Orbits and satellites
When an object is projected horizontally, its motion is determined by its initial horizontal speed and the rate at which it falls. In the example of Fig.1, alter the speed with which the ball is fired from the cannon and note the effect on the motion.
In this simple case, the ball falls towards the ground but the curvature of the Earth means that the ground also 'falls away'. When the projection speed is correct, the ball falls towards the ground at the same rate as the ground falls away and so the ball travels parallel to the ground. Consequently, in the absence of other forces, the ball orbits the Earth!