Parts of the Circle for Fifth Grade Math
Circles are everywhere, from the tires on cars to the pans on the stovetop and the pie plates in the oven. Children are taught early on to identify circles, but it is not until later that they are taught the parts of a circle and the measurements related to them. Knowing the components that make up a circle and how to make calculations using a circle ensures one can find the right tires for a car or roll a piecrust that will fit in a pie plate. These skills are also crucial for passing math class.
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Radius
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The radius of a circle is the distance from the circle's center point to any point on the circle. This is an important number in geometry because it can be used to determine a circle's diameter, circumference and area. Because of the circle's shape, the radius can be drawn in anywhere in the center of the circle.
Diameter
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Officially, the diameter of a circle is defined as the length of a straight line through the center of a circle and touching two points on its edge, but it's easier to remember that the diameter is twice the measurement of the radius. It is the longest distance across the circle. If the diameter of a circle is known, dividing by two will yield the radius.
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Circumference
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A circle's circumference is the distance around the circle. To determine the circumference of a given circle, multiply the diameter by pi, or multiply the radius by 2 then multiply by pi. Pi is a mathematical constant symbolized by the Greek letter π and is approximately 3.14159.
Area
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The area of a circle is a measurement of the space inside the circle's circumference. Regardless of the units used to measure area, it is always expressed as a square of the unit to indicate it is a two-dimensional measurement. For example, if the diameter is given in inches, the area would be measured in square inches.
Chord
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A chord is any straight line that connects two points on the circle. By definition, the diameter of a circle is a chord. It is also the longest chord for any given circle. There are two mathematical formulas that can determine the length of a chord depending on the information that is known. If a chord length and one other piece of information is provided, it is possible to determine the radius length using trigonometry.
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References
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