void function ( ) { vy = - vy ; count ++ ; }
updates the velocity of this particle upon collision with a horizontal wall by reflecting the velocity in the y-direction . assumes that the particle is colliding with a horizontal wall at this instant . concode_field_sep double vx concode_elem_sep double vy concode_elem_sep Color color concode_elem_sep double INFINITY concode_elem_sep double rx concode_elem_sep double ry concode_elem_sep double mass concode_elem_sep int count concode_elem_sep double radius concode_field_sep double kineticEnergy concode_elem_sep void move concode_elem_sep void bounceOff concode_elem_sep void bounceOffVerticalWall concode_elem_sep int count concode_elem_sep double timeToHit concode_elem_sep void draw concode_elem_sep double timeToHitVerticalWall concode_elem_sep double timeToHitHorizontalWall