Actually the space station is always falling but never hitting the ground. Due to inertia, a moving object continues moving in a straight line unless a force acts on it. There is a force that acts on every object near Earth, the force of gravity. For ex. if you throw a ball, it does not continue moving indefinitely in a straight line because gravity causes it to move toward the center of the Earth. In a few seconds, the ball collides with Earth and the force of friction stops its motion.
