What position variable in circular motion is analogous to the number line position variable in rectilinear motion?

Rectilinear motion and circular motion are similar in that, in their strict forms, they comprise single degree-of-freedom systems. As the position of a rectilinear movement can be noted with the location along the number lone, the position of a body undergoing circular motion is generally denoted by the angle (represented by the Greek letter theta) in either radians or degrees.

I'm not sure what your asking buddy.. but i know that you can weld two peices of steel by pure force and pressure.

  concave means having an outline or surface that curves inward like the interior of a circle or sphere. so the mirror curves inward.