If something is traveling at 20 m/s constant velocity, is it in equilibrium? if a projectile is launched at a velocity of 20 m/s, is it in equilibrium?

If something is traveling at 20 m/s constant speed AND its direction isn't changing, then its velocity is constant.  Another way to say that is: Its acceleration is zero.  Zero acceleration means zero NET force acting on the object, or a group of BALANCED forces acting on it, also called EQUILIBRIUM.  The required answer is: YES.

If a real projectile is launched, the force of gravity acts on it vertically downward.  There's no upward force acting on it to balance gravity.  Therefore, the forces on the projectile are NOT balanced, there IS a net vertical force on it, and it's NOT in equilibrium.  Too bad.

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.