Friction provides the centripetal force for the turn

Steps:

• Circular motion requires a centripetal force directed toward the turn's center.
• Leaning tilts the motorcycle, aligning the net force (friction and gravity components) inward.
• Friction between tires and road supplies this horizontal inward force.
• Without friction, the motorcycle would slide straight instead of turning.

Why A is correct:

• Friction acts tangentially to the road surface, providing the necessary centripetal force $F_c = \frac{mv^2}{r}$ for curved motion.

Why the others are wrong:

• B (gravity): Pulls downward, contributing to lean stability but not the horizontal turn force.
• C (centrifugal force): Fictitious outward force in rotating frame; real turns result from inward forces.
• D (normal force): Perpendicular to road, supports weight vertically but lacks horizontal component for turning.

Final answer: A