 This is a simple demonstration you can do at home to show the independence of vertical and horizontal motion. All you need for it is a tabletop and two pennies or two coins of any kind. Place one coin right on the edge of the table so it's just teetering. And place the other coin. What you're going to do with the other coin is flip it with your finger so that it just grazes the first one and the first one will drop at the same time that the second one is projected off the table. The question is when will they hit? Which one of the coins will hit first or will they hit at the same time? Let's go ahead and try this and see what happens. Okay, if you were listening to the sound you probably heard only a single sound when they hit. They hit at the same time. Let's do that one more time. Why do they hit at the same time? Even though one coin has to travel a further distance to get to its target, well again it's because the horizontal and vertical motions are independent of each other. The objects fall at the same rate because they are both influenced by the acceleration due to gravity. And because they fall at the same rate and the horizontal motion has no influence, this means that since they fall the same distance they must take the same amount of time. Now it might help to understand why the projected penny falls further than the drop penny in the same amount of time if you think of it like this. At any instant of time the projected penny has a downward velocity component like this and this is due to gravity. Now the drop penny also has the same velocity vector at the same instant of time. However the projected penny also has a horizontal velocity component due to the flip that I gave it initially. The overall velocity vector of the projected penny is therefore diagonal to the two components and has a magnitude that is greater than either of the components. So the average velocity of the projected penny is greater than that of the drop penny. With a greater average velocity the projected penny will obviously travel a greater distance in the same amount of time than the drop penny will.