Definition

Rigid motion
A motion is said to be rigid motion, if it preserves distance. That is for P ≠ Q,
PQ = P'Q' where P' and Q' are the images of P and Q, respectively. Otherwise it is said to be non-rigid motion.

A transformation is said to be an identity transformation, if the image of every point is itself. For example, if an object is rotated 360^o it is an identity transformation.

Note: Rigid motion carries any plane figure to a congruent plane figure, i.e., it carries triangles to congruent triangles, rectangles to congruent rectangles, etc.

An identity transformation is a rigid motion.

In this unit two different types of rigid motions are presented.