Here's why:

* Free-fall: This means the object is only under the influence of gravity. No other forces, like air resistance, are acting on it.

* Acceleration due to gravity (g): This is the constant acceleration experienced by objects near the Earth's surface due to the gravitational pull of the Earth. Its value is approximately 9.8 m/s².

Therefore, in free-fall, the acceleration of the object is always 9.8 m/s² (or approximately) directed downwards, regardless of the object's mass.

Important Note: In reality, air resistance can affect free-fall, but it is often negligible for objects with small surface areas and high densities. In those cases, the object's acceleration is very close to 9.8 m/s².