Soil

24.1 How soil is formed
Soil is a mixture of decayed plants and animals, and small pieces of broken rocks such as sand, silt and clay. The rocks are broken as a result of a process called weathering.

Weathering
Soil is largely made up of weathered rocks. Weathering is the process that loosens and breaks down rocks at or near the surface of the Earth. It eventually converts the broken rocks into sand, clay, silt and other dissolved materials.

Weathering is brought about by various agents in our environment, such as:

• wind
• waves
• water
• heat from the sun
• plants and animal
• human activities
• frozen water

24.2 Soil erosion
The removal of soil by wind and rain is called soil erosion. soil erosion occurs when soil gets blown by the wind  or washed away by water.
Factors that affect soil erosion:

• speed and volume of running water
• amount of vegetation
• slope of  land
• dryness and size of soil particles

Effects of soil erosion:

• Shape of land
• condition of soil
• condition of water

How to prevent soil erosion

• Stop cutting down trees unnecessarily as this exposes the soil to the Sun, rain and wind.
• Grow plants and crops along the slopes of hills and mountains.
• build retaining walls to hold back slopes of hill and mountains.

Sound

23.1 Sound travels away from the source
Sound also travels in a similar way. When an object produces a sound, the sound travels away from the object in all directions. The object producing the sound is called the source of the sound.
23.2 Sound requires a medium to travel
Sound requires a medium to travel. When an alarm clock rings, we can hear the sound because the sound travels through the air and reaches our ears, In this case, air is the medium through which sound travels.

Electric Circuits

22.1 Electric Circuits
An electric circuit is made up of different components.
Which is:

• Energy source
• Wires
• Output device
• Switch

22.2 Circuit Diagram and Symbols
A circuit diagram is a drawing that uses different symbols to represent an actual electric circuit.
Symbols in an electric circuits

circuit diagram

22.3 Series and Parallel Circuits
We can classify electric circuits based on the arrangement of the components in the circuit. Electric circuits are classified into :

• Series Circuit
• Parallel Circuit

Series Circuit
A series circuit is a circuit that has components which are connected such that there is only one path for the electric current to flow through.




Parallel Circuits
A parallel circuit is a circuit that has parts which are connected such that there are more than one path for the electric current to flow through.




22.4 Brightness of a bulb
The brightness of the bulb in the circuit depends on the amount of electric current flowing through it. We can increase or decrease the amount of electric current flowing through the circuit by changing the:

• number of batteries
• number of bulbs
• arrangement of bulbs

Changing the number of batteries
connecting more batteries to the series circuit makes the bulbs light up brighter.
Changing the number of bulbs
connecting another bulb to the series circuit, without changing the number of batteries, can make the bulbs dimmer.
changing the arrangement of bulbs
connecting more batteries to the series circuit makes the bulb light up lighter.

Light and Heat

21.1 Refraction of light
Light travels in straight lines. However, when it travels from one medium to another for example, from air to water, it bends.

Dispersion of light through a prism
White light is actually made up of many different colors. we can prove this by shining white light through a prism.A prism a transparent plastic or glass object, with smooth flat sides that can refract light.

Dispersion of light through water droplets
Water droplets in the air can act as tiny prisms. The droplets can be from the rain, the mist of a waterfall or a fine spray of water from a garden house.

21.2 Transfer of heat
Just a light travels from one medium to another, heat also travels from one object or place to another. Heat travels from a region of higher temperature to a region of lower temperature through conduction, convection and radiation.

Conduction
Heat can transfer from one part to another within an object or between objects. This type of heat transfer is called conduction.

Convection
The transfer of heat from one region to another by the movement of fluids is knows as convection.

Radiation
Radiation is release of heat from the surface of most bodies that is transferred directly from one region to another.

Energy conversion

20.1 energy changes from one form to another
Energy cannot be created or destroyed, but it can be changed from one form to another.

20.2 Energy conversion in objects around us
The change of energy from one form  to another is called energy conversion. Energy conversion is important in objects around us. It provides objects with the forms of energy that require to do work

examples of energy conversion:

1. Burning Candle
2. Battery-operated Toy Car
3. Paper Airplane
4. Recorder
5. Guitar
6. Television Set
7. Speakers
8. Electric Fan

Gravitational and Frictional forces

19.1 Gravitational Force 
 Gravitational force is a force that can act at a distance from an object. It is the force of attraction between things and the Earth.

Effects of gravitational force 

Gravitational force is acting on us and all other objects all the time. It is because of the gravitational force that we are able to stand on the ground and not float away.
 

                                                                                           Gravitational force pulls the motorcycle back as

he tries to ride the motorcycle up to the mountain.

Weight of an Object

All objects on the Earth have weight. Objects have weight because of the gravitational force acting between them and the Earth.

