A ball is rolling across the floor. How could you apply an unbalanced force to change the speed or direction of the ball?

Kick the ball! The force of the kick likely isn't the same amount of force acting on the ball as it's rolling, so as long as the kick makes the ball go faster (or slower) than it had been, that force is unbalanced

Usually a ball would roll toward the side that's lower, so if you had a ramp and put it on the side that was lower, then the ball would change direction and go the opposite direction