1. Gravity: This is the primary force acting on the object, pulling it downwards. The strength of gravity varies slightly depending on location, but on Earth, it's roughly 9.8 m/s².

2. Air Resistance (Drag): As an object falls, it encounters resistance from the air. This resistance increases with the object's speed and surface area.

3. Initial Velocity: If the object is given a starting push, this initial velocity will affect its speed as it falls.

4. Mass: While mass doesn't directly affect the *acceleration* due to gravity (all objects fall at the same rate in a vacuum), it can indirectly affect the speed. A heavier object will have more inertia, meaning it takes more force to change its velocity. This can lead to a heavier object reaching a higher terminal velocity.

5. Shape and Surface Area: The shape and surface area of an object greatly influence the air resistance it experiences. A wider or flatter object will encounter more air resistance than a streamlined one, slowing its descent.

Terminal Velocity: As an object falls, its speed increases until it reaches a point where the force of gravity is balanced by the force of air resistance. At this point, the object stops accelerating and falls at a constant speed called terminal velocity.

In Summary:

* Without air resistance: The speed of a falling object would increase constantly due to gravity.

* With air resistance: The speed of a falling object will increase until it reaches terminal velocity, where the force of air resistance balances the force of gravity.

Let me know if you'd like a more detailed explanation of any of these factors!