Principle of transmissibility of forces\n\nAccording to the principle of transmissibility, when a force acts upon a rigid body, its external effect (on overall equilibrium and motion) is:

Introduction / Context:
The principle of transmissibility simplifies force systems in rigid-body mechanics. It allows engineers to shift a force along its line of action without changing the body's external effects.

Given Data / Assumptions:

• The body is treated as rigid (no deformation effects considered).
• We consider only external effects such as overall equilibrium and motion, not internal stress distribution.

Concept / Approach:
The principle states: a force may be applied at any point along its line of action to a rigid body and will produce the same external effect. Internal stresses can differ, but the net force and moment about any point remain unchanged.

Step-by-Step Solution:

Verification / Alternative check:
Compute moments about any reference: moving the force along its own line keeps the perpendicular distance to that line the same, so resultant moment contributions are unchanged.

Why Other Options Are Wrong:

• Different at different points: Contradicts the principle for rigid bodies.
• Minimum/Maximum at CG: Not a general rule; effect depends on line of action, not simply proximity to CG.
• Zero on a parallel line: Shifting to a parallel but distinct line requires an added couple (equivalent force–couple system), changing external effects.

Common Pitfalls:
Confusing internal stresses (which do change) with external effects (which do not, for a rigid body).

Final Answer:
same at every point on its line of action