Plane Motion of a Rigid Body

Plane motion of a rigid body occurs when all body points move in planes parallel to a fixed plane. This type of motion is common in planar mechanisms.

Decomposition of motion

Plane motion can be represented as translation of a selected reference point combined with rotation about an axis perpendicular to the plane of motion. The choice of reference point does not change the physical motion but may simplify the analysis.

Velocities of points

The velocity of any point is obtained from the velocity of the reference point plus the relative velocity caused by body rotation. The instantaneous center of zero velocity is also useful for velocity analysis.

Accelerations of points

Point acceleration consists of the acceleration of the reference point and tangential and normal components associated with rotation. The instantaneous center used for velocities is not, in general, a universal center for acceleration calculations.