The Awesome Figures of Circles Screen Bean Says, “Circles Are Awesome Figures in Our World!” Circle, Diameter, Radius, Circumference, Pi Presentation by Bobbie J. Taylor 2009
Objectives Understanding Some Measurements of Circles What are the measurements inside, around, and across a circular swimming pool? • Circle • Diameter • Radius • Circumference • Area • Pi • Practice Makes Perfect
WHAT IS A CIRCLE? The kids say, “Screen Bean first needs to know the definition of a circle.” A circle is a closed flat figure in which every point is the same distance from a given point, called the center of a circle.
Diameter and Radius A O B Next, Screen Bean, you should know the diameter and radius of a circular pool. A 5 m 10m Diameter Diameter describes both a line segment through the center of a circle with endpoints on the circle and the length of that line segment. The diameter of a circle is always 2r. Radius Radius is any segment that has one endpoint at the center of the circle and the other endpoint on the circle. The radius is always ½d.
Circumference and Area Wait, Screen Bean, you need to know the definition and formula for circumference and area of a circle before you swim across the pool. • Circumference is the distance around a circle. • Area is the distance within a circle. • The formula for a circumference of a circle is π*d or 2π*r. • The formula for area of a circle π*r2. • Pi is approximately 3.142
Pi Pi Pi comes from the Greek letter pi which is written as π. Written as a decimal, pi is close to the decimal approximation, 3.141592653589793…
Practice Makes PerfectProblem Solving and Critical Thinking • What is the correct term for the distance across a circular swimming pool? • If Screen Bean wanted to know half the diameter of a circular swimming pool, what term is need? • Circumference measures what around a circular pool? • What formula can be used to find the area of a circle? • A swimming pool has a diameter of 100 m. What is its radius? • If a radius of a swimming pool is 30 ft, what is its diameter?
Summary Screen Bean says, “I have learned some basic measurements of a circle, and I’m now ready to swim the distance across the pool.” Screen Bean also thanks his teachers for explaining to him some geometric terms for circles and the awesome role circles play in our world.