Lesson 10 Part 1
In science and technology, “energy” is one of the most important terms. In fact, we can’t live without energy. We need electrical energy when we use lights, computers, and any other electric appliances.
What is the largest energy source in our life? It is obviously the sun. The sun gives us light and heat energy. Plants use energy from the sun to grow.
Animals also need energy to live. When animals eat food, they are getting chemical energy from it. Cows and pigs, for example, eat plants and get energy from them. This means they are getting energy indirectly from the sun.
After all, when we eat meat and vegetables, we are also getting the sun’s energy.
What is the largest energy source in our life? It is obviously the sun. The sun gives us light and heat energy. Plants use energy from the sun to grow.
Animals also need energy to live. When animals eat food, they are getting chemical energy from it. Cows and pigs, for example, eat plants and get energy from them. This means they are getting energy indirectly from the sun.
After all, when we eat meat and vegetables, we are also getting the sun’s energy.
Lesson 10 Part 1-1
Where does Energy Come from?
Lesson 10 Part 1-2
In science and technology, “energy” is one of the most important terms.
Lesson 10 Part 1-3
In fact, we can’t live without energy.
Lesson 10 Part 1-4
We need electrical energy when we use lights, computers, and any other electric appliances.
Lesson 10 Part 1-5
What is the largest energy source in our life?
Lesson 10 Part 1-6
It is obviously the sun.
Lesson 10 Part 1-7
The sun gives us light and heat energy.
Lesson 10 Part 1-8
Plants use energy from the sun to grow.
Lesson 10 Part 1-9
Animals also need energy to live.
Lesson 10 Part 1-10
When animals eat food, they are getting chemical energy from it.
Lesson 10 Part 1-11
Cows and pigs, for example, eat plants and get energy from them.
Lesson 10 Part 1-12
This means they are getting energy indirectly from the sun.
Lesson 10 Part 1-13
After all, when we eat meat and vegetables, we are also getting the sun’s energy.
Lesson 10 Part 2
When we consume energy, does the energy disappear?
No. It only changes from one form to another. This fact is known as “the law of conservation of energy.”
Let’s take a light bulb for example. When electricity is flowing through it, the bulb becomes bright and hot. In other words, the electrical energy is being changed into light and heat energy.
Another good example is an electric motor and generator. General electric motors have coils and magnets. When electricity flows through the motor, its axis will spin. You can see this as electrical energy changing into kinetic energy.
On the contrary, if you turn the axis of the motor by hand, the motor works as a generator. When turning the axis generates electricity, kinetic energy changes into electrical energy.
No. It only changes from one form to another. This fact is known as “the law of conservation of energy.”
Let’s take a light bulb for example. When electricity is flowing through it, the bulb becomes bright and hot. In other words, the electrical energy is being changed into light and heat energy.
Another good example is an electric motor and generator. General electric motors have coils and magnets. When electricity flows through the motor, its axis will spin. You can see this as electrical energy changing into kinetic energy.
On the contrary, if you turn the axis of the motor by hand, the motor works as a generator. When turning the axis generates electricity, kinetic energy changes into electrical energy.
Lesson 10 Part 2-1
When we consume energy, does the energy disappear?
Lesson 10 Part 2-2
No. It only changes from one form to another.
Lesson 10 Part 2-3
This fact is known as “the law of conservation of energy.”
Lesson 10 Part 2-4
Let’s take a light bulb for example.
Lesson 10 Part 2-5
When electricity is flowing through it, the bulb becomes bright and hot.
Lesson 10 Part 2-6
In other words, the electrical energy is being changed into light and heat energy.
Lesson 10 Part 2-7
Another good example is an electric motor and generator.
Lesson 10 Part 2-8
General electric motors have coils and magnets.
Lesson 10 Part 2-9
When electricity flows through the motor, its axis will spin.
Lesson 10 Part 2-10
You can see this as electrical energy changing into kinetic energy.
Lesson 10 Part 2-11
On the contrary, if you turn the axis of the motor by hand, the motor works as a generator.
