Definition of a Couple in Physics

Steps:

• Recall that a couple consists of two equal and opposite forces acting on an object.
• Determine the net force: since forces are equal and opposite, resultant force is zero.
• Analyze the effect: the forces create a torque, causing rotation without translation.
• Match to options: identify the one describing rotation only, with no net force.

Why D is correct:

• A couple produces pure rotation because the two equal, opposite, non-collinear forces yield zero net force but non-zero torque (τ = r × F).

Why the others are wrong:

• A: Couples act at different points, not the center of gravity, to avoid net force.
• B: Forces in a couple act in opposite directions, not the same.
• C: Couples produce no resultant force, only torque for rotation.

Final answer: D