第九课

9 The Secret of the Hot Balloon Rising热气球上升的秘密

1. Have you ever seen a hot air balloon?你见过热气球吗？

2. Why did the balloon lift off?热气球为什么会升空呢？

3. Material package: plastic bag, paper snake, thin thread, etc.材料包：塑料袋、纸蛇、细线等。

4. Activity process活动过程

5.  Explore the secrets of Hot Balloon Rising热气球里面是什么？

6. The reason for the rise may be that the···上升的原因可能是······

7. Do an experimental study. 做个实验研究一下吧。

8. Pay attention to safety when using fire!用火时要注意安全！

9. Why did the paper snake turn around? 纸蛇为什么会转起来？

10. When the air is heated, the volume expands, and the hot air is lighter than the same volume of cold air,空气受热后体积膨胀，热空气比同体积的冷空气轻，

11. So the hot air rises. 所以热空气会上升。

12. Hot air balloons use the principle of hot air rising. 热气球就是利用热空气上升的原理升空的。

13. Find out the rise of hot air in life.找一找生活中热空气上升的现象。

14. I also know我还知道······

15. Outreach activities拓展活动

16. How do people control the rise and fall of hot air balloons?人是怎样控制热气球升降的？

17. Check the data and find out.查阅资料，了解一下。