This exhibit shows how, when the pressure is higher on one side of a membrane, larger molecules can be filtered out from smaller ones and a higher concentration of smaller molecules will exist on the side of lower pressure. The visitor is prompted to press the ‘high’ buttons that control rotor speed for both sides. This represents an equal pressure state and they notice that the blue balls are evenly distributed to both sides even though there is some movement across the membrane in both directions. They also notice that the larger red ball, representing the impurity, always stays on the right side, because it can’t fit through the membrane. Then the visitor is prompted to press the ‘low’ button on the left and ‘high’ on the right. The visitor notices after several seconds how most of the blue balls are on the left now. There is still movement across the membrane but always a higher concentration to the left. The red ball still remains on the right side.