The change in speed each second, on the way up and down, is approximately 9.8 meters per second squared, which is the acceleration due to gravity.

Here's why:

* Gravity: The primary force acting on the ball is gravity. It constantly pulls the ball downwards.

* Acceleration: Acceleration is the rate of change of velocity. Since gravity pulls the ball downwards, it causes the ball to *slow down* on the way up and *speed up* on the way down.

* Constant Acceleration: The acceleration due to gravity is nearly constant near the Earth's surface. This means the ball's speed changes by approximately 9.8 meters per second every second.

Important Note: This assumes no air resistance. In reality, air resistance will have a small effect, making the acceleration slightly less than 9.8 m/s².