Activities
    
    
      - 
        Drag the red mass to impart an initial velocity, and see how the 
        system evolves.
      
 
      - 
        Observe what happens when you do the same, but with gravity switched 
        on.
      
 
      - 
        Try changing the relative mass of the blue ball, and notice how the 
        centre of gravity shifts.
      
 
      - 
        Try varying the spring constant and/or the damping coefficient while 
        the simulation runs.