Competency #1
Answer and Explanation
Free fall is defined as the motion of an object that is only being acted on by gravity. That means the only force acting on the object is the force of gravity.
Free fall is possible when either there is no air resistance or so little that it is insignificant. When can this happen?
Either the object is moving in a place that has no air (e.g. the moon). The moon travels around the earth, with the only force acting on it being the gravitational attraction from the earth. Thus, we can say the moon is in a constant state of free fall.
Objects on the Earth can also be described as in free fall, but only under some special circumstances. Air resistance depends on speed of motion. When objects first begin to fall, they have not had time to accelerate much, so they are initially falling slowly. Thus, the air resistance is negligible, and we can say they are experiencing free fall. This is true for a baseball and a piece of crumpled paper dropped from a height of 4 feet. If there was significant air resistance, the baseball would hit the ground first. However, both hit at the same time, indicating that air resistance is insignificant on both objects.
The force diagram for an object in free fall looks like this:
