The independent variable is the factor that is intentionally changed or manipulated by the experimenter. The dependent variable is the factor that is measured and observed, and it changes in response to the independent variable. In the given research question: "the relation of flow of water and rotation of the knob of the tap": The rotation of the knob of the tap* is what is being changed or controlled. The flow of water* is what is being observed and measured as a result of changing the knob's rotation. Therefore, the independent variable is the rotation of the knob of the tap. The independent variable is the rotation of the knob of the tap.