Here's why:

* Gravity: The primary force acting on a falling object is gravity, pulling it downward.

* Air Resistance: As the object falls through the air, it collides with air molecules. This collision creates a force opposing the object's motion, called air resistance or drag. The faster the object falls, the greater the air resistance.

Important Note: Air resistance is a significant factor in the object's overall motion. If there were no air resistance, all objects would fall at the same rate, regardless of their mass (as demonstrated in a vacuum). However, in the real world, air resistance plays a crucial role, especially for objects with large surface areas or light weights.