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.
Kamis, 26 April 2012
Rabu, 25 April 2012
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:
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:
- Burning Candle
- Battery-operated Toy Car
- Paper Airplane
- Recorder
- Guitar
- Television Set
- Speakers
- Electric Fan
Kamis, 19 April 2012
Gravitational and Frictional forces
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 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
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
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
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
Senin, 02 April 2012
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.
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 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:
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
2. Burning of Fossil Fuels
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.
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