Theory of Machine
When the nature of contact between the elements of a pair is such that one element can turn about the other by screw threads, the pair is known as a

Spherical pair
Screw pair
Sliding pair
Turning pair

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Theory of Machine
In a steam engine, the earlier cut-off with a simple slide valve may be obtained by increasing the steam lap and the angle of advance of the eccentric but keeping constant the travel and lead of the valve, this method will

Cause withdrawing or throttling of steam
Reduce length of effective stroke of piston
All of the listed here
Reduce maximum opening of port to steam

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