The factor of gravity that causes objects to change velocity as they move toward Earth is acceleration due to gravity.

Here's why:

* Gravity's Pull: Earth's gravity exerts a force on all objects, pulling them towards its center.

* Acceleration: This force causes the objects to accelerate, meaning their velocity changes over time.

* Constant Acceleration: The acceleration due to gravity near the Earth's surface is approximately 9.8 m/s², which means an object's velocity increases by 9.8 meters per second every second it falls.

In simpler terms: As an object falls towards Earth, gravity pulls it faster and faster. This increasing speed is the result of the object's changing velocity due to the constant acceleration caused by gravity.