Definition of a Couple in Physics

Steps:

• Identify that a couple involves two forces of equal magnitude and opposite direction.
• Confirm the forces are parallel but not collinear, resulting in zero net force.
• Determine the effect: no linear acceleration (translation) but nonzero torque.
• Match this to the option describing rotational motion without translation.

Why A is correct:

• A couple is defined as two equal and opposite parallel forces that produce a pure torque, causing rotation without net translation, per Newton's laws and torque formula τ = r × F.

Why the others are wrong:

• B: Couples produce no translation due to zero net force, not translational motion.
• C: Forces in a couple act in opposite directions, not the same; phrasing is also incorrect.
• D: Same-direction forces produce net force and translation, not a couple's rotation.

Final answer: A