"Projection" Projection and View PPT Download (Lesson 2)

Description

"Projection" Projection and View PPT Download (Lesson 2), 16 pages in total.

learning target

parallel projection

orthographic projection

Lesson import

Take some small sticks and triangular and rectangular pieces of paper of different lengths and observe their shadows under the sun.

(1) Fix the projection surface and change the position and direction of the stick or piece of paper. What changes will happen to their shadows?

(2) Fix the stick or piece of paper and change the position and direction of the projection surface. What changes will happen to their shadows?

Gain new knowledge

Knowledge Points Parallel Projection

(1) At three different moments, the shadow length of the same tree is different. Please arrange them in the order of shooting and explain your reasons.

(2) At the same moment, what is the relationship between the length of the shadows of two trees and their heights? Communicate with peers.

1. Parallel projection

(1) Definition: The projection formed by parallel light rays is called parallel projection. For example, the shadow formed by an object under sunlight is parallel projection.

(2) Key points: ① The lines connecting corresponding points in parallel projection are parallel to each other.

② If the lines connecting the corresponding points of the object and the projection are parallel to each other, it means that it is a parallel projection.

③When an object is under sunlight at different times, not only the size of the shadow changes, but also the direction of the shadow changes. As far as the northern hemisphere where we live is concerned, the direction of the shadow in the morning changes from west to north, and the shadow becomes shorter and shorter; in the afternoon, the shadow direction changes from north to east, and the shadow becomes longer and longer.

Knowledge points Orthographic projection

1. Definition: The projection produced when the projection line is perpendicular to the projection surface is called orthographic projection. as the picture shows:

2. Key points: (1) Orthographic projection is a special parallel projection, it cannot be a central projection;

(2) Orthographic projection emphasizes the relationship between light and the projection surface, regardless of the position of the object;

(3) The shape and size of the orthographic projection of an object are related to the position of the object relative to the projection surface. It can be divided into three situations: parallel, inclined, and perpendicular to the projection surface.

Class summary

Characteristics and drawing methods of parallel projection:

(1) Characteristics: ① In parallel projection, the light rays forming the shadow are parallel, and the shadows formed by parallel objects on the ground are parallel or on the same straight line;

②At the same time, under sunlight, the height of an object is directly proportional to the length of its shadow.

(2) Drawing method: Connect the top of the object and the top of the shadow to get the light that forms the shadow. Draw a parallel line of known light through the top of the object to get the shadow of the object.

Keywords: Beijing Normal University Edition Ninth Grade Volume 1 Mathematics PPT courseware free download, projection PPT download, projection and view PPT download, .PPT format;

For more information about the "Projection and View Projection" PPT courseware, please click on the Projection and View PPT Projection PPT tab.

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Update Time: 2024-09-29

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