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# In reciprocating engines primary forces _________.a)Are completely balancedb)Are partially balancedc)Are balanced by secondary forcesd)Cannot be balancedCorrect answer is option 'B'. Can you explain this answer? Related Test: SSC JE (ME) Mock Test - 3

## SSC Question

 Learners World Jun 06, 2021
In the case of reciprocating masses, Primary forces are partially balanced. Because in the reciprocating masses, "the resultant forces" will be completely balanced, but "the resultant couple" won't be balanced; that is why we call reciprocating masses only partially balanced.
Since reciprocating mass cannot balance fully, partial balancing of the reciprocating mass is done while revolving masses can be balanced fully.
Primary unbalanced Force FP = mrω2cos2θ
Secondary unbalanced Force = FS = mrω2cos2θ/n
Effect of Partial Balancing of Reciprocating Parts
Reciprocating parts are only partially balanced. Due to this partial balancing of the reciprocating parts, there is an unbalanced primary force along the line of stroke and an unbalanced primary force perpendicular to the stroke line. The effect of an unbalanced primary force along the line of stroke is to produce;
• Variation in tractive force along the line of stroke
• Swaying couple