Lesson 11 Preview: Unrolling a Circle
When a bike tire turns one revolution the bike travels a distance equal to the circumference of the tire. If the tire has a radius of 1 unit, then its circumference is .
As the tire rolls in this visualization, the circumference (shown in red) unrolls and sticks to the ground. The length of that unrolled piece of the circumference is the arc length corresponding to a certain fraction of a revolution.