Q: Is the edge of a circle with an infinite radius curved or straight?
http://www.askamathematician.com/2011/04/q-is-the-edge-of-a-circle-with-an-infinite-radius-curved-or-straight/
"Nail down the edge of a circle. As the center gets farther and farther away, the radius gets larger, and the curvature gets smaller. When the "circle is centered at infinity" the curvature drops to zero, and the edge becomes a straight line (black)."
http://www.askamathematician.com/2011/04/q-is-the-edge-of-a-circle-with-an-infinite-radius-curved-or-straight/
"Nail down the edge of a circle. As the center gets farther and farther away, the radius gets larger, and the curvature gets smaller. When the "circle is centered at infinity" the curvature drops to zero, and the edge becomes a straight line (black)."