Final answer:
Projectile motion is an example of a trajectory in two dimensions caused by independent perpendicular motions. When a ball is thrown horizontally, it follows a curved path composed of two independent one-dimensional motions: horizontal and vertical.
Step-by-step explanation:
Projectile motion is an example of a trajectory in two dimensions caused by independent perpendicular motions. When a ball is thrown horizontally, it follows a curved path composed of two independent one-dimensional motions: horizontal and vertical. The key to analyzing projectile motion is to resolve it into motions along perpendicular directions. This is possible because the components of motion (horizontal and vertical) are independent of each other.