Knowledge: Through the teaching of this course, students can understand the process of pebble formation and the geological function of rock weathering, transportation and rounding.

Ability: By analyzing the formation process of pebbles, students' reasoning ability, imagination ability, information search ability and autonomous learning ability are cultivated. Cultivate students' creativity and divergent thinking.

Emotion, attitude and values: stimulate students' interest and curiosity, as well as the spirit of inquiry, cultivate students' interest and attitude in inquiry, and make students realize that nature is constantly changing.

Teaching focus:

As we all know, the rocks on the high mountains fall down due to weathering, and are washed away by the water flow during the river transportation, and collide with each other to form pebbles.

Teaching difficulties:

Understand the process of pebble formation.

Teaching process:

Introduce new lessons and find problems by yourself;

I. Observations:

The students brought their own stones to see what they found. Guide students to compare pebbles with ordinary rock fragments and find out the characteristics of pebbles; Found that some are smooth and round, some are angular, some are large and small ...)

Show the picture (pebble picture) and tell: This kind of stone is called pebble. In this lesson, we will learn something about pebbles. (pebbles written on the blackboard)

Three. Dialogue:

What do you want to know about pebbles? Guide students to explore how pebbles are formed. Why is it so smooth and round? (Formation of blackboard writing)

Learn new lessons and explore problems by yourself;

1. Inspire students to think about the causes of pebbles.

1. Speak:

Where did you find pebbles? Guide students to understand the environment of the collection site and know that pebbles are at the water's edge. If they are not collected from the water, they will also be transported from the water and other places. At this time, relevant video materials can be used to help students understand the environmental characteristics of pebble formation. )

Talk:

Can you imagine how pebbles are formed? Why is it so smooth and round?

3. Students discuss and express their views. Students with different views can explain their own views, or debate among students, and finally sort out and summarize their own views, so as to determine the direction of exploration. )

Tell:

How are pebbles formed? Why is it so smooth and round? Let's take this problem down the river. Put a video or a courseware on the middle and lower reaches of the river. Please watch with the following questions. Discuss the results with the partners in the same group and report. You can print out the questions discussed and send them to students, and record them while watching. It is not only conducive to students' discussion, but also conducive to cultivating students' ability to record, summarize and summarize. )

Thinking about the problem:

(1) What are the characteristics of the rocks in the upper reaches of the river?

(2) What are the characteristics of rocks in the middle reaches of rivers? What's the difference between the shapes of these rocks and those of the upstream rocks?

(3) What are the characteristics of rocks in the lower reaches of the river? How are the shapes of these rocks different from those in the upper and middle reaches?

(4) Is the distribution of rocks regular?

5. Where did the stones in the river come from at first? How did they get into the river?

6. How did you get to the middle and lower reaches? (handling)

7. Why is it oval? (rounded)

8. According to the above research, what have you found? (Guide the students to infer that the pebbles in the river come from the mountains, are washed to the middle and lower reaches by the river, and become oval in the process of being washed by the river. )

2. Understand the weathering of rocks

1. Show pictures of Yunnan Stone Forest.

Ask questions:

Why ... lead students to speculate that nature is destroying rocks. )

3. Show courseware (2) Effects of temperature, water and plants on rocks

(1) Call:

Please watch with the following questions. Discuss the results with the partners in the same group and report. You can print out the questions discussed and send them to students, and record them while watching. It is not only conducive to students' discussion, but also conducive to cultivating students' ability to record, analyze and summarize. )

Thinking about the problem:

(1) During the day, rocks are very hot by the sun; At night, the rocks become very cold again; In summer, rocks are very hot by the sun, and in winter, rocks become very cold.

(2) When there are cracks in the rock, when it rains, rainwater will flow into the cracks. The water flowing into the cracks, some seeped down, and some existed in the cracks. What happens to the water in the crevices of rocks in winter?

(3) When it rains, the running water on the hillside will wash the soil into the crevices, and the soil and plant seeds blown by the wind may also fall into the crevices.

(4) What does the above phenomenon mean?

4. Students watch the courseware (2) (Guide students to discover that when rocks are heated, their volume will expand and their heat transfer ability will be poor. The surface of the rock is very hot, but the inside of the rock is very cold; The expansion degree of each part of the whole rock is also different. When a rock gets cold, its volume will shrink. Similarly, due to the different degree of cold from the surface of the rock to the inside of the rock, the shrinkage of all parts of the whole rock will be different. Before telling a story, students can finish Experiment 1 to make it easier for students to understand. Due to the effect of cold and heat, all parts of the rock always expand and contract unevenly, and the internal structure will be destroyed, resulting in cracks on the rock surface; In winter, the water in the rock cracks will freeze, and when it freezes, it will expand, and when it expands, it will produce a force to increase the rock cracks. When it rains, the running water on the hillside will wash the soil into the crevices, and the soil and plant seeds blown by the wind may also fall into the crevices. When the seeds have moisture, they will germinate at a suitable temperature and grow into plants. The deeper, longer and thicker the roots of plants are, the deeper and bigger the rock cracks will be. )

5. Fully understand weathering:

The destruction of rocks by temperature, water and plants is called weathering. After a long period of weathering, some rocks on the mountain will become powder, some will produce criss-crossing cracks, and some will collapse, roll down the hillside and fall into rivers in the valley.

Transition: How can the rocks that collapsed on the mountain and rolled into the river become bare pebbles?

3. Understand the role of river water transport and bypass.

1. Question:

What does the strength of water have to do with it?

2. Discussion:

(1) When it rains heavily or rainstorm, the rainwater falling on the hillside will soon flow into the river. What do you think will happen to the stones in the river?

(2) The stones in the river are big and small, heavy and light, all of which are impacted by water. Will the result be different?

(3) Observe your experiment 2. What did you find?

(4) According to the above facts, what did you find?

3. Students discuss and report. Inspire students to discover that (running water is powerful, so the river has a kind of carrying function (blackboard carrying) to carry them from the upstream to the middle and lower reaches. The more rivers, the faster the speed and the greater the processing power. Large and heavy stones are transported relatively close; Small and light stones are transported far away. In the process of being carried by the river, the stones are washed by the river (washed by the blackboard water) and collide with each other (rubbed against each other on the blackboard), and the edges and corners are gradually worn away, and the volume gradually becomes smaller and becomes pebbles. )

4. Summarize the formation process of pebbles:

(1) Summary of teachers and students: The process of pebble formation is divided into two stages. The first stage is the weathering and collapse of rocks on high mountains, and the second stage is the rounding in the process of river transportation. These changes are gradual and take a long time.

(2) Fill in the blanks This lesson: The rocks on the mountain collapsed due to weathering, and were washed, rubbed and collided with each other by water during river handling, forming pebbles.

Four. Discussion:

Some beaches have boulders. How do you think they formed? Inspire students to infer how pebbles on the beach are formed according to the causes of pebbles on the beach. After long-term weathering and wave beating, the rocks along the coast have been broken and collapsed and brought to the beach by seawater; They were washed by the sea for a long time on the beach, and they collided with each other and formed pebbles. )

Specific model template

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