CAPILLARY ATTRACTION
Editor’s Note: In this piece Caroline Arena (‘19) explores the forces involved in capillary attraction.
Put a glass tube in a bowl of water and the water will rise in the tube to a height much greater than the surface level of the water in the bowl, seemingly in defiance of the laws of gravity. How can that be, you ask? The answer is capillary attraction -- a process that explains many common, daily occurrences, such as the way that plants absorb nutrients in the ground or the manner in which a paper towel soaks up spilled water. The secret to capillary attraction relates to the interplay between two forces –- cohesion and adhesion. Cohesive forces are responsible for water’s surface tension. The hydrogen molecules at the surface of water cling to one another, and keep water from spreading out indefinitely. Think of a group hug where the people on the outside keep trying to force their way into the middle of the group. Adhesive forces sound similar to cohesive forces, but are entirely different. Adhesion is the attraction of one kind of molecule for another entirely different kind of molecule. Hydrogen molecules in water “like” each other (cohesion), but there are other types of molecules that hydrogen molecules “like” even more (adhesion). For instance, hydrogen molecules in water love to bond with oxygen molecules on the surface of glass, which explains why water will creep up a glass tube until the pull of gravity becomes too great.
Although most of us spend little time thinking about capillary attraction, it is a remarkable process. Ever wonder how water travels from the base of a redwood to the tree’s uppermost leaves more than 300 feet above the ground? The answer is capillary attraction. The trunk of a redwood tree contains millions of small tubes called “xylem,” each of which is made up of cells to which water molecules like to stick. As water evaporates from the leaves of a redwood, the evaporating water molecules start a suction pull of the water around it. This creates a chain reaction in which each cell in the xylem tube pulls up water from the cell beneath it, all the way to the ground, just as a paper towel soaks up water. The reason that redwoods are narrower at their top than at their base is that at some point gravity starts to equal the force of capillary attraction, and the water molecules in the redwood’s xylem tubes cannot ascend any higher above the ground. The forces of cohesion and adhesion, while crucial to an understanding of capillary attraction, also appear to have relevance outside the realm of science.
People often have a natural tendency to associate with others who share similar interests and come from similar backgrounds. In this sense, people are susceptible to cohesive forces. But, people also enrich themselves when they associate with, and are attracted to, others from different backgrounds and with diverse interests. Forming adhesive bonds with others unlike oneself can often be more powerful and rewarding than resigning oneself to the monotony and sameness of a cohesive group of the like-minded. Just as capillary attraction is crucial to sustaining the life of a redwood, forming adhesive relationships with people different from oneself is critical to a person’s well-being and to the health of the community.
Works Cited
Capillarity and gravity. (n.d.). Retrieved April 02, 2017,from http://web.mit.edu/nnf/education/wettability/gravity.html.
Trees & Capillary Action. (n.d.). Retrieved April 02, 2017, from http://www.davidlnelson.md/Cazadero/Trees&CapillaryAction.htm.
Tree Physics 1: capillary action, the height of trees, and the optimal placement of branches. (2008, August 05). Retrieved April 02, 2017, from https://npand.wordpress.com/2008/08/05/tree-physics-1/.
Although most of us spend little time thinking about capillary attraction, it is a remarkable process. Ever wonder how water travels from the base of a redwood to the tree’s uppermost leaves more than 300 feet above the ground? The answer is capillary attraction. The trunk of a redwood tree contains millions of small tubes called “xylem,” each of which is made up of cells to which water molecules like to stick. As water evaporates from the leaves of a redwood, the evaporating water molecules start a suction pull of the water around it. This creates a chain reaction in which each cell in the xylem tube pulls up water from the cell beneath it, all the way to the ground, just as a paper towel soaks up water. The reason that redwoods are narrower at their top than at their base is that at some point gravity starts to equal the force of capillary attraction, and the water molecules in the redwood’s xylem tubes cannot ascend any higher above the ground. The forces of cohesion and adhesion, while crucial to an understanding of capillary attraction, also appear to have relevance outside the realm of science.
People often have a natural tendency to associate with others who share similar interests and come from similar backgrounds. In this sense, people are susceptible to cohesive forces. But, people also enrich themselves when they associate with, and are attracted to, others from different backgrounds and with diverse interests. Forming adhesive bonds with others unlike oneself can often be more powerful and rewarding than resigning oneself to the monotony and sameness of a cohesive group of the like-minded. Just as capillary attraction is crucial to sustaining the life of a redwood, forming adhesive relationships with people different from oneself is critical to a person’s well-being and to the health of the community.
Works Cited
Capillarity and gravity. (n.d.). Retrieved April 02, 2017,from http://web.mit.edu/nnf/education/wettability/gravity.html.
Trees & Capillary Action. (n.d.). Retrieved April 02, 2017, from http://www.davidlnelson.md/Cazadero/Trees&CapillaryAction.htm.
Tree Physics 1: capillary action, the height of trees, and the optimal placement of branches. (2008, August 05). Retrieved April 02, 2017, from https://npand.wordpress.com/2008/08/05/tree-physics-1/.
