第20课

第20课

Lesson 20

滑轮

pulley

1.   国旗是通过什么装置升到旗杆顶端的呢 ？让我们准备些材料来研究吧 。

What device is used to raise the national flag to the top of the flagpole? Let's prepare some materials to study.

2.我们来研究滑轮 。

Let's study the pulley.

认识滑轮 。

Know the pulley.

    边缘有槽，可绕中心轴转动的轮子叫做“滑轮”。

A wheel with a groove on its edge that can rotate around its central axis is called a pulley.

    滑轮的种类很多 ，最基本的有两种 ：固定在一个地方，不能移动的滑轮叫做“定滑轮   ”；和重物一起移动的滑轮叫做“动滑轮 ”。

There are many kinds of pulleys, the most basic of which are two kinds: fixed in one place and immovable pulleys are called "fixed pulleys"; The pulley that moves with the weight is called "moving pulley".

组装滑轮 ，研究滑轮的作用 。

Assemble pulley and study the function of pulley.

使用滑轮真方便 ！

How convenient to use the pulley!

我们的滑轮 ……

 Our pulley

我还发现 ……

I also found that

我们的发现

Our findings

3.滑轮的应用 。

Application of pulley.

谁的力量大 ？

Who has the most power?

原因是什么 ？

What is the reason?

注意安全 ！

Caution!

4.做个小小起重机 。

Make a little crane.

观察生活中的轮子以滑轮有什么不同 。

Observe what's the difference between wheels in life and pulleys.