"Perimeter of a Circle" PPT courseware on the circumference and area of ​​a circle

Description

"Perimeter of a Circle" PPT courseware on the circumference and area of ​​a circle

teaching objectives

1. During activities such as observation, discussion, and measurement, experience the process of exploring pi and summarizing the formula for the circumference of a circle.

2. Recognize pi, understand and master the circumference formula of a circle, and be able to use the circumference formula to calculate correctly.

3. Experience the close connection between mathematics and daily life, understand the history of the exploration of pi, and inspire national pride.

Discuss

(1) When the wheel rotates once, whose car goes far? Why?

(2) What is the relationship between the distance traveled by the wheel in one revolution?

The distance traveled by the wheel in one revolution is the circumference of the wheel.

Measure the circumference and diameter of a one dollar coin.

Tell me how it can be measured?

Measure the diameter of a dollar coin

Method 1: Measure the circumference using the rolling method.

Method 2: Measure the circumference using the rope wrapping method.

Use a calculator to calculate how many times the circumference of a coin is approximately its diameter.

Circumference: 9.3cm Diameter: 3cm

9.3÷3＝3.1

The circumference of a one-dollar coin is approximately three times its diameter.

The circumference of any circle is always more than 3 times its diameter. This multiple is a fixed number, which we call pi, represented by the letter π (pronounced pài).

After precise calculations, we know that pi is an infinite non-repeating decimal.

π=3.141592653……

When we calculate, we generally only take its approximate value (retaining two decimal places), that is: π≈3.14.

If C is used to represent the perimeter, then C= πd or C=2πr.

practice

1. Find the circumference of each circle below. (Unit: cm)

2. A vegetable pile with a diameter of 35 cm, with 2 reinforced lead bars on it.

(1) How many centimeters is the length of a lead bar?

35×3.14 =109.9 (cm)

Answer: The length of a lead bar is at least 109.9 centimeters.

(2) How many centimeters are there in total between the two lead bars?

109.9×2=219.8 (cm)

Answer: The total length of the two lead bars is 219.8 centimeters.

3. When the hoop rotates 60 times, how many meters does it roll? (Round to one decimal place)

30×3.14×60=5652 (cm)

5652 cm≈56.5 meters

Answer: The distance it rolled is 56.5 meters.

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Update Time: 2024-09-28

This template belongs to Mathematics courseware Hebei Education Edition Sixth Grade Mathematics Volume 1 industry PPT template

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