Moment of a Couple

Learning Goal:

To be able to calculate couple moments.

A couple is defined as two parallel forces, separated by a

distance, that have equal magnitudes but opposite

directions. A couple only produces a rotation in a

specified direction. The moment produced by a couple is

called a couple moment.

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Part A

MA,MB,MR =

As shown, a submarine hatch door is to be opened by applying two oppositely oriented forces of equal magnitude F = 170 N at points A

and B on the hatch door wheel. The radii of the wheel's inner and outer rings are r1 0.550 m and r2 = 0.130 m, respectively. (Figure 1)

Calculate the moments MA and MB about point D for the forces applied at points A and B. Then, determine the resulting couple moment

MR. Assume that a positive moment produces a counterclockwise rotation whereas a negative moment produces a clockwise rotation.

Express your answers numerically in newton-meters to three significant figures separated by commas.

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