# Circles

## Circumference and Area of Circles: Labeling Parts of a Circle

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Radius, diameter, center, and circumference--all are parts of a circle. Let's go through each and make sure we understand how they are defined.

## Distance Difference

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Using circumference, this video measures the total distance traveled by two carousel riders after the carousel has rotated 10 times. Regents Review materials are designed to help high school students prepare for New York State's Regents exams.

## Formulas: Area of a Circle

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Learning about formulas will help you develop a strong foundation for your work in geometry. This video explains the formula for finding the area of a circle.

This video segment is from the GED Connection Formulas video.

## Concentric Circles

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In this video you’ll discover how using concentric circles can help you determine how much paint is needed to cover the deck of a carousel. Regents Review materials are designed to help high school students prepare for New York State's Regents exams.

## Formulas: Circumference

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The distance around a circle is called the circumference. You can find the circumference of any circle by using the formula C = 2πr. Watch the video to learn about the formula for circumference.

This video segment is from the GED Connection Formulas video.

## Urban Planner

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A professor and graduate student talk about the use of math and technology in city planning.

## Zombies and Calculus, Part 2

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Learn about tangent vectors in this video from NOVA Digital. In this hypothetical world, zombies always move straight toward humans. This means that the tangent vector of a zombie's path points at the intended target. However, when the human moves, the zombie's tangent vector points to where the human is at that instant, not to where the human is going. The zombie is not smart enough to move toward where the human will be. Therefore, the zombie takes a longer path, giving the human the chance to get away. If the human moves faster than the zombies in a circular path, multiple zombies will eventually converge on a smaller circular path that follows the human's path.

## Sir Cumference and the Dragon of Pi

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When Sir Cumference drinks a potion which turns him into a dragon, his son Radius searches for the magic number known as pi which will restore him to his former shape.

Keywords: king, heir, geometry, math, quest, puzzles, dragon

## Sir Cumference and the First Round Table

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What would you do if the neighboring kingdom were threatening war? Naturally, you'd call your strongest and bravest knights together to come up with a solution. But when your conference table causes more problems than the threat of your enemy, you need expert help. Enter Sir Cumference, his wife Lady Di of Ameter, and their son Radius. With the help of the carpenter, Geo of Metry, this sharp-minded team designs the perfect table conducive to discussing the perfect peace plan. Thanks to Sir Cumference and the First Round Table, even the most hesitant will be romancing math.

## Sir Cumference and the Isle of Immeter

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When young Per visits her uncle Sir Cumference, aunt Lady Di of Ameter, and her cousin Radius, they teach her how to play Inners and Edges. After Per finds a clue linking the game to the mysterious castle of the Countess Areana, she and Radius sail to the island of Immeter. There, they have to decipher cryptic clues while avoiding a sea serpent. To unlock the island's secret, Per has to figure out how to find the perimeter and area of a circle. Only then can she become Per of Immeter.