Force Systems – Definition Check for Coplanar Non-Concurrent Forces Evaluate the statement: “Forces that lie in the same plane but do not meet at a single point are called coplanar non-concurrent forces.”

Introduction / Context: Classifying force systems—concurrent, parallel, coplanar, spatial—guides which equilibrium equations and reduction methods to use. This item checks the precise wording of “coplanar non-concurrent forces.”

Given Data / Assumptions:

• A set of two or more forces acting on a rigid body.
• All lines of action lie within a single geometric plane.
• The lines of action do not intersect at one common point.

Concept / Approach: Terminology: Coplanar: lines of action in the same plane. Concurrent: lines of action meeting at a single point. Non-concurrent: no single intersection point common to all forces. Therefore, “coplanar non-concurrent forces” is the correct phrase for forces in a plane that are not all meeting at a common point.

Step-by-Step Solution: Check coplanarity: yes—same plane. Check concurrency: no—no single common intersection point. Therefore, the given statement matches the standard definition.

Verification / Alternative check: Examples include general 2D force systems on a rigid body with forces at different points and directions. Equilibrium requires ΣF_x = 0, ΣF_y = 0, and ΣM_O = 0 because moments cannot be reduced by concurrency.

Why Other Options Are Wrong: “Disagree”: contradicts standard definitions. “Agree only if they are parallel”: parallel forces are a subset; non-concurrency does not require parallelism. “Agree only if they are concurrent”: self-contradictory. “Agree only for two forces”: applies to any number of forces.

Common Pitfalls: Confusing “coplanar non-concurrent” with “parallel” or “concurrent”.

Final Answer: Agree