Lesson 10 Part 2-12
When turning the axis generates electricity, kinetic energy changes into electrical energy.
Lesson 10 Part 3
Imagine you have a hammer in your hand. You need energy to lift the hammer and hold it. But where did the energy go? The hammer has it. Though the hammer does not move as long as you are holding it, the hammer has energy as potential energy. If you release the hammer, it begins to fall. A moving object such as a falling hammer has kinetic energy. In the process of falling from a high position to a low position, potential energy changes into kinetic energy. In fact, the speed of the object increases as it comes down.
Why does an object in a high position fall? It is because the earth “pulls” objects. This is called gravitational pull, or gravity. The potential energy comes from gravity.
Why does an object in a high position fall? It is because the earth “pulls” objects. This is called gravitational pull, or gravity. The potential energy comes from gravity.
Lesson 10 Part 3-1
Imagine you have a hammer in your hand.
Lesson 10 Part 3-2
You need energy to lift the hammer and hold it.
Lesson 10 Part 3-3
But where did the energy go? The hammer has it.
Lesson 10 Part 3-4
Though the hammer does not move as long as you are holding it, the hammer has energy as potential energy.
Lesson 10 Part 3-5
If you release the hammer, it begins to fall.
Lesson 10 Part 3-6
A moving object such as a falling hammer has kinetic energy.
Lesson 10 Part 3-7
In the process of falling from a high position to a low position, potential energy changes into kinetic energy.
Lesson 10 Part 3-8
In fact, the speed of the object increases as it comes down.
Lesson 10 Part 3-9
Why does an object in a high position fall?
Lesson 10 Part 3-10
It is because the earth “pulls” objects.
Lesson 10 Part 3-11
This is called gravitational pull, or gravity.
Lesson 10 Part 3-12
The potential energy comes from gravity.
Lesson 10 Part 4
There are several ways to generate electricity. Solar cells, for example, change light energy (mostly from the sun) into electrical energy.
How about a hydraulic power plant? In a hydraulic power plant, generators are turned by water stored in a dam. In other words, the potential energy of water turns the generator and changes it into electrical energy. But where does the potential energy of water come from?
Water in a dam is originally rain or snow. How does it rain or snow? When water on the surface of the earth is heated by the sun, it becomes water vapor. When it goes up to the sky, it is cooled and becomes water again, and it eventually falls as rain or snow. Consequently, electrical energy from hydraulic power plants is transformed from the sun’s heat energy after all.
How about a hydraulic power plant? In a hydraulic power plant, generators are turned by water stored in a dam. In other words, the potential energy of water turns the generator and changes it into electrical energy. But where does the potential energy of water come from?
Water in a dam is originally rain or snow. How does it rain or snow? When water on the surface of the earth is heated by the sun, it becomes water vapor. When it goes up to the sky, it is cooled and becomes water again, and it eventually falls as rain or snow. Consequently, electrical energy from hydraulic power plants is transformed from the sun’s heat energy after all.
Lesson 10 Part 4-1
There are several ways to generate electricity.
Lesson 10 Part 4-2
Solar cells, for example, change light energy (mostly from the sun) into electrical energy.
Lesson 10 Part 4-3
How about a hydraulic power plant?
Lesson 10 Part 4-4
In a hydraulic power plant, generators are turned by water stored in a dam.
Lesson 10 Part 4-5
In other words, the potential energy of water turns the generator and changes it into electrical energy.
Lesson 10 Part 4-6
But where does the potential energy of water come from?
Lesson 10 Part 4-7
Water in a dam is originally rain or snow.
Lesson 10 Part 4-8
How does it rain or snow?
Lesson 10 Part 4-9
When water on the surface of the earth is heated by the sun, it becomes water vapor.
Lesson 10 Part 4-10
When it goes up to the sky, it is cooled and becomes water again.
Lesson 10 Part 4-11
And it eventually falls as rain or snow.
Lesson 10 Part 4-12
Consequently, electrical energy from hydraulic power plants is transformed from the sun’s heat energy after all.