Here's why:
* Gravity: The only force acting on the ball throughout its flight is gravity. Gravity always pulls objects towards the center of the Earth, which is downward.
* Velocity at the Top: At the very top of its trajectory, the ball momentarily has zero vertical velocity. However, the ball's velocity is about to change direction from upward to downward.
* Acceleration's Role: Acceleration is the rate of change of velocity. Since the ball's velocity is changing from upward to downward, its acceleration must be pointing downward.
Important Note: Even though the ball momentarily stops at the top, gravity continues to act on it, causing it to accelerate downward and begin its descent.
