Slow in Slow out

Slow in Slow out

Here is an example of slow in and slow out notice how when the ball reaches the top you get a feeling of inertia, as it swings down hitting the balls in a rhythmic pattern. Using the Graph editor you can create slow in and out using splines

Notice how on this example the slow out is a steep sloping ramp that accelerates down to the hold position. The end of the curve has a straighter line that represents the weight. Overall the only critique for this would be that providing some cushioning could add more weight to the impact. This would mean adding an extra frame as the ball contacts the surface.