Babies close to the age of one continue to dramatically increase their motor skills and brain activity, this increase creates a new level of playing.  With their touch and taste senses still going ballistic, they are now interested in reactions.  The reaction your baby causes by  dropping, throwing, or knocking something down teaches them about cause and effect and each time they do one of these activities which they may do over and again, they learn how to do it better.  The main lesson they will learn; is that they can make things happen.  This creates a strong sense of independence and empowerment.  Babies starts to realize the control they have over their environment, they are now able to choose where things go.  This can be a difficult stage, but it is a milestone for development.