In this demonstration a small ball will be propelled through a spring loaded launcher towards a metal target. The target is held in place by an electromagnet. When the ball is launched it passes through a photogate, which causes the current
to the magnet to be cut, thus releasing the target, allowing it to free-fall. Let's see what happens.
Why did the ball hit the target? The ball and the target accelerate vertically at the same rate both begin falling at the same instant. In the absence of
gravity the ball would follow a straight line path directly to the target. With gravity, the ball falls vertically away from the straight line. At any instant, the ball and the target have fallen the same vertical distance. Inevitably, they meet. We will now
shoot the ball again. With a slower velocity as it leaves the launcher. The ball still hits the target after falling a greater distance. This shows that the ball's vertical motion is independent of its horizontal motion.