Principle of transmissibility of a force (rigid-body mechanics) According to the principle of transmissibility, the mechanical effect of a force on a rigid body remains what when the point of application is shifted along its line of action?

Introduction / Context:
The principle of transmissibility enables engineers to move a force along its own line of action without changing the external effect on a rigid body. This simplifies free-body diagrams and statics reductions, provided the body can be treated as perfectly rigid.

Given Data / Assumptions:

• Rigid-body assumption (no deformation-induced stress redistribution considered).
• Same line of action maintained during shifting.
• Moments from couples are treated separately.

Concept / Approach:

Forces that share the same line of action are statically equivalent in their external effect on a rigid body. Moving the point of application along the line of action does not change the resultant force or net moment about any external point; internal stress distributions can differ, but statics problems focus on external effects.

Step-by-Step Solution:

Verification / Alternative check:

Compare net force and net moment before and after shifting: both are identical; hence, external equilibrium and reactions are unchanged.

Why Other Options Are Wrong:

(a) and (d) incorrectly tie effectiveness to C.G.; (b) contradicts the principle; (e) is inapplicable.

Common Pitfalls:

Applying transmissibility to deformable bodies where internal effects matter; confusing shifting along the line of action with moving off the line, which introduces a couple.

Final Answer:

The same at every point on its line of action (unchanged effect)