Water is sticky and clumps together into drops because of its cohesive properties, but chemistry and electricity are involved at a more detailed level to make this possible. Water is highly cohesive-it is the highest of the non-metallic liquids. Sources/Usage: Some content may have restrictions. Although you may have heard of a "skin" where water meets the air, this is not really an accurate description, as there is nothing other than water in the drop. On Earth, the effect of gravity flattens this ideal sphere into the drop shape we see. For water, this state happens when a water molecule is surrounded on all sides by other water molecules, which creates a sphere or ball (perfectly round if it was in outer space). The natural form of a water drop occurs during the "lowest energy state", the state where the atoms in the molecule are using the least amount of energy. It turns out that this surface tension is the result of the tendency of water molecules to attract one another. If you just look at the picture of the water drop sitting of the leaf, you might think the water drop has a "skin" holding it into a sort of flattened sphere (although there is nothing flat about a water drop in outer space). Adhesion and cohesion are winning the battle so far, as the drops are sticking to the pine needles. Gravity is working against both adhesion and cohesion, trying to pull the water drop downward. Also noticeable in this picture is the effect that gravity has on the water drops. In the picture of pine needles above, the water droplets are stuck to the end of the pine needles-an example of the property of adhesion.
Schmidt, National Park ServiceĪ water drop is composed of water molecules that like to stick together-an example of the property of cohesion.