Circles (Unit 8)

AC DR Area Circumference Diameter Radius

Circles (Unit 8)Video – Learn Alberta

http://www.learnalberta.ca/content/mejhm/index.html?l=0&ID1=AB.MATH.JR.SHAP&ID2=AB.MATH.JR.SHAP.CIRC&lesson=html/

video_interactives/circles/circlesSmall.html

Construct Circles (Unit 8)Student outcome: I will be able to describe the relationship of radius, diameter and

circumferenceUse your compass to draw a circle…Use a ruler to find your radius first!

RadiusDistance from the centre of the circle to the outside edge…represented by “r”

DiameterDistance across a circle through its centre…represented by “d”

Construct Circles (Unit 8)Student Outcome: I will be able to describe the relationship between radius, diameter

and circumference

Question…• How can you find the diameter if you are given the

radius?

d = r x 2

Construct Circles (Unit 8)Student Outcome: I will be able to describe the relationship between radius, diameter

Question…• How can you find the radius if you are given the

diameter?

r = d ÷ 2

Let’s Construct Circles

Can you design the Olympic rings using a compass??

Let’s Construct Circles

Can you design the Olympic rings using a compass??

Rubric – Olympic Rings Rubric – Olympic rings

5 exact rings /5 5 exact rings /5

Parallel /2 Parallel /2

Straight Lines /3 Straight Lines /3

Spacing /Overlap /3 Spacing/Overlap /3

Neatness /2 Neatness /2

Total /15 Total /15

Practice (Homework)Page 271:

5c, 8c, 10, 11, 14

8ab 5c, 6c, 7c, 8c, 10, 11

5a, 6, 7, 8b, 10

Circumference of a CircleStudent outcome: I will understand radius, diameter, circumference relationships.

Circumference: is the distance (perimeter) around a circle.

Circular Object

Circumference Diameter How many diameters can you

fit around the circumference

(estimated)

Create an equation using “d”

Find The Circumference of Objects!

What is the relationship between the diameter and circumference of a circle?

Circumference of a CircleStudent outcome: I will be able to describe the relationship of radius, diameter and

circumference

Circumference: is the distance (perimeter) around a circle.

Steps:1. Wrap a piece of string around the objects circumference2. Then measure the string along the side of a metre stick.3. Then measure the diameter of your object and relate it to the circumference.

Find The Circumference of Objects!

Circumference of a CircleStudent outcome: I will understand radius, diameter, circumference relationships.

Circumference: is the distance (perimeter) around a circle.

C = 3 x d (estimated)

C = ∏ x d (actual)

What is the relationship between the diameter and circumference of a circle?

∏ is very close to 3 (friendly number)

http://www.learnalberta.ca/content/memg/index.html?term=Division03/Circumference/index.html

The “∏” is known as pi and is known as 3.14

Circumference of a CircleStudent outcome: I will understand radius, diameter, circumference relationships

Circumference: is the distance (perimeter) around a circle.

The “∏” is known as pi and is known as 3.14

DiameterEstimated

CircumferenceC= 3 x d

Actual Circumference

C= ∏ x d

5127

Circumference of a CircleStudent outcome: I will understand radius, diameter, circumference relationships

Circumference: is the distance (perimeter) around a circle.

DiameterEstimated

CircumferenceC= 3 x d

92133

Circumference of a CircleStudent outcome: I will understand radius, diameter, circumference relationships

Circumference: is the distance (perimeter) around a circle.

The “∏” is known as pi and is known as 3.14

DiameterActual

CircumferenceC= ∏ x d

21.98

370.52

703.36

Show Me What You Know# 1

The “∏” is known as pi and is known as 3.14

DiameterEstimated

CircumferenceC = 3 x d

Actualcircumference

C = ∏x d

10

3

15

Circumference of a CircleDid you KNOW?

The traditional Plains Indian powwow is an annualcelebration. People gather together for storytelling, singing,dancing and feasting. The powwow grounds are circles andthe performers dance around the circle in a clockwisedirection. How would you determine the distance a dancertravels in one complete trip around the circle?

Circumference of a CircleStudent outcome: I will understand radius, diameter, circumference relationships

PROBLEM:What if you were given the “radius.” Then how would you findthe circumference? (Remember...before we multiplied the diameter by

3)

The “∏” is known as pi and is known as 3.14

Radius(r) r + r = d

Estimated Circumference

C = 3 x d

Actual Circumference

C = ∏x d

27

12

Practice (Homework)Page 278-279:

2, 15, 16, 18, 19

10 2, 3a, 6, 11, 12, 13

1, 2, 3a, 5, 6, 7a, 9

Secret to the perfect pancake is discovered

http://phys.org/news/2014-03-secret-pancake.html#ajTabs

Practical Quiz #2Using a compass, design a 3 level (snowball) snowman.

One snowball has a radius of 2 cmOne snowball has a radius of 3 cmOne snowball has a diameter of 3 cm

Area means the total amount of space inside of a circle (or any shape).

Try to come up with an equation for a circle using the hints given...

What are the hints?• • • • • •

5 m

Area of a Circle

Area Equation is…

Answer is…there are roughly 3 squares (l x w) that fit into a circles. The remaining area outside of the circles roughly make up the area in the 4th part of the circle.

Actual Area Equation:Area = ∏r ²

5 m

Area of a Circle