"Central Projection" PPT courseware

Description

"Central Projection" PPT courseware

learning target:

1. Go through the process of practice and exploration, understand the meaning of central projection, and master the nature of central projection.

2. Through observation and imagination, you can abstract the rules (key points) of the center projection of points, line segments, and plane graphics.

3. Able to identify the shadow and changing patterns of objects based on the light source, or determine the light source based on the shadow. (Test point).

shadow puppet

Shadow puppetry is a performing art that uses light to reflect the shadows on the screen (projection surface).

Hand shadow

Under the light, making different gestures can form various hand shadows.

The shadow puppets and hand shadows above are all shadows formed under the light.

Self-learning

Study the contents of textbook P160-161, understand the definitions and related concepts of projection and central projection, and complete the questions related to the tutorial plan.

Projection: Under the illumination of light, the shadow of an object in space falling on a plane can reflect the shape and size of the object. This phenomenon is called projection.

Knowledge points: point light source, point on the object and its corresponding point on the shadow. The three points are on the same straight line.

Center projection:

The projection of an object formed under a point light source is called the central projection. The point light source is called the center of projection. Its projection lines intersect at one point (projection center).

Experiment and exploration 1

Read P161 independently, complete the projection drawing, and think about the following questions:

(1) Think about it, what is the central projection of point A in the projection plane H?

(2) What shape is the center projection of the bamboo stick AB in the projection plane H?

1. The projection of point A on the projection surface H is a point;

2. The projection of line segment AB on the projection surface H may be a line segment or a point. (When the two endpoints of AB are on the same projection line)

Experiment and Inquiry 2

Properties of central projection:

Under central projection, when each plane figure is parallel to the projection surface, the projection of this plane figure on the projection surface is a plane figure similar to it. The similarity ratio is equal to the distance from the projection center to the plane figure and the distance from the projection center to the projection surface. ratio of distances.

Example 1 (1) As shown in the figure, when the kitten reaches point B, use a line segment to represent its shadow under street lamp A.

(2) When the kitten reaches point B, based on its shadow under street lamp A, determine its height and express it with a line segment.

(3) When the kitten reaches point B, the kitten and its shadow under street lamp A are as shown in the picture. In which direction do you think the position of the street lamp is, and how do you judge it?

Knowledge point 1: Point light source, point on the object and its corresponding point on the shadow. The three points are on the same straight line.

Exercise 1: At the same moment, the shadows of two wooden sticks are as shown in the picture. Please draw the shadow of the other wooden stick in the picture.

Exercise 2 A pair of twin sisters are exactly the same height. Please draw the shadows of the twins under the street lamp in the picture.

Knowledge point 2: When an object of equal height is placed vertically on the ground, the closer it is to the point light source under the light, the shorter the shadow of the object; the further away from the point light source, the longer the shadow of the object.

Class summary

Talk about your gains:

1. The concept and characteristics of central projection;

2. Properties of central projection.

(Meizhou, Guangdong) As shown in the picture, Xiaoliang is walking under the street lights at night. When Xiaoliang walks from point A to point B, his shadow on the ground ( )

A. Gradually become shorter B. gradually lengthen

C． First become shorter and then become longer D. First become longer and then become shorter

Consolidation exercises

1. The rays in parallel projection are _____ rays, and the rays in central projection are _____ rays.

2. The length of the shadow of wooden sticks of equal length under the sun at the same time (both perpendicular to the ground) is _____; the length of the shadow of wooden sticks of equal length under the light is _____; at this time, the length of the shadow is related to the distance from the light Relatedly, the farther away from the light, the more _____ the shadow becomes, and the closer to the light, the more _____ the shadow becomes.

3. As shown in the figure, there is a burning candle at A on the ground (the length is not counted). If a person moves between A and wall BC, then the length of his projection on the wall becomes smaller as his distance from the wall becomes _____( Fill in "get bigger", "get smaller" or "unchange").

4. In the plane rectangular coordinate system, a point light source is located at A (0, 5), the line segment CD⊥x-axis is at D (3, 0), and the coordinate of point C is (3, 1), then the shadow of CD on the x-axis The length is _____; the coordinates of the shadow of point C are _____.

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"Central Projection" PPT courseware 2:

"Central Projection" PPT Courseware 2 Teaching Objectives Through rich examples, understand the projection phenomenon in life, understand the concept of central projection, and feel the relationship between objects under central projection and their projections. By operating and observing thin bamboo sticks and parallelogram paper under the light...

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Update Time: 2024-11-21

This template belongs to Mathematics courseware Qingdao Edition Ninth Grade Mathematics Volume 2 industry PPT template

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