Here's why:

* Gravity's Constant Pull: Gravity exerts the same force on all objects, regardless of their mass or size. This force pulls objects towards the center of the Earth.

* Acceleration Due to Gravity: The acceleration due to gravity (g) is a constant near the Earth's surface, approximately 9.8 m/s². This means that every object, regardless of its mass or size, will accelerate downwards at this rate if there's no air resistance.

* Newton's Second Law: This law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (a = F/m). Since the gravitational force (F) is the same for all objects near the Earth's surface, the acceleration (a) will also be the same.

The Famous Experiment: The famous experiment of dropping a feather and a hammer on the moon (where there's no air resistance) perfectly demonstrates this principle. Both objects fall at the same rate and hit the surface simultaneously.

Air Resistance: While gravity is the constant factor, air resistance can significantly impact the speed and trajectory of objects falling through the atmosphere. Heavier objects with a smaller surface area experience less air resistance, making them fall faster than lighter objects with a larger surface area.

Let me know if you have any other physics questions!