National Council of Teachers of Mathematics
The Math Forum: Circles
Various forms of equations of circles are presented at the Math Forum: center-radius form, general form, diameter form, three-point form, and parametric form.
Illustrative Mathematics
Illustrative Mathematics: G Co Classifying Triangles
The goal of this task is to help students synthesize their knowledge of triangles where only two of the vertices have been given. They will need to know that a triangle inscribed in a circle, with a diameter of the circle as one side, is...
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...
Cuemath
Cuemath: Radius
This reference tool explores the radius of a circle. Provides definitions, solved examples, and practice questions with answers.
TryEngineering
Try Engineering: Tinkering With Tops
Lesson explores the history, design, and motion of spinning tops. Student teams design and build their own tops that can spin for at least 10 seconds within a circle 30 centimeters in diameter.
Mangahigh
Mangahigh: Pyramid Panic: Basic Shapes to Advanced Geometry
Guide a mummy safely through the burial chambers of a pyramid as you solve length and area problems in basic to advanced geometry. There are four game zones that deal with circles and triangles, quadrilaterals, the Pythagorean Theorem,...
Learning Wave Communications
Learning Wave: Geometry, Section 2
Geometry concepts are briefly discussed at this site, including volume of a cylinder, parallelograms, circles, trapezoids, and triangles. Sample problems and applications are included for practice.
CK-12 Foundation
Ck 12: Geometry: Tangent Lines
[Free Registration/Login may be required to access all resource tools.] This concept teaches students about tangent lines and how to apply theorems related to tangents of circles.
Homeschool Math
Homeschool Math: Circles
Lesson presents definitions of terms associated with circles and helps students learn to use a compass to draw circles and simple circle designs.
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.
ClassFlow
Class Flow: Circles Geometry
[Free Registration/Login Required] Students identify segments and lines related to circles and the properties of a tangent to a circle.
PBS
Pbs Mathline: Bubble Mania Lesson Plan [Pdf]
Determine the area, diameter, and circumerfence of a bubble residue by creating a soap solution and blowing bubbles.
Curated OER
Web Math: Find Out Things About Circles
WebMath offers a great site for students to practice finding the diameter, area and circumference of a circle.
University of Cambridge
University of Cambridge: Maths and Sports: Sports Equipment
Sports such as hockey, football, basketball and tennis use balls of different sizes. Can you arrange a selection of different balls in a line each touching the next to make the shortest line? This activity offers opportunities for...
University of Texas at Austin
Mathematics Teks Toolkit: Exploring C/d= Pie
A collection of circular objects will be used to explore circumference and diameter of circles.
Alabama Learning Exchange
Alex: Circling Around
Students will calculate the diameter, circumference, and ratio of a real world object. Students will create an electronic slideshow to illustrate the process of determining the diameter, circumference, and ratio of these objects.
Other
Paper Plate Education: Serving the Universe on a Paper Plate
Excellent resource for "paper-plate" activities that help simplify various astronomy topics. Learn how to build a "Moon Finder" and "Planet Pointer," and create a paper-plate model that explains the Transit of Venus.
Texas Instruments
Texas Instruments: Real Life Real World Avalanche Rescue
When hikers and skiers go into terrain with a risk of avalanches, they take safety equipment including avalanche rescue beacons. An avalanche rescue beacon sends and receives electromagnetic field signals that travel in circular...
PBS
Pbs Learning Media: Tricking Hacker
In this video segment from Cyberchase, the CyberSquad must reclaim the Totally Rad Ring by measuring its radius to create a perfect duplicate.
BBC
Bbc: Bitesize: Maths: 2 D Shapes
Learn about the properties of 2-D shapes: circles, triangles, polygons, and quadrilaterals. Includes information, video, and examples about each, with games and quizzes for reinforcement.
Wolfram Research
Wolfram Math World: Pi
This site from Mathworld.com provides a detailed overview of pi. Content includes a diagram, an analysis of its value, how and when pi crops up in mathematics, historical references to pi, and more.
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...
Cuemath
Cuemath: What Is Pi?
Learn all about pi. This lesson targets what is pi, the pi symbol, the pi number, and the pi circle in the concept of what is pi. Check-out the interactive simulations to know more about the lesson and try your hand at solving a few...
National Council of Teachers of Mathematics
The Math Forum: Multicultural Math Fair: Srinivasa's Spheres
Straightforward lesson plan that introduces learners 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 and Spanish.