The air resistance of an object is proportional to the object's velocity, and the surface area of the object that is in contact with the air. If a feather and a golf ball are dropped at the same time...
In the absence of air resistance, the force of gravity has no effect on the horizontal component of a projectile's velocity, and causes the vertical component of its velocity to increase by 9.8...
The horizontal component of velocity for a projectile is not affected by the vertical component at all. Horizontal component is measured as xcos(theta)Vertical component is measured...