* Free fall is defined as the motion of an object solely under the influence of gravity. No other forces are acting on it (like air resistance).

Let's look at why the other options are incorrect:

* Stationary: An object in free fall is moving, not stationary.

* Decelerating: While gravity can cause deceleration (slowing down) in certain situations (like when an object is thrown upwards), it doesn't necessarily mean the object is decelerating in all cases of free fall.

* Projectile: A projectile is an object launched into the air with some initial velocity. While objects in free fall can be projectiles, free fall is a broader concept that encompasses any object only influenced by gravity, even if it's not launched.

Key takeaway: Free fall specifically refers to the motion of an object where the only force acting on it is gravity.