LINK AND PAIRS

LINK -: Every part of a machine having motion re-lative to some other part is called link. In other words a link is defined as a rigid body having two or more pairing elements which connect it to the other bodies for the purpose of transmitting force or motion.                                                                      In every machine, at least one link either occupies a fixed position . And also carries the machine as a whole along with it during motion. A example of link is bicycle chain silver necklace etc.

PAIRS -:                                                                                   In a machine when two links or elements are contact ecah other ,they form a pair. If the relative motion between them is completely or successfully constrained in a definite direction, then the pair is known as Kinematic pair.

LOWER PAIR-:                                                                     The Lower pairs are those in which two elements have surface contact and relative motion takes place between them, e.g. nut and the screw, the universal joint used to connect two propeller shafts. A lower pair is an ideal joint that constrains contact between a surface in moving body to a corresponding surface in the fixed body.

HIGHER PAIR-:                                                                     The higher pairs have the line or point contact and pair is forced-closed in order to provide completely constrained motion. Two ele-ments held together mechanically from a closed pair and those not held together mechanically from unclosed pair.