code: function(position, velocity, dt) {
          return mf.add(position, mf.mulScalar(velocity, dt));
        }
docs: calculates the new position by speed and delta-time.
  @method getPositionByVeloAndTime
  @param position {Vector3d} The old position.
  @param velocity {Velocity} The velocity.
  @param dt {Number} The delta-time.
  @return {Vector3d} The new position.
  @for motionpredict