Here's why:

* Free Fall: This means the object is only under the influence of gravity. There's no air resistance or other forces affecting its motion.

* Gravity: This is the force of attraction between any two objects with mass. The Earth has a large mass, so it exerts a strong gravitational pull on objects near its surface, causing them to fall towards it.

Important Note: While gravity is the only force *acting* on an object in free fall, the object will experience other forces like air resistance (drag) in real-world scenarios. However, these forces are usually considered negligible in idealized free fall scenarios.