 In this demonstration we'll see that the vertical and horizontal motions of a projectile do not influence each other. The projectile that we'll use is this plastic ball and we'll project it with this cannon. This cannon, this device has a spring in it and I'll just hold it here so you can see it. And I can force the spring down and it will stay in place there. So the spring is compressed at this point. I'll push the cart along this level track and my table is not quite level so I put some cardboard here to make sure that it was level. So you can see the cart doesn't move on the track. The other thing that I need is to release the ball and for that purpose I have an automatic release which is a photogate. The photogate is this device on the side which has a slot in it. There's an infrared beam passing across it. If I break that infrared beam with something then that will release the ball. What I'll break it with is this piece of cardboard. So I'm going to mount this cardboard on this clamp right here at exactly the level of the photogate. And double check. Now when I pass it through, let me just show you how this works. When I pass it through the photogate it releases the ball. So I'll get the flag in position, line it up and we're set to go. Ready the cart? I'll give a push and I'll stop pushing before the flag actually passes through the photogate. As you can see the ball fell right back down into the cannon. Let's take another look at that. Ready? Right back down into the cannon before I actually caught it over here. So what that is showing us is that the ball continues traveling horizontally with the same speed that the cart has. The cart doesn't slow down. The ball doesn't slow down. And since they're both moving horizontally together the ball comes right back down in the cart. And the fact that gravity was acted on the ball all the time and making it slow down on the way up and speed up on the way down had absolutely no effect on that horizontal motion.