Capillary Equilibrium Tube

Product Details

The results of this demonstration will require some thoughtful explanation because the final water levels are not all the same height as one might predict. Normally water in a series of commonly connected tubes at the same height would all reach equilibrium due to equal air pressure on the columns. But in this demonstration, the diameter of some of the tubes is so small that the force of capillary action pulling up on the water is greater than the air pressure above the water, thus pulling the water even higher. Since the force of capillary action is essentially constant for a particular liquid, the cross-sectional area of the tube is the determining factor for the final height of the water. The four tubes and reservoir form a single all-glass unit that is held upright in its enclosed stand. Detailed exploration of capillary force is included.