                                                                    Differences:

                         Similarities:           -------->Weight is:
Weight-->                                     |             -a force

                Both can be measured--|             -the gravitational force acting on an object

Mass--->                                      |             -different at different places. The weight of an object is different

                                                     |             on the Earth, the moon and other planets

                                                     -------->Mass is:

                                                                   -not a force

                                                                   -the amount of matter in an object

                                                                   -constant. The mass of an object is the same, regardless of 

                                                                   where the object is.

19.2 Frictional force
Frictional force is a force that opposes motion. It is produced when two surfaces rub against each other.

Frictional force has many effects, it can:
@slow down and stop moving objects.
@prevent an object from starting to move.
@affect the movement of objects on different surfaces.

1.Frictional force can slow down and stop moving objects
When we push a toy car, the toy car travels for a short distance then comes to a stop. This is because there is frictional force acting between the tyres of the toy car and the table.





2.Frictional force may prevent an object from starting to move

when we try to push a car, we may find that it does not move. This is because frictional force is opposing the movement of the car.











3.Frictional force affects the movement of objects on different surfaces

 There is greater frictional force between rough surfaces then between smooth surfaces. So, objects move more slowly on rough surfaces than on smooth surfaces.


Air resistance and Water resistance
Frictional force is also produced when objects move through air and water.

1.Air resistance
The frictional force acting on objects as they move through air or as air flows around them is called Air resistance. Air resistance pushes against a moving object and slows it down.




2.Water resistance
The frictional force acting on objects as they move through water is called water resistance. Water resistance pushes against a moving object and slows it down.

Frictional forces can be useful and can cause problems
We can see frictional forces acting around us all the time. Sometimes, frictional forces can be useful. At other times they can cause problems.

1.Frictional forces can be useful
Frictional forces is useful in our daily lives. Without frictional force, there will be no grip.

2.Frictional force can cause problems
Although frictional force is useful in many instances in our daily lives, it can also be a problem.

The moving parts of the machine rub against each other, creating frictional force. Machines need extra energy to work against friction. This causes excess heat to be produced. Due to this, the parts of the machine get worn out more easily.

Friction can cause problems because it causes objects to:
*Slow down
*Over heat
*Wear out

Ways to overcome friction
We can reduce friction between surfaces in many ways including the use of:
+ Lubricants
+ Oil

Air and Water

18.1 The Oxygen and Carbon Dioxide Cycle
Living things need a constant supply of oxygen and carbon dioxide in the air to survive. All living things need Oxygen and Plants need carbon dioxide. It goes through a cycle called the The Oxygen and Carbon Dioxide Cycle

Oxygen in the Air                   Carbon Dioxide in the air
Oxygen will not run out as there are plants.          Plants take in Carbon dioxide to do photosynthesis
When plants do photosynthesis oxygen is            dead animals or humans could produce carbon    
produced. In this way, oxygen is used up            dioxide.  Burning of fossil fuels and vehicles could also produce
by living things is replaced constantly.                  carbon dioxide.

The air around us is made up of:

                      Nitrogen
                      Oxygen
                      Carbon dioxide and other gases                                            Water vapor            
                    




18.2 The Water Cycle
Water never runs out on earth due to the water cycle. The water cycle is the continuous movement of water from the earth, to the sky and back to the Earth. Here is the Water cycle:

1. Rising into the Sky
The Water rises into the sky, it evaporates to the sky. This effects because of the Sun. The sun causes Lakes, Rivers, Reservoirs, Oceans and even water that is released by living things.

2. In the Sky
When the water vapor rises to the sky, it cools and condenses to form tiny droplets of water. When the tiny droplets of water gather, It turns into a cloud.

3. Falling Down
When the clouds have exceed the limits to gather the tiny droplets of water it becomes a nimbostratus cloud or should I say 'black clouds'. Then when the cloud is getting more heavy, the tiny droplets starts to fall as rain.

Importance of the Water Cycle
  Many living things need fresh water for their survival. This is important because we can know what are clouds made of then why there is rain.

  Human activities cause great harm to our environment. They also affect the water cycle.
Here are the examples for water cycle:

1. Deforestation

Deforation is the cutting of trees. Many trees are cutted know because humans are selfish. Deforestation contributes to global warming. Deforestation causes floods, landslides and an increase in the Earths temperature.







2. Burning of Fossil Fuels

Burning of fossil fuels in places such as factories, produces harmful gases that form acid when they mix with water. When it rains the gas will mix with with the rain creating an Acid Rain instead of normal rain. Acid rain can pollute the water bodies and can kill plants on Earth.




Experiment about water cycle:Workbook Page 37-38
18.3 A Mini Water Cycle
Materials needed:Ice Cubes, Petri dish, Beaker, Hot Water.


Steps:
1.Pour water inside the beaker.


2.Place the Petri Dish above the beaker.


3.Place a few ice cubes above the petri dish.


Explanation:
You can observe that the hot water inside the beaker evaporates until the base of the petri dish. When it reach the petri dish, it condenses to form tiny droplets of water. then when the base of the petri dish is heavily filled with water droplets, the water droplets will fall.