2.5 Fire as a source of energy

Natural sciences

Grade 4

Energy and change

Module 30

Fire as a source of energy

Activity:

To talk about ways fire is/has been used as source of energy

[lo 3.1, 3.2]

People discovered how to make fire very long ago. At first they used sticks found in the veld and rubbed these together long and hard, to make them warm. (You can do this to feel how warm they become.) When really hot, a spark would be generated and this could ignite dry leaves and grass. You can also feel the heat that is generated when you rub your hands together. Such rubbing is known as creating friction.

How could fire be used to help people?

Draw some pictures to show this. Add labels to explain your pictures.

Fire is still used for preparing food nowadays, and in enjoying time spent with friends. Think of how pleasant it is to chat around the fireside in the Kruger Game Reserve, or at home when you have a braai. Some people also use fire for keeping warm, and when we are camping all of us do this.

Some of the inhabitants of our country have nothing except fire for keeping warm in winter, because they have no electricity in their homes.

Discuss the picture with the help of the questions that follow:

• What do we call this source of energy and where can it be found?

• Why does a woman carry it? Where are the men?

• Name all the uses of this energy source?

Do you think it is safe for this woman to be looking for it?

• What are the disadvantages of this energy source, especially with regard to nature?

Imagine camping out. You are exhausted by the end of the day and would really like to have a cup of steamy soup. You do have soup, matches and a pot. You can pick up enough wood and twigs around the campsite.

When you make your fire, warm the soup and drink it, a scientific process takes place. When you lit the fire to burn the wood, chemical energy was changed into heat energy. The heat energy boiled the soup. When you ate the soup, your body changed the chemical energy in the soup to potential energy. Then your body changed it into kinetic energy (energy for movement) that is useful on a camping expedition. Your body changes energy. Some of the chemical energy that you obtain through food is changed into potential energy and then into kinetic energy. Some of the chemical energy is changed into heat energy to keep your body warm.

Fire is dangerous. Watch out!

Fire can also be very dangerous. You always have to take care when you use fire. We often read about or hear TV reports of people burning to death in their homes. Read the following news report:

Three young children were burnt to death in their hut over the weekend while their parents were at work. Bystanders and neighbours arrived too late to save the children who were calling out incessantly. They were trapped inside the hut by flames that had quickly spread through the whole hut. A strong breeze spread the fire through the neighbourhood and a further 25 huts were burnt to the ground.

Firemen who tried to stop the blaze discovered that the children had made a fire in a brazier, which presumably toppled over while they were playing around it and caused the damage.

Listen to the lesson to know which of the words in the list must go into the spaces in the sentences that follow below

(Word list: Copper, non-conductors, rubber, good, conductor, wood, steel, iron, plastics)

1. A material that allows heat to pass through is known as a .

1. Metals like , and

are heat conductors.

1. Other materials, like ,

and some are poor conductors and are known as

.

Non-conductors are valuable materials in many respects. Handles of pots and pans are made from non-conductors, so that our hands won’t get burnt when we are preparing food. Firemen wear special clothes that are made of non-conducting materials. This keeps fire from getting to their bodies.

Most of the energy obtained from fire is heat energy that becomes available when we burn fuel. The first fuel was wood, but burning coal provides a much warmer flame.

Fire was also used to melt wax to make candles, and to light oil lamps and torches.

When matches were discovered, the lives of people were made more comfortable. Why?

Paste a match into the space below.

Assessment

LEARNING OUTCOME 3: SCIENCE, SOCIETY AND THE ENVIRONMENTThe learner will be able to demonstrate an understanding of the interrelationships between science and technology, society and the environment.

Assessment Standard

We know this when the learner

• understands science and technology in the context of history and personal knowledge;

3.2 understands the impact of Science and Technology.

Memorandum

FIRE AS A SOURCE OF ENERGY

Discuss the picture with reference to the following questions:

• What is this source of energy called and where must one find it? We call it wood and we look for it in forests and in the veld.
• Why is a woman carrying it? Where are the men? In some cultures it is traditional for the women to gather the wood and carry it home, while the men tend the cattle.
• What can one do with this source of energy? Name all the uses you can think of. Any acceptable answer.
• Do you think it is safe for this woman to gather wood? No, there can be many dangers, such as snakes, wild animals, and thugs lurking in the woods.
• What are the disadvantages of this method, especially with reference to nature? It destroys our trees. Trees are damaged when branches are cut down.

Missing words

Materials that conduct heat are called conductors. Metals such as iron, steel and copper are good heat conductors. Other materials such as rubber, wood and some plastics are poor heat conductors. They are called non-conductors.

Non-conductors are valuable materials. The handles of pots and pans are made from these materials, so that we do not burn our hands when we prepare food. Fire fighters also wear special clothing made from these materials. It prevents the fire from touching their bodies.