Use the Easy Ease command on the keyframes to ramp position property up & down. Adjust it using the graph editor. Motion track any iPad movements, probably in Mocha. Use rotobrush to isolate finger on a layer above the original video.
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA
Are you trying to match the finger movement and "inertia" effect as the screen scrolls to a stop? What Dave's suggesting is basically the best way to go about it. Are you familiar with the graph editor? I'd take some time to get to know it and really learn it, otherwise you might try a script like Keysmith that lets you plug in the numbers for influence and velocity, among other things.
Still, learn the graph editor. It's the bane of most motion designer's existence. Once you get over that, you'll enjoy keyframing in AE much more.