* Velocity: When you throw the ball upwards, its velocity is initially positive (let's say upwards is the positive direction).

* Acceleration: However, gravity acts constantly downwards, pulling the ball back towards the Earth. This means the ball's acceleration is *negative* (opposite to the initial velocity).

As the ball travels upwards, its velocity decreases due to the downward acceleration. At the peak of its trajectory, the ball's velocity momentarily becomes zero before it starts falling back down. During the descent, the velocity is now downwards (negative) but the acceleration remains constant and downwards (negative), meaning they are still in opposite directions.