What does projectile motion refer to?

Projectile motion refers to the motion of an object that is launched into the air and is subject to the influence of gravity and, typically, air resistance. The characteristic of projectile motion is that it follows a curved path, specifically a parabolic trajectory, when observed from a fixed frame of reference, such as the Earth's surface. This curvilinear motion results from the combination of the initial velocity of the object and the acceleration due to gravity acting downward, which distorts the straight-line path into a curve.

In this context, the curved path described in the correct answer captures the essential nature of projectile motion, where the effects of gravity cause the object to ascend to a peak height before descending back to the ground. Understanding this is fundamental as it differentiates projectile motion from linear motions, where gravity's influence is not a factor, or such other conditions listed in the other options.