Answer is:
permit relative motion
Explanation:
The two links or elements of a machine, when in contact with each other, are said to form a pair. If the relative motion between them is completely or successfully constrained (i.e. in a definite direction), the pair is known as kinematic pair.
Answer is:
Ball and socket joint
Explanation:
When the two elements of a pair are connected in such a way that one element (with spherical shape) turn or swivels about the other fixed element, the pair formed is called a spherical pair. The ball and socket joint, attachment of a car mirror, pen stand etc., are the examples of a spherical pair.
