Final answer:
A force will not produce a moment about an axis in 3D equilibrium if it passes through the axis, due to there being no perpendicular component. Equal and opposite forces act on a point in equilibrium. Essential physics concepts highlight that force perpendicularity is required for a torque.
Step-by-step explanation:
In 3D equilibrium, a force will not cause a moment about an axis if it passes through the axis. This is because the line of action of the force intersects with the axis, resulting in zero perpendicular distance to the axis, which is a necessary component for a torque to exist. The torque (τ) is the product of the force (F) and the perpendicular distance (d) from the axis to the line of action of the force, formulated as τ = F * d. If this distance is zero, the torque is also zero.
A point acted on by two forces in equilibrium have equal magnitudes but opposite directions. This is in accordance with Newton's third law of motion which states that for every action, there is an equal and opposite reaction.
Under the first condition for equilibrium, such as in statics problems, net torque must be zero to maintain equilibrium. The Essential Knowledge 3.F.1 from physics curriculums emphasizes that only the force component perpendicular to the axis causes a torque, corroborating the answer to the initial question.