# Surface area of a curve revolved around the polar axis

"Find the area of the surface obtained by revolving the curve $r=\cos \theta$, $0 < \theta < \pi$ about the polar axis. What is the arc length of this curve?"

I know how to find the arc length, but I'm not sure what it means to revolve around the polar axis.

Hint...the curve is a circle of radius $\frac 12$