radius diameter Circle A closed curved with all

radius diameter Circle A closed curved with all points • the same distance from center area origin circumference

Origin • The origin is the center of the circle. • All points on a circle are the same distance from the origin. • A circle is named by its center. • Name: Circle A origin A

Diameter • The diameter is the distance of a line segment going across a circle through its center. AB • It divides the circle exactly in half. • Is viewed as a line of symmetry. • Symbol is lower case d. diameter

Radius • Radius is the distance from the center of the circle to any point on the circle. • Radius is one-half the length of the diameter. • Symbol is lower case r.

Circumference • Circumference refers to the total distance around the outside of a circle. • Can also be called the perimeter of a circle. • Symbol is an upper case C.

Making Connections • You can estimate the age of a tree by measuring the circumference of a tree. For many kinds of trees, each 2 cm represents one year of growth. 100 cm

Making Connections • An odometer is an instrument used to measure the distance a vehicle travels by counting the number of wheel revolutions.

Properties of a Circle – Internet Activity SITE: SELECT: www. harcourtschool. com Math / Grade 7 / Glossary • For each word given, write a definition and illustrate an example. • Record work neatly and space between each definition. • title and date your page • Subtitle – Properties of a Circle (underline) • When you finish, go to site www. aplusmath. com • Select Games, then the 1 st Geometry Version of Non-Java Games. Words to Define circle, circumference, diameter, radius Tools Required pencil, eraser, ruler, red pen, disc, looseleaf

Circle Properties • closed curved • all points same distance from centre (origin) • radius • diameter • circumference • area • pi

Concepts you Should Now Know Origin • center of a circle Diameter • distance across center of circle (d) Radius • half the distance of diameter (r) • distance around the outside of a Circumference circle ( C ) Ratio of C & d • Circumference is actually 3. 14 ( ) bigger than the diameter or about 3 times bigger

Ratio Of The Circumference Of A Circle To Its Diameter • If you measure the distance around a circle (C) and divide it by the distance across the circle through its center (d), you should always come close to a particular value • We use the Greek letter to represent this value. (pi)

• Ratio Of The Circumference Of A Circle To Its Diameter The value of is approximately 3. 14159265358979323. . . • So, C/d always = ___ • Using is a quicker way to find the circumference of a circle. • Using allow us to calculate circumference with less measuring, (pi)

How Helps • Knowing the value of , allows us to use formulas to calculate 2 cm circumference. • If the diameter of a circle is 2 cm, how could you calculate the circumference? • C = x ___ • Estimate the circumference • The circumference is ____

Circumference of a Circle • C= x d • C = 3. 14 x 3 • C = 9. 42 cm If the diameter is 3 cm

Circumference of a Circle • C= x d Estimate Is. . . • C = 3. 14 x 1. 5 • C = 4. 71 cm If the diameter is 1. 5 cm

Circumference of a Circle • • • C = x d d =2 xr d =2 x 3 d =6 C = 3. 14 x 6 C = 18. 84 m C = x d …but we don’t know the diameter If the radius is 3 m

Circumference of a Circle • C= xd • C = 3. 14 x 5 • C = 15. 7 Estimate is. . If the diameter is 5

Diameter of a Circle What formula could I use? What is the diameter of a circle if the circumference is 18. 8?

Diameter of a Circle What is the diameter of a circle if the circumference is 13. 2?

Diameter of a Circle What is the diameter of a circle if the circumference is 33. 9?

Estimate the area of this circle.

Seeing the square units can help. Estimate is Remember each block is one square unit

Counting will not always give an exact answer. Actual is Counting square units can give you a good estimate, however, can be time consuming. The formula for finding the area of a circle is Estimate is xrxr or r A = 2

Pie are square? NO, pie are round!

Remember xrxr or r A = Estimated area is 2 Actual area is