The speed of an object in free fall changes by 9.8 meters per second (m/s) every second. This is due to the acceleration due to gravity, which is approximately 9.8 m/s².

Here's a breakdown:

* Acceleration: Acceleration is the rate of change of velocity. In free fall, the only force acting on the object is gravity, causing it to accelerate downwards.

* Gravity's Influence: The acceleration due to gravity (g) is approximately 9.8 m/s². This means that for every second an object is in free fall, its velocity increases by 9.8 m/s.

Example:

* If an object is dropped from rest, its initial velocity is 0 m/s.

* After 1 second, its velocity will be 9.8 m/s.

* After 2 seconds, its velocity will be 19.6 m/s (9.8 m/s + 9.8 m/s).

Important Note: This assumes no air resistance. In reality, air resistance will slow down the object's acceleration, and its speed will not increase by 9.8 m/s every second.