# Couple-Moment of couple is free vector, resultant of a couple is always zero

Q.  Which of the following statements is false about forces/couple?
- Published on 21 Sep 15

a. Moment of couple is free vector
b. Resultant and equilibrant are equal in magnitude and direction
c. Resultant of a couple is always zero
d. Parallelogram law is to be proved experimentally

ANSWER: Resultant and equilibrant are equal in magnitude and direction

#### Discussion

• Sravanthi   -Posted on 14 Dec 15
- Parallelogram law: When two coplanar concurrent forces acting on a point are represented in magnitude and direction by two adjacent sides of a parallelogram, resultant of these forces is represented in magnitude and direction by the diagonal of this parallelogram which passes through the intersection of two forces. Therefore, this law is impossible to be proved mathematically and hence is proved experimentally. This law is applicable to concurrent forces.

- Couple is formed due to two unlike, non-collinear forces which have same magnitude. Resultant of a couple is zero

- Moment of couple is considered as a free vector as it can be applied at any point. The results obtained by a couple system remains the same even if the origin is shifted. Hence, it is independent of the origin and called as a free vector.

- Equilibrant force is equal and opposite to that of resultant force. This causes an object to be in equilibrium.

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