sun, a source of energy.

Earth does not emit its own light. It comes from the sun. The sun is constantly producing energy. This energy travels through space and reaches earth as heat and light.

Heat: it travels to earth by means o radiation. The sun’s rays reach different places on earth at different angles, that’s why there are hotter and colder areas.

Perpendicular rays= hotter diagonally rays= colder

Light: is a form of energy. The light that comes from the sun looks white, but is made up of many colors.

Light propagates in straight line and all directions, light travels at great speed.

Some objects allow light to pass through them, transparent.

Some objects do not let light pass through them opaque.

Some objects only let part of the light pass through them translucent.

Reflection: it’s when light changes direction when it hits and objects.

Refraction: it’s when light changes direction when it passes from one substance to another.

Earth is a magnet

· Magnets: are objects that attract iron and steel. This force of attraction is called magnetism.

· Electromagnets: are artificial magnets. They need an electric current to work.

Earth’s magnetic field

Earth is a giant magnet. Like all magnets, it has two magnetic poles:

· Earth’s magnetic south pole is in northern Canada

· Earth’s magnetic north pole is near the Antarctic coast.

solar energy

Matter and energy on earth

Mater changes:

Earth, like all other things, is made of matter. It has a lot of a mass and large volume.

Matter is made of many different substances (salt, water, wood etc…) these substances may be mixed together.

For example: seawater contains many salts.

Earth’s matter exists in three states:

Solid, like rocks

Gaseous, like air

Liquid, like water

Matter is constantly changing, these changes can be:

· Physical changes: some examples of physical changes of state, movement and fragmentation.

Changes of state are constantly occurring. For example, liquid lava comes out of volcanoes and becomes solid when it reaches the surface.

Earth is constantly moving. It rotates on its axis (rotation) and it orbits the sun (revolution). The matter on earth is also moving. Examples of movement of earth’s matter are:

· Tornadoes

· Oceans

· Water currents

· waterfalls

the movements of air and water break up water.

For example, the movement of waves breaks up rocks, and wind erodes soft rocks like limestone.

The external forces of earth.

Wind, water and people erode the relief of earth surface.

These changes occur slowly, over millions of years.

External changes happen in three phases:

1. Erosion: is the constant wearing away of rocks and soil.

Temperature, water, wind and people cause erosion.

· Sharp changes in the temperature: break rocks into fragments. This occurs in areas where there is a big difference between daytime and nighttime temperatures, such as mountains and deserts. Sometimes water that has filtered through cracks in rocks freezes. This act like a wedge and breaks the rock.

· Rainwater, rivers and oceans: constantly erode the ground.

Rain and snow dissolve the materials in the soil. Rivers wear away banks and erode materials from the rivers bed.

They create deep valleys and canyons. The waves of the ocean wear away the coasts. Underground water hollows out large caves.

· The wind: mostly erodes soft rocks. It also erodes places where there is a lot of sand, like deserts and beaches.

· The people: cut down forests. They cause fires, build slopes, etc. this actions cause erosion of the soil.

2. Transporting materials: eroded materials are transported from one place to another. The wind, river currents and ocean water transport these materials. Wind curries sand and small rocks. Rivers and oceans carry large amounts of dissolved materials. They also carry larger materials floating on the surface.

3. Sedimentation: occurs when the materials carried by water, ice or wind are deposited. The accumulation of these materials leads to changes in the lanscape.

· A river transports the materials. It deposits them on its banks to create terraces. It deposits at is mouth to create deltas.

· Ocean waves deposit materials on the low shores. The deposited materials create beaches.

· The wind transports large quantities of sand. This creates dunes in deserts and on the coast

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The internal forces of Earth

Earth changes: the relief of earth’s surface has not always been the same.

For example:

Islands and mountains have formed throughout time. Millions of years ago, there were plains where today there are mountains, and vice versa. Land now on the surface used to be under the ocean.

These changes occur as a result of the internal and external forces of earth.

Internal forces: create the surface relief.

External forces: erode the surface little by little.

Earthquakes: occur when internal forces break or move rocks inside earth. The rocks knock against each other and cause very intense and destructive seismic waves.

Earthquakes begin inside earth at a point called focus.

This point is called the epicenter on the surface.

The size or force of an earthquake is measured by a sale called richer scale and goes from 1 to about 9. The most intense earthquakes can change the lanscape.

Volcanic eruptions:

There are very hot substances inside earth. Sometimes these substances break through to the surface. They come out through to the surface. They come out through volcanoes.

The hot materials form magma. Internal forces put pressure on the magna and it rises through the central vert and comes out of the crater.

The substances that the volcano expels can be solid, like ash. They can also be liquid like lava. Volcanoes can also expel gases, which can cause explosions inside the volcano.

These expelled substances build up on the outside of the volcano and form volcanic cones. Sometimes volcanic eruptions can even create islands, such as the Hawaiian Islands.