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1. Translation. This type of motion occurs when a line in the
body remains parallel to its original orientation throughout the motion.
When the paths of motion for any two points on the body are parallel
lines, the motion is called rectilinear translation, Fig. 2-16,a. If the
paths of motion are along curved lines which are equidistant, the
motion is called curvilinear translation, Fig. 2-16,b.
2. Rotation about a fixed axis. When a rigid body rotates about a
fixed axis, all the particles of the body, except those which lie on the
axis of rotation, move along circular paths, Fig. 2-16,c.
3. General plane motion. When a body is subjected to general
plane motion, it undergoes a combination of translation and rotation,
Fig. 2-16,d. The translation occurs within a reference plane, and the
rotation occurs about an axis perpendicular to the reference plane.
In the following sections we will consider each of these motions
in detail. Examples of bodies undergoing these motions are shown in
Fig. 2-17.

Fig 2- 17.

Analysis of the plane motion of rigid bodies is accomplished
either by directly calculating the absolute displacements and their time
derivatives from the geometry involved or by utilizing the principles
of relative motion. Each method is important and useful and will be
covered in turn in the articles which follow.

47 Translation Motion

Translation motion is defined as any motion in which every line
in the body remains parallel to its original position at all times. In
translation there is no rotation of any line in the body.

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