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regardless  of      external  forces  exerted  on  it.  In  classical  mechanics  a
                  rigid body is usually considered as a continuous mass distribution
                           In  mechanics,  degrees  of  freedom  (DOF)  is  the  number  of
                  parameters  that  define  the  configuration  of  a  mechanical  system.  The

                  degrees of freedom of a body is the number of independent parameters
                  that  define  the  displacement  and  deformation  of  the  body.  This  is  a
                  fundamental  concept  relating  to  the  systems  of  moving  bodies  in

                  mechanical  engineering,  aeronautical  engineering,  robotics,  and
                  structural engineering.
                          The position of a single car  moving along a track has one degree of
                  freedom, because the position of the car is defined by the distance along

                  the track. A train of rigid cars connected by hinges to an engine still has
                  only one degree of freedom because the positions of the cars behind the
                  engine are constrained by the shape of the track.

                           An automobile can be considered to be a rigid body travelling on a
                  plane (a flat, two-dimensional space). This body has three independent
                  degrees of freedom consisting of two components of translation and one

                  angle  of  rotation.  Skidding  or  drifting  is  a  good  example  of  an
                  automobile's three independent degrees of freedom.
                           The  position  of  a  rigid  body  in  space  is  defined  by  three

                  components  of  translation  and  three  components  of  rotation,  which
                  means that it has six  degrees
                           The  motion  of  absolutely  rigid  body  includes  the  motion  of  the
                  center of mass and  rotations around axis that pass through the center of

                  mass. Translation motion of absolutely rigid  body is such motion when
                  any line closely connected with the body moves parallel to the initial
                  position

                          All  points  of an  absolutely  rigid body  at  the  same time pass  the
                  same distances, hence, the velocities v and accelerations a for all points
                  of  the  absolutely  rigid  body  are  equal.  Therefore  consideration  of
                  translation motion of the absolutely rigid body reduces to the study of

                  motion of its arbitrary point (for example, the center of mass).
                        Consider a rigid body of  triangle form as shown in fig.1.11. First
                  position  a  illustrates translation motion  when  this  body moves  parallel

                  in three direction , three axis OX, OY, OZ     and therefore  three  are three
                  degrees of freedom on translation motion
                     .







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