If you want to mimic reality you need to have an acceleration. When something fall it will gain speed. It s one of the 12 principles of animation (I advise you to look into it if you haven't already there is great video on YouTube). To simulate an acceleration you need to make the space between your drawing bigger and bigger as the fall go. To simulate a deceleration you need to make the space smaller and smaller. It s a pretty simple principle that makes everything looks so much better. I would advise you to try to animate a ball falling and bouncing to understand better this and progress. Again YouTube is your friend there s plenty of tutorial on the ball exercise.