# When the relative motion between two elements is completely or successfully constrained, then these two elements form a-

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When the relative motion between two elements is completely or successfully constrained, then these two elements form a-
1. Mechanism
2. Machine
3. Kinematic pair
4. Kinematic chain

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Correct Answer - Option 3 : Kinematic pair

Explanation:

Kinematic pair

• 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.

Kinematic chain

• A kinematic chain may be defined as a combination of kinematic pairs, joined in such a way that each link forms a part of two pairs
• For example, the crankshaft of an engine forms a kinematic pair with the bearings which are fixed in a pair, the connecting rod with the crank forms a second kinematic pair, the piston with the connecting rod forms a third pair and the piston with the cylinder forms the fourth pair. The total combination of these links is a kinematic chain.

Mechanism and Inversion

• When one of the links of a kinematic chain is fixed, the chain is known as mechanism
• It may be used for transmitting or transforming motion e.g. engine indicators, typewriters, etc.
• A mechanism with four links is known as a simple mechanism, and the mechanism with more than four links is known as compound mechanism
• We can obtain as many mechanisms as the number of links in the kinematic chain by fixing, in turn, different links in a kinematic chain.
• This method of obtaining different mechanisms by fixing different links in a kinematic chain is known as inversion of the mechanism.