Now that you have increased the frame rate
for this animation,
you can also calculate the new value that
the margin should change in each frame.
As the preceding chart makes clear,
now that there are 5 frames instead of 2,
and since the top margin value remains
between 0 and 100 throughout the animation,
each frame either increases or decreases
the ball’s top margin value by 25.

Change in margin value between each
  frame = total change in margin / # of frames

In this case, the top margin changes by 100
over 4 frames, so each frame
changes the top margin value by 25.
(Even though there are 5 total frames,
in this example you are reusing one frame for both
the downward and upward motion of the ball, so you
only need to count 4 frames for the margin change.)