"Why are wheels made round?" Circle PPT courseware 3

Description

"Why are wheels made round?" Circle PPT courseware 3

learning target

1. Experience the process of forming the concept of a circle, and the process of exploring the positional relationship between points and circles.

2. Understand the concept of a circle and the positional relationship between points and circles.

Why are round wheels stable?

The distance from any two points on the wheel edge to the axis center is equal, and the distance from any point to the axis center is a fixed value.

Memorize new knowledge

The concept of a circle: The figure composed of all points on the plane whose distance from a fixed point is equal to a fixed length is called a circle.

The fixed point is called the center of the circle

The fixed length is called the length of the radius (often also called the radius)

The circle with point O as the center is recorded as ⊙ O and pronounced as "circle 0"

Note: 1 From the definition of a circle, we can know that a circle refers to the circumference rather than the surface of a circle.

2. The elements that determine a circle are: center and radius.

There are three positional relationships between points and circles:

Point is outside the circle---the distance from the point to the center of the circle is greater than the radius

Point on a circle---the distance from the point to the center of the circle is equal to the radius

The point is inside the circle---the distance from the point to the center of the circle is less than the radius

Apply what you learn

1. It is known that the area of ​​⊙0 is 25π.

(1) If PO=5.5, then point P is at ________;

(2) If PO=4, then point P is at ________;

(3) If PO=________, then point P is on ⊙0.

Analysis: If the area of ​​⊙0 is 25π, then the radius of ⊙0 is 5

2. It is known that the circumference of ⊙O is 8πcm. If PO=2cm, then point P is at _______; if PO=4cm, then point P is at _____; if PO=6cm, then point P is at _______.

Link life

1. The physical education teacher wants to use a 3m long rope to draw a circle with a radius of 3m on the playground. Can you help him think of a way?

Solution: Fix one end A of the rope, then tighten the other end B (AB=3 meters) of the rope, and make a circle around A on the ground. The path taken by point B is the circle to be made.

Exercise questions

1. In △ABC, ∠C=90°, AC=BC=4cm, D is the midpoint of AB, with C as the center and the length of 4cm as the radius, draw a circle, then among the four points A, B, C and D, There is ( ) inside the circle

A.4 B.3 C.2 D.1

2. It is known that the radius of ⊙O is 6cm, and P is the midpoint of the line segment OA. If point P is on ⊙O, then the length of OA ( )

A. Equal to 6cm B. Equal to 12cm

C. Less than 6cm D. More than 12cm

3. The radius of ⊙O is 5, the coordinates of the center O are (0,0), and the coordinates of point P are (4,2), then the positional relationship between point P and ⊙O is ( )

A. Point P is within ⊙O B. Point P is on ⊙O

C. Point P is outside ⊙O D. Point P is on or outside ⊙O

Review, reflect, sublimate and improve

1. Definition of circle

2. Positional relationship between point and circle

If the radius of ⊙O is r and the distance from point P to the center O is d, then:

①If the point is outside the circle, then d >r;�

②If the point is on the circle, then d =r;

③If the point is inside the circle, then d

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For more information about the PPT courseware "Why are round wheels made round", please click the "Why are round wheels made round" ppt tag.

"Why are wheels made round?" Circle PPT courseware 4:

"Why are wheels made round?" Circle PPT courseware 4 Why are round wheels stable? (1) As shown in the figure, A and B represent the two points on the edge of the wheel, O represents the axis of the wheel, and the distance between A and O is What is the relationship between the distance between B and O? (2)C means on the edge of the wheel..

"Why are wheels made round?" Circle PPT courseware 2:

"Why are wheels made round" Circle PPT Courseware 2 Learning Objective 1. Experience and perceive why wheels are made round; 2. Know the definition and representation of a circle; As shown in the figure, A and B represent two points on the edge of the wheel , point O represents the axis of the wheel, the distance between A and O..

"Why are wheels made round?" Circle PPT courseware:

"Why are wheels made round?" Circle PPT courseware Why are round wheels stable? (1) As shown in the figure, A and B represent the two points on the edge of the wheel, O represents the axis of the wheel, and the distance between A and O is the same as B , What is the relationship between the distance between O? (2)C means on the edge of the wheel..

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Update Time: 2024-10-31

This template belongs to Mathematics courseware Beijing Normal University Ninth Grade Mathematics Volume 2 industry PPT template

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