Here's why:
* Gravity acts consistently: The only force acting on a projectile in the vertical direction is gravity. This force pulls the projectile downwards at a constant rate, resulting in a constant downward acceleration.
* Zero velocity doesn't change acceleration: The fact that the vertical component of the velocity vector is zero at a specific instant doesn't change the acceleration due to gravity. It simply means the projectile is momentarily stopped in the vertical direction before it starts moving downwards again.
Think of it this way:
Imagine throwing a ball straight up. At the peak of its trajectory, its vertical velocity is zero for an instant. However, it still experiences the downward force of gravity, causing it to accelerate downwards and begin falling.
Important Note: The horizontal component of the projectile's velocity remains constant throughout its flight, assuming we ignore air resistance.
