# 5.10 - Circles

The student will

• identify and describe the diameter, radius, chord, and circumference of a circle.

### BIG IDEAS

• So that I can design circular objects such as camera lenses, pizzas, tires, ferris wheels, rings, steering wheels, cakes, pies, buttons, satellites, etc.
• So that scientists studying the planets can use circumference of the planets to help compare the planets to their relative sizes and to each other
• So that I can use my knowledge of radius and diameter to find the area of a circle
• So that I can use my knowledge of radius and diameter to find the circumference of a circle
• So that an architect can precisely design arcs or buildings with a circular structure

### UNDERSTANDING THE STANDARD

• A circle is a set of points in a plane that are the same distance from a point called the center.
• A chord is a line segment connecting any two points on a circle. A chord may or may not go through the center of a circle.  The diameter is the longest chord of a circle.
• A diameter is a chord that goes through the center of a circle. The length of the diameter of a circle is twice the length of the radius.
• A radius is a line segment joining the center of a circle to any point on the circle. Two radii end-to-end form a diameter of a circle.
• Circumference is the distance around or “perimeter” of a circle.  An approximation for circumference is about three times the diameter of a circle.  An approximation for circumference is about six times the radius of a circle.

### ESSENTIALS

The student will use problem solving, mathematical communication, mathematical reasoning, connections, and representations to

• Identify and describe the diameter, radius, chord, and circumference of a circle.
• Investigate and describe the relationship between