A representation of what [math]\pi[/math] is, its relation to the unit of angle measure called radians, and the difference between radians and degrees.[br][br]In this worksheet, the gridlines are separated by r units, where r is the radius of the two circles. d represents the distance the center of the circle has moved. As you change d by dragging the slider or by directly inputting the value at the bottom left, the blue segment gets wrapped around the circle. (Note: d also has units of r.)