Final answer:
Gravity is always pulling objects towards Earth, leading to a constant downward acceleration for a bouncing ball even as it moves upwards. The constant negative value in a graph of vertical acceleration versus time for a ball in free fall represents this unchanging gravitational influence.
Step-by-step explanation:
When a ball bounces up, the acceleration points down due to the force of gravity. The important thing to understand is that gravity is always acting on the ball, pulling it toward the Earth, regardless of the direction the ball is moving. As the ball bounces up and away from the Earth, it slows down due to the gravitational pull, which means its velocity is decreasing; therefore, the acceleration is opposite in direction to the velocity. Even when the ball is moving upwards, gravity continues to exert a constant downward force on it, leading to a constant downward acceleration.
In an experiment where a ball is launched with an initial horizontal velocity and follows a parabolic trajectory, the graph of the ball's vertical acceleration versus time would show a negative constant value, representing gravity's unchanging influence. During both the ascent and descent, this acceleration remains constantly negative because gravity is consistently pulling the ball downward, which is considered the negative direction in this context.
It's significant to note that when a ball bounces or is in any form of free fall, it's being affected by gravity both on its way up and on its way down. This is what causes the ball's vertical velocity to decrease on the way up, come to a brief stop at the apex of its path, and then increase in the negative direction on its way down, with its acceleration always pointed downward.