Final answer:
The interaction between centripetal force and inertia causes circular motion, where centripetal force is required to alter the straight-line path that inertia would otherwise dictate.
Step-by-step explanation:
The interaction between centripetal force and inertia leads to circular motion. When an object is in circular motion, its velocity is constant in magnitude, but since the direction is continually changing, the object experiences an acceleration known as centripetal acceleration. This acceleration is due to the centripetal force, which acts towards the center of the circular path. This force can result from various sources such as tension, gravity, or friction, and it keeps the object moving in a circle rather than in a straight line which would be the case if inertia alone were at work.
According to Newton's first law, an object in motion continues to move in a straight line unless acted upon by an external force. The centripetal force is that external force which directs the object towards the center, causing a circular path. If this force suddenly stops, such as when a string breaks on a swinging yoyo, the object will move in a straight line tangent to the circle at the point where the force ceases, due to inertia.
Therefore, the correct answer to the question is a. Circular motion. This type of motion is evidenced in various examples, including cars rounding a curve where the friction acts as the centripetal force, and amusement park rides where tension forces maintain circular paths.