Final answer:
The ball's upward motion slows due to constant downward acceleration until velocity is zero at the peak. It then accelerates downward, increasing velocity in the opposite direction, with gravity's acceleration being constant and in the same direction throughout the motion.
Step-by-step explanation:
When a ball is tossed straight up into the air, its motion can be described using the concepts of acceleration, velocity, frame of reference, and displacement. Upon release, the ball initially has an upward velocity that decreases over time because it is under the influence of gravity, which acts as a constant downward acceleration. The frame of reference could be considered the environment in which the ball is moving, typically earth-centered for our common experiences.
As the ball ascends, its velocity reduces until it reaches its peak, where its velocity is zero. The displacement here is the maximum height achieved relative to the point of release. Once the ball begins its descent, it accelerates downwards, increasing its velocity in the opposite direction compared to the ascent. Throughout this entire motion, the acceleration due to gravity remains constant and in the same direction (towards the earth's center). The entire path of the motion of the ball, both upwards and downwards, describes its displacement.
Therefore, the acceleration of gravity has the same sign on the way up as on the way down because it always acts in the direction of the earth's center, which is considered a negative direction in this context.