# Helical pair has degree of freedom_____.

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Helical pair has degree of freedom_____.
1. 1
2. 2
3. 3
4. 4

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Correct Answer - Option 1 : 1
Explanation:

Kinematic pair:

A kinematic pair or simply a pair is a joint of two links having relative motion between them.

Kinematics pair can be classified according to:

1. Nature of contact
2. Nature of relative motion
3. Nature of mechanical constraint

Helical Pair (H-pair): A helical pair has one degree of freedom and permits rotational and translational motion. These motions are, however, related by the pitch value of the helical pair. A helical pair is often called a screw pair. Example: Motion between the bolt and fixed nut

1) Kinematic pairs according to Nature of Contact:

 Lower pair Higher pair A pair of links having surface or area contact between the members is known as a lower pair. The contact surface of the two links is similar. When a pair has a point or line contact between the links, it is known as a higher pair. The contact surface of the two links is dissimilar. E.g Nut turning on a screw, shaft rotating in a bearing, all pairs of slider-crank mechanism, universal joint, etc. E.g Wheel rolling on a surface, cam and follower pair, tooth gears, ball and roller bearing etc.

2) Kinematic pair according to nature of relative motion:

 Sliding pair When two links are so connected that one is constrained to have sliding motion relative to another. Eg. crosshead and guide, rectangular rod in a rectangular hole in a prism. Turning pair When two links are so connected that one is constrained to turn or revolve about a fixed axis of another. Eg. crankshaft turning in a bearing. Rolling pair Two elements of a pair are connected in such a way that one rolls over another fixed link.  Eg. Ball and roller bearings, rolling wheel on a flat surface, etc. Screw pair If two mating links have a turning as well as sliding motion between them, they form a screw pair. this is achieved by cutting matching threads on the two links. Eg. the lead screw and the nut of a lathe is a screw pair and a bolt with nut Spherical pair Two elements of a pair are connected in such a way that one element (with the spherical shape) turns or swivels about the other fixed element.  Eg. the ball and socket joint, attachment of a car mirror, pen stand, etc

3) According to the nature of mechanical constraint:

 Closed pair Unclosed pair When the elements of a pair are held together mechanically they constitute a closed pair. When two links of a pair are in contact either due to force of gravity or some spring action, they constitute an unclosed pair.