DAMPENING_FACTOR = 0.88
 
def hits(self, other):
    if (self == other):
        # I can't collide with myself.
        return False
    else:
        # Determine if I overlap with the target particle.
        return (self._radius + other.get_radius()) >= distance(self._x, self._y, other.get_x(), other.get_y())
        
 
def bounce(self, target):
    ''' This method modifies this Particle object's velocities based on its
        collision with the given target particle. It modifies both the magnitude
        and the direction of the velocities based on the interacting magnitude
        and direction of particles. It only changes the velocities of this
        object; an additional call to bounce() on the other particle is required
        to implement a complete bounce interaction.
  
        The collision algorithm is based on a similar algorithm published by K.
        Terzidis, Algorithms for Visual Design.
  
        target  the other particle
     '''
    if self.hits(target):
        angle = math.atan2(target.get_y() - self._y, target.get_x() - self._x)
        targetX = self._x + math.cos(angle) * (self._radius + target.get_radius())
        targetY = self._y + math.sin(angle) * (self._radius + target.get_radius())
        ax = targetX - target.get_x()
        ay = targetY - target.get_y()
        self._velX = (self._velX - ax) * DAMPENING_FACTOR
        self._velY = (self._velY - ay) * DAMPENING_FACTOR