The rate at which falling objects accelerate over time remains constant in a vacuum, assuming no air resistance. This constant acceleration is due to gravity and is approximately 9.8 m/s² on Earth. This means that for every second an object falls, its speed increases by 9.8 meters per second.

However, in reality, air resistance plays a significant role. As an object falls, it encounters air molecules that create a force opposing its motion. This force increases as the object's speed increases.

Here's how air resistance affects acceleration:

* Initially: When an object starts falling, air resistance is minimal, and the acceleration is close to 9.8 m/s².

* As speed increases: The force of air resistance grows, opposing the force of gravity. This causes the net acceleration to decrease.

* Terminal velocity: Eventually, the force of air resistance becomes equal to the force of gravity. At this point, the object stops accelerating and falls at a constant speed called terminal velocity.

Therefore, the rate at which falling objects accelerate over time:

* In a vacuum: remains constant at 9.8 m/s².

* In air: decreases as the object's speed increases, eventually reaching terminal velocity where acceleration becomes zero.