National Council of Teachers of Mathematics
The Math Forum: Elementary Geometry Circles
The Math Forum offers an archive of question and answer sessions on circles and how they relate to geometry.
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.
OER Commons
Oer Commons: Measuring Circles
Seventh graders will measure the circumference and diameter of round things in the classroom and discover the ratio pi. They will see that the ratio of a circle's circumference to its diameter can be used to solve for the circumference...
Cuemath
Cuemath: Area of a Circle
This mini-lesson explores the area of a circle. Provides a definition, examples, and practice questions with answers.
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...
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.
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.
PBS
Pbs Teachers: Building Columns
Explore different types of supports and the forces that act upon them. Investigate the best design of a column, including the role that size and dimensions play on its load capacity.
Alabama Learning Exchange
Alex: A Piece of Pi
This lesson plan uses graphing to help students understand that pi is a constant and is the slope of the line graphed on a circumference vs. diameter graph.This lesson plan was created as a result of the Girls Engaged in Math and Science...
Texas Instruments
Texas Instruments: Discovering Pi
Students will measure the circumference and diameter of round objects. They will send in their measurements through TI-Navigator and discover the relationship between the circumference and diameter.
Texas Instruments
Texas Instruments: Circle Around
In this activity, students compute the circumference and area of circles. They understand that the ratio of the circumference to the diameter is a value called pi. [Requires Adobe Reader.]
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.
Texas Instruments
Texas Instruments: Circles All Around
This activity provides students an opportunity to explore the relationship between the diameter of a circle and its circumference. [Requires Adobe Reader.]
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.
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.
Texas Instruments
Texas Instruments: Approximation of Pi
Students will measure the circumference and diameter of a variety of different circles. They will graph the class' values of (d,c) on the coordinate plane and use linear regression to approximate pi.
Texas Instruments
Texas Instruments: Predicting Pi
In this activity, students explore the use of linear measurement and calculators to discover the existence of pi, the constant ratio between the circumference and the diameter of a circle.
PBS
Pbs Mathline: Bubble Mania [Pdf]
Bubble Mania is a lesson plan that focuses on the concept of measurement as it applies to the diameter, circumference, and area in a bubble. Extension activities and connections, related worksheets, and additional resources are included.
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...
University of North Carolina
A Dictionary of Units of Measurement
This site contains an extensive list of various units of measurement known internationally and across several disciplines. Unit symbols are also included.
CK-12 Foundation
Ck 12: Geometry: Inscribed Angles in Circles
[Free Registration/Login may be required to access all resource tools.] This concept teaches students properties of inscribed angles and how to apply them.
CK-12 Foundation
Ck 12: Pi
[Free Registration/Login Required] Students will determine Pi by exploring the points on a circle. Click challenge me to answer practice questions and click learn more to watch a video.
CK-12 Foundation
Ck 12: Geometry: Arc Length
[Free Registration/Login may be required to access all resource tools.] This concept teaches students to find the length of an arc. Students examine guided notes, review guided practice, watch instructional videos and attempt practice...
Math Open Reference
Math Open Reference: Radius of a Circle
Learn about the radius of a circle with this useful reference guide. Provides a detailed definition, examples, and an interactive activity that enhances further explanation. Includes links to related topics.