Final answer:
What is achieved when acceleration due to gravity is balanced by air resistance is terminal velocity, where an object falls at a constant speed without further acceleration.
Step-by-step explanation:
When acceleration due to gravity is balanced by air resistance, an object achieves a state called terminal velocity. This is the constant speed at which the force of gravity is exactly balanced by the upwards force of air resistance, resulting in no further acceleration. This phenomenon explains why a feather falls more slowly than a hammer in air; the feather reaches terminal velocity quickly due to a greater surface area relative to its mass, while the hammer, having a smaller surface area relative to its mass, falls faster until it too reaches its terminal velocity.
If air resistance is negligible, objects would continuously accelerate due to gravity until they hit the ground. This is illustrated by the uniform acceleration experienced by all objects in a vacuum, regardless of mass, as demonstrated by astronaut David R. Scott on the Moon, where there is no atmosphere to provide air resistance and the acceleration due to gravity is only 1.67 m/s².