type
  TParticle = class(TObject)
  private
    x_, y_, dx_, dy_, vx_, vy_: Single;
  public
    property x: single read x_ write x_;
    property y: single read y_ write y_;
    property dx: single read dx_ write dx_;
    property dy: single read dy_ write dy_;
    property vx: single read vx_ write vx_;
    property vy: single read vy_ write vy_;
    constructor Create(_x, _y, _dx, _dy, _vx, _vy: single);
  end;

  TJoint = class(TObject)
  private
    a_, b_: integer;
    Length_: Single;
  public
    property A: Integer read a_ write a_;
    property B: Integer read b_ write b_;
    property Length: Single read Length_ write Length_;
    constructor Create(FirstNode, SecondNode: integer; len: single);
  end;

  TParticleList = class(TObjectList)
  private
    function GetItem(Index: Integer): TParticle;
  public
    function Add(AObject: TParticle): Integer;
    property Items[Index: Integer]: TParticle read GetItem; default;
  end;

  TJointList = class(TObjectList)
  private
    function GetItem(Index: Integer): TJoint;
  public
    function Add(AObject: TJoint): Integer;
    property Items[Index: Integer]: TJoint read GetItem; default;
  end;