class PhysicsObject{
  float radius,mass,friction;
  float x,y,z;
  float fx,fy,fz;
  float vx,vy,vz;
  PhysicsObject next;
  void simulate(){
  }
  void ballInteraction(PhysicsObject po){
  }
  void surfaceInteraction(PhysicsObject po){
  }
  void clothInteraction(PhysicsObject po){
  }
  void gravityInteraction(PhysicsObject po){
  }
  void frictionInteraction(PhysicsObject po){
  }
  void update(){
  }
  void visualize(){
  }
  void add(PhysicsObject po){
    if(next==null){
      next = po;
    } 
    else {
      next.add(po);
    }
  }
}
//##################################################

//##################################################
class Surface extends PhysicsObject{
  Surface(float iy){
    y = iy;
    friction = 0.8;
  } 
  //------------------------------------------------
  void simulate(){
    PhysicsObject obj = objects;
    while(obj!=null){
      if(obj!=this) obj.surfaceInteraction(this);
      obj = obj.next;
    }
    if(next!=null) next.simulate();
  }
}
//##################################################
class Gravity extends PhysicsObject{
  float force;
  Gravity(float igrav){
    force = igrav;
  }
  //------------------------------------------------
  void simulate(){
    PhysicsObject obj = objects;
    while(obj!=null){
      if(obj!=this) obj.gravityInteraction(this);
      obj = obj.next;
    }
    if(next!=null) next.simulate();
  }
}
//##################################################
class Friction extends PhysicsObject{
  Friction(float ifriction){
    friction = ifriction;
  }
  //------------------------------------------------
  void simulate(){
    PhysicsObject obj = objects;
    while(obj!=null){
      if(obj!=this) obj.frictionInteraction(this);
      obj = obj.next;
    }
    if(next!=null) next.simulate();
  }
}
//##################################################