Relating Force and Motion

Sixth grade teams set up an investigation regarding force and motion.  Each team dropped a single plastic cube onto the raised end of a ruler and observed how high a single cube was launched. The teams continued dropping cubes (2, 3 , 4, and even 5 cubes) onto the raised end of the ruler and observed how high the single cube was launched.  Each was repeated for a total of 3 trials to give more valid results.  

How was the force related to the motion of a launched cube?  Opposite directions!!!