Final answer:
In air, a dropped ball experiences gravitational and air resistance forces. In a vacuum, only gravitational force acts on the ball.
Step-by-step explanation:
In air, when a ball is dropped, two forces act on the object: gravitational force and air resistance force. The gravitational force pulls the ball towards the ground, while the air resistance force opposes the motion of the ball through the air.
In a vacuum, such as outer space, only the gravitational force acts on the ball. Since there is no air or atmosphere, there is no air resistance force.