Free fall is a type of motion where ONLY gravitational force is acting upron the object. Be more specific, the velocity of the object has an acceleration of approximately 9.8 m/ s2  on Earth. Free fall also applies to objects that are initially moving upward because at that time gravitational force is also the only force that is acting upon it, while the velocity has a opposite sign ("+" or "-" depends on which on how you look at that) compared  to the object that is moving downwards. Free fall does not specify the sign of velocity, right? That is why this works.      In middle school or high school, most of the time when we see questions about free fall, we will see something in paranthesis at the end of the question like this -- Air resistance is ignmored.  This is because for real free fall, there shouldn't be any air resistance. That is because air resistance is a force that goes in opposite direction with gravitational force when the object falling downwards and in same direction with gravitational force when the object is initially moving upwards!!! To make things easy, middle school or high school just ignore the effect of air resistance. Actually it is impossible to have no air resistance on Earth without special equipment that can pump out all the air in a room. Air reistance will eventually terminate acceleration and make the object move at constant velocity because of friction in the air. That constant speed is called terminal velocity. But sicne this is not related to the real free fall, I am not going to go further on this topic.