this.setForce = function(force)
      {
        var i; 
        
        for(i = 0; i < this.pointMasses.length; i++)
        {
          this.pointMasses[i].setForce(force); 
        }
        this.middlePointMass.setForce(force); 
      }
      this.addForce = function(force)
      {
        var i; 
        
        for(i = 0; i < this.pointMasses.length; i++)
        {
          this.pointMasses[i].addForce(force); 
        }
        this.middlePointMass.addForce(force); 
        this.pointMasses[0].addForce(force); 
        this.pointMasses[0].addForce(force); 
        this.pointMasses[0].addForce(force); 
        this.pointMasses[0].addForce(force); 
      }