Using a tennis racket to hit a tennis ball is a great example of lopsided power following a moving article. When the ball is hit, it flies over the net before being dragged to the ground by gravitational pull. If it weren't for the existence of gravity, the tennis ball would continue to fly in a straight line until the end of time. In tennis, the most obvious case of Newton's first law is the trajectory of the ball. When you hit the ball with the racket, it goes off in a certain direction. If you were playing in the vacuum of intergalactic space, light years from any gravity-creating body, the ball would proceed in that direction quite uncertainly, in light of the fact that no external force would follow it. On Earth, however, two noteworthy forces are disappearing: air resistance moderates the speed of the ball, and gravity pushes the ball toward the ground (Livingstrong,