Question

moment of a couple
a couple is composed of two equal and opposite force - vectors separated by a perpendicular distance d.
in this activity, you will observe the following when either the force f or the perpendicular distance d is changed:

1. the couple magnitude increases or decreases

part a
as the forces f and - f reverse and their magnitude increases, how does the couple change?
the couple magnitude decreases, but its direction remains the same.
the couple magnitude decreases, and its direction reverses.
the couple magnitude increases, and its direction reverses.
the couple magnitude increases, but its direction remains the same.

Explanation:

The moment of a couple is given by $M = F\times d$. When the magnitude of forces $F$ and $-F$ increases (while the distance $d$ is constant), the product $F\times d$ increases, so the magnitude of the couple increases. Reversing the forces $F$ and $-F$ does not change the direction of the couple as the sense of the rotation (clock - wise or counter - clockwise) is determined by the relative orientation of the two forces which is still the same in terms of the overall rotation effect.

Answer:

The couple magnitude increases, but its direction remains the same.