Force Systems – Definition Check\nNon-coplanar concurrent forces are best described as forces that:

Introduction / Context:
Classifying force systems (concurrent, parallel, coplanar, non-coplanar) is fundamental in engineering mechanics for selecting the correct equilibrium equations and solution strategies.

Given Data / Assumptions:

• We are distinguishing between concurrency (meeting at a point) and coplanarity (lying in a single plane).

Concept / Approach:

• Concurrent forces: all lines of action intersect at a single point.
• Coplanar forces: all lines of action lie within the same geometric plane.
• Non-coplanar concurrent forces: concurrent but spanning three-dimensional space (not confined to one plane).

Step-by-Step Solution:
Identify concurrency: forces meet at one point. Check coplanarity: if lines do not lie on one plane, the system is non-coplanar. Thus: 'Meet at one point, but not in the same plane' is the correct description.

Verification / Alternative check:
Examples include three or more forces acting along directions in 3D that all intersect at a common joint, such as cable forces meeting at a node in space trusses.

Why Other Options Are Wrong:
Non-concurrent and non-coplanar: describes a general spatial system, not concurrent. Concurrent and coplanar: that is coplanar concurrent, not non-coplanar. Non-concurrent but coplanar: describes a different class. Always parallel: unrelated to concurrency or coplanarity.

Common Pitfalls:
Mixing up 'concurrent' with 'coplanar'; they are independent properties.

Final Answer:
Meet at one point, but their lines of action do not lie in the same plane