"Projection" Projection and View PPT Courseware 4

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"Projection" Projection and View PPT Courseware 4

Do you know what the relationship between objects and shadows is?

When objects are illuminated by sunlight or lights, they will form shadows on the ground, walls, etc. It can be seen that shadows are closely related to the shape of objects.

An object and its shadow are so closely related. In mathematics, what is the shadow of an object?

projection

Generally, when an object is illuminated with light, the shadow obtained on a certain plane (floor, wall, etc.) is called the projection of the object.

The irradiating light is called a projection line

The plane on which the projection is located is called the projection surface.

parallel projection

Sometimes the light ray is a group of parallel rays, such as the rays in a beam of sunlight or searchlight. The projection formed by the parallel rays is a parallel projection.

For example, the shadow formed by an object under sunlight (referred to as the sun shadow) is a parallel projection. The direction of the sun's shadow can reflect the time.

lights and shadows

Discuss

1. The two pictures below are the shadows of two small trees at the same moment. Can you tell which picture is formed under light and which picture is formed under sunlight?

2. When Xiaodong walks under a street lamp, how does the length of his shadow change? Xiaodong walks on the road illuminated by the sun. How does the length of his shadow change?

3. Some people say that under the same street light, if the shadow of object A is longer than that of object B, it means that object A is taller than object B. Do you think this statement is correct?

Listen and practice

(1) There is a benchmark pole AB standing upright on the ground as shown in the figure. The length of the pole is 2cm.

①When the sunlight shines vertically on the ground, what shape is the projection of the benchmark on the ground?

②When the angle of inclination between the sun and the ground is 60°, what shape is the projection of the benchmark on the ground? And draw a projection diagram;

(2) There is a benchmark AB standing upright on the ground as shown in the figure. The length of the pole is 1cm. There is a small light bulb on the upper left to make the shadow of the benchmark. How will the shadow change if the benchmark moves to the right?

When Xiao Ming was practicing parallel bars on the playground, he found the shadow of the two horizontal bars on the ground during the practice ( )

(A)Intersect. (B) Parallel.

(C) Vertical. (D) Unable to determine.

Xiao Ming and Xiao Hua, who are the same height, stand in different positions under the light. If Xiao Ming is farther away from the light, then Xiao Ming's projection will be ______ than Xiao Hua's.

1. If a triangle is placed under sunlight, the projection it forms is ______, or it may be ______;

2. The light ray in parallel projection is ( )

A. Parallel B. Gathered together

C. Not parallel D. Diverging in all directions

3. On a sunny day, when Xiaoying was walking due north, she found that her figure was leaning to the left. Do you know that the time Xiaoying was at at that time was ( )

(A) Morning． (B) Noon.

(C)Afternoon． (D) Unable to determine.

4. At the same moment, two poles of different lengths are placed under the sun, but their shadow lengths are equal, then the relative position of the poles is ( )

A. Both are perpendicular to the ground

B. Two parallel poles inserted diagonally into the ground

C. The two poles are not parallel

D. One fell to the ground

summary:

1.What is projection?

Generally, when an object is illuminated with _____, the shadow obtained on _____ is called the projection of the object.

2. Classification of projection:

The projection formed by ______ is a parallel projection (such as sunlight, searchlight)

A projection formed by ______ is a central projection (such as a light bulb)

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Update Time: 2024-12-03

This template belongs to Mathematics courseware People's Education Press Ninth Grade Mathematics Volume 2 industry PPT template

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