Here's why:

* Gravity: The object is constantly being pulled downwards by gravity.

* Upward Motion: As the object moves upwards, its velocity decreases due to gravity's opposition.

* Highest Point: At the very top, the object momentarily stops moving upwards. This is because gravity has completely negated its initial upward velocity.

* Downward Motion: At this instant, the object begins to fall back down, meaning its velocity is now in the downward direction.

Key Points:

* Velocity is a vector quantity, meaning it has both magnitude (speed) and direction.

* While the object's velocity is zero at the highest point, its acceleration is not. It's still accelerating downwards due to gravity.