Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

10.3 Moment, Torque —Force Acting at a Distance 265

a^

MD 1 100 N 21 0.35 m 2  1 100 N 21 0.25 m 2 10 N#m



a^

MC 1 100 N 21 0.25 m 2  1 100 N 21 0.15 m 2 10 N#m



a^

MB 1 100 N 21 10 m 2  1 100 N 2102 10 N#m



a^

MA 1 100 N 2102  1 100 N 21 0.1 m 2 10 N#m



0.1 m

A

C

D

B

100 N

100 N

0.1 m

0.15 m

■Figure 10.14 A schematic diagram for Example 10.6.

Referring to Example 10.6, note that two forces that are equal in magnitude and oppo-

site in direction (not having the same line of action) constitutea couple. As you can see from

the results of this example, the moment created by a couple is equal to the magnitude of either

force times the perpendicular distance between the line of action of the forces involved. Also,

note for this problem, we assigned a positive sign to clockwise rotation. Since the sum of the

moments has a positive value, the overall tendency of forces is to turn the object clockwise.

External Force, Internal Force, Reaction Force

We explained the concept of external force and moment previously. Let us now discuss the con-

cept of internal and reaction forces. When an object is subjected to an external force, internal

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