Plant Physiology – code: 7810.01

Capillarity is one of the causes for the upward flow of water in the soil and in plants. This phenomenon can be observed as a spontaneous movement of liquids up or down narrow tubes, or capillaries. It can be seen, for example, when the surface of water in a clean drinking glass is slightly higher at the edges, where it is in contact with the glass, than in the middle thus forming a concave meniscus. The molecular interaction between the liquid and the tube, or glass, are responsible for this phenomenon. In fact, if the force of attraction between the material of the tube and the liquid is stronger than the force of attraction between the liquid molecules, the liquid tends to rise in the capillary. On the contrary, if the force of attraction between the liquid molecules is stronger than the attraction between the liquid and the material of the tube, the liquid will fall.

Naturally, the force of gravity also plays a role in the whole process by balancing the force that pulls the water up. In this experience we will see how the dimensions of the tubes influence the level of the water. The capillarity apparatus demonstrates how narrow tubes of different gauges cause different liquid levels.