Wolfram Research
Wolfram Math World: Circle
This site from Mathworld provides a wealth of information about circles is presented. The information ranges from the basics--radius, circumference, etc.--to advanced concepts--equations in polar and pedal coordinates, etc.
National Council of Teachers of Mathematics
The Math Forum: The Cylinder Problem: High School Lesson
Using an engaging approach, this activity requires students to record the volume of cylinders as a function of the radius. Students will construct and measure the volume of several cylinders and then begin comparing these shapes.
CK-12 Foundation
Ck 12: Geometry: Pi
[Free Registration/Login may be required to access all resource tools.] Identify pi as the ratio of a circle's diameter to a circle's circumference.
Varsity Tutors
Varsity Tutors: Hotmath: Practice Problems: Circle Exercises
Twenty-five problems cover various circle activities. They are given with each step to the solution cleverly revealed one at a time. You can work each step of the problem then click the "View Solution" button to check each step of your...
Maths Challenge
Maths challenge.net: Curvature of the Earth
Distance problem using a spherical radius and height.
Texas Instruments
Texas Instruments: Direct Variation With Powers: Surface Area and Volume
Students find the approximate surface area and volume of an apple, measuring circumference 3 ways, using the mean of the measurements to find the radius. Each students enters the results in a Table on the board.
Texas Instruments
Texas Instruments: Math Today Coming Clean About Showering Time
In this activity using the USA TODAY Snapshot, "Coming clean about showering time," students will find the measures of central angles and arcs of a circle. They will use circumference, radius, concentric circles and degrees in a circle...
Discovery Education
Discovery Education: Web Math: Find Out Things About Circles
This WebMath site will assist with finding the radius, diameter, circumference, and area of a circle.
Khan Academy
Khan Academy: Praxis Core Math: Circles Lesson
A basic review of circles and how to calculate the circumference, radius, diameter, and area. Includes practice questions.
E-learning for Kids
E Learning for Kids: Math: World of Fish: Geometry
Students will play an interactive game to identify the circumference, radius, center, and diameter of circles.
Math2
Math2: Circles
This site has many useful formulas and examples relating to circles, including related definitions, circumference of a circle, area of a circle, length of a circular arc, area of a circular sector, equation of a circle in cartesian...
Calculator Soup
Calculator Soup: Tube Calculator
This calculator will calculate the various properties of a tube, also called a pipe or hollow cylinder, given 3 known values from variables of radii, circumference, wall thickness and height.
Calculator Soup
Calculator Soup: Sphere Calculator
This online calculator will calculate the 3 unknown values of a sphere given any 1 known variable including radius r, surface area A, volume V and circumference C. It will also give the answers for volume, surface area, and circumference...
Calculator Soup
Calculator Soup: Circle Calculator
Use this circle calculator to find the area, circumference, radius, or diameter of a circle. Given any one variable A, C, r or d of a circle you can calculate the other three unknowns.
Mocomi & Anibrain Digital Technologies
Mocomi: What Is Circle?
Discusses the radius, diameter, circumference, and area of a circle.
Science and Mathematics Initiative for Learning Enhancement (SMILE)
Smile: Diameter,circumference,radius & the Discovery of Pi
This site provides a good project for students to use to explore the circumference of a circle.
University of Cambridge
University of Cambridge: Nrich: Watching the Wheels Go `Round and `Round
Use the formula for the circumference of a circle to solve the challenge of this problem. The solution is available at this one page website.
ClassFlow
Class Flow: Area of a Circle
[Free Registration/Login Required] This flipchart reviews basic geometric forms in nature and real objects. Students are then given opportunities to find the area of circle and parts of a circle, given the radius and/or diameter of the...
Khan Academy
Khan Academy: Area of a Circle
Find the area of a circle given its radius, diameter, or circumference. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.
National Council of Teachers of Mathematics
The Math Forum: Multicultural Math Fair: Srinivasa's Spheres
Straightforward instructional activity that introduces students to pi by letting them measure real objects and solve a challenge problem. Includes instructions and a "Data Sheet" for keeping track of measurements. Available in English...
Varsity Tutors
Varsity Tutors: Hotmath: Practice Problems: Geometry in the Plane
Twenty-four problems presented on a variety of Plane Geometry topics. They are given with each step to the solution cleverly revealed one at a time. You can work each step of the problem then click the "View Solution" button to check...
Mr. Martini's Classroom
Mr. Martini's Classroom: Circles Geometry Review
This resource provides two levels of multiple choice questions to review the parts of a circle as well as area and perimeter.
Mathigon
Mathigon: Geometry: Circle and Pi: Degrees and Radians
Rather than dividing a circle into some number of segments (like 360 degrees), mathematicians often prefer to measure angles using the circumference of a unit circle - a circle with radius 1. This way of measuring angles is called...
Cuemath
Cuemath: What Is a Radian?
A comprehensive guide for learning all about radians with definitions, formulas, the arc length formula, angles, the circumference, the radius, solved examples, and practice questions.