第二单元

U2、busy site —— line and angle

二、繁忙的工地——线和角

Lesson One

第一课

What questions can you ask?

你能提出什么问题？

What are the characteristics of the light emitted by the car lamp?

车灯射出的光线有什么特点?

The light of the lamp is emitted from a point.

车灯的光线是从一点射出的。

The light is far away...

这条光线射得很远很远.....

The light from the lamp can be regarded as a ray.

车灯射出来的光线可以看作射线。

We have studied line segments before.

我们以前学习过线段。

Extend one end of the segment infinitely and get a ray.

把线段的一端无限延长，就得到一条射线。

Extend the line segment infinitely to both ends and get a straight line.

把线段向两端无限延长，就得到一条直线。

What is the difference between straight lines, line segments and rays?

直线、线段和射线有什么区别?

A line segment has two endpoints that can be measured; a line without an endpoint can be extended indefinitely...

线段有两个端点，可以度量；直线没有端点，可以无限延长......

After drawing two rays, what figure is formed?

过一点画两条射线，形成的是什么图形?

I draw like this, forming an angle.

我这样画，形成了一个角。

I draw this way, also formed a corner.

我这样画，也形成了一个角。

The drawing of two rays from a point is called an angle.

从一点引出两条射线所组成的图形叫作角。

Angles are usually represented by the symbol ∠. recorded as "∠1" and read as "

角通常用符号“∠”来表示。记作“∠1”，读作“角一”。

Lesson two

第二课

There are so many excavators on the construction site!

工地上有这么多挖掘机啊!

The angle on the bucket arm can be large and small.

铲斗臂上的角能大能小。

What questions can you ask?

你能提出什么问题?

Cooperative exploration

合作探索

How big is the angle formed by the excavator?

挖掘机形成的角有多大?

I know how to measure the length of segments,

我知道用   能计量线段的长度，

The area of rectangle and square can be measured by mouth.

用口能计量长方形和正方形的面积。

I guess ∠ can be used to measure the size of the angle.

我猜可以用∠计量角的大小。

I measure it with ∠1 on a triangle, three ∠ one.

我用三角尺上的∠1来量，有3个∠1那么大。

I measure it with ∠2 on the triangle ruler, bigger than 2∠2.

我用三角尺上的∠2来量，比2个∠2大一些。

I measured it with ∠3, five ∠ three.

我用折出的∠3来量，有5个∠3那么大。

The amount I use ∠4 is smaller than 2∠4.

我用折出的∠4来量，比2个∠4小一些。

In order to determine the size of the measurement angle, there should be a unified unit of measurement and measurement tools.

为了准否确测量角的大小，要有统一的计量单位和度量工具。

The commonly used protractor tool is the protractor.

常用的量角工具是量角器。

The unit of measurement of the angle is degree, expressed by symbol. Divide the semicircle equally into 180 parts, each of which has a diagonal angle of 1 degree, recorded as 1.

角的计量单位是“度”，用符号“°”表示。把半圆平均分成180份，每一份所对的角就是1度的角，记作1°。

There are two circles of scale on the protractor.

量角器上有两圈刻度线。

And a zero scale.

还有0°刻度线。

How to measure the angle of the protractor?

怎样用量角器量角呢?

The scale of the other side on the protractor is 60, and the angle is 60.

另一条边在量角器上所对的刻度是60，这个角就是60°。

The center point coincides with the vertex of the angle.

中心点与角的顶点重合。

The 0 scale coincides with one side of the angle.

0°刻度线和角的一条边重合。

Can you draw a 400 angle?

你会画一个400的角吗?

I draw like this.

我这样画。

What angle can the bucket arm form in the work?

铲斗臂在工作中可以形成什么样的角?

What are these angles?

这些角分别是什么角呢?

Let's do a corner study.

我们做个活动角研究。

What are the acute angle ,2 is a right angle ,3 is an obtuse angle, and what are the angles of 4 and 5?

①是锐角，②是直角，③是钝角，④和⑤各是什么角呢?

flat angle    round angle

平角          周角

Measure the degrees of the following angles. What do you find?

量一量下面各角的度数，你有什么发现?

The right angle is 90, the flat angle is 180, and the circumference is 360

直角是90°，平角是180°，周角是360°

1 flat angle =2 right angles     1 week angle =2 flat angles

1平角=2直角                1周角=2平角

Sharp angle less than 90, obtuse angle...

锐角小于90°，钝角....