Identify the incorrect statement from among the following:

Motion is classified by how a body's position changes over time. Periodic motion is any motion that repeats itself after a fixed, equal interval of time -- the shape of the path it follows is not restricted by that definition. Uniform circular motion (motion along a circle at constant speed) and ideal, undamped oscillatory motion (to and fro about a fixed mean position, not necessarily along a circular arc) are both examples of periodic motion, but they are different path shapes, not the same thing. Rectilinear motion, in contrast, means movement along a straight line.

Checking each statement against this classification: Earth completing one rotation about its axis every fixed time interval is a periodic motion. The rectilinear propagation of light -- its straight-line travel -- is rectilinear motion. A plucked sitar string vibrating to and fro about its equilibrium position is oscillatory motion.

• Earth's axial rotation repeats every fixed cycle, which is exactly periodic motion -- this statement is accurate.

• The rectilinear propagation of light -- its straight-line travel -- is exactly rectilinear motion -- this statement is accurate.

• A sitar string vibrating to and fro about its equilibrium position is exactly oscillatory motion -- this statement is accurate.

• “All periodic motions are circular motions” overreaches: periodicity only needs equal-time repetition, not a circular path -- an idealized vibrating string, a swinging pendulum, and a bouncing spring are all periodic yet trace no circle, so this generalisation is false.

Because periodicity depends only on regular repetition in time and places no requirement on the shape of the path, the claim equating every periodic motion with circular motion is the incorrect statement here.