Terminal veloxity
First of all, gravity is not a force, it is an acceleration. What you mean is the force of weight, which is the acceleration of gravity multiplied by mass (all forces are vectors, and gravity is not a vector.) When air resistance is subtracted from weight, you have the net force on a falling object (assuming those are the only forces acting on it.)
Terminal Velocity
air Resistance is a type of force
At some point the air resitance on an falling object will become equal to the force of gravity and the falliing object will stop acceperating. This is called "terminal Velocity"
Terminal Velocity
Air has no effect on gravity. But the presence of air can change the response of an object to the force of gravity alone.
Since gravity attracts the ball downward, and air resistance acts upwards (assuming that it falls straight down), you need to subtract the force of gravity (i.e., the weight) minus the air resistance.
Gravity and Resistance Under free fall, the only force acting upon an object is the force of gravity. But realistically, there is also the force of friction from the air (Air Resistance) that opposes the force of gravity.
The force that acts on a ball when in the air is gravity.
The idea is to calculate the downward force of gravity, and then subtract the air resistance, since it acts in the opposite way. This assumes that the ball falls directly downward.
The net force on a following object
"Free fall" means that gravity is the only force acting on a body.