Surface Tension of Water

October 25, 2015


PhotographerPhil Lachman
Summary Authors: Phil Lachman; Jim Foster

October  2015 Viewer's ChoiceWhen the drop of water featured above meets the surface of a pool of water it doesn’t immediately sink into it. For a brief moment after contacting the water's surface the drop is still intact and pushes the surface downward. Surface tension, which is due to the cohesive force between water molecules, is responsible for this phenomenon. This drop was captured at the point where the cohesive forces between the water molecules in the drop and the cohesive forces between the water molecules in the pool are still separate.

Water molecules are bent in such a way that the oxygen side has a slight negative charge while the side with the hydrogen atoms has a slight positive charge. This bipolar nature of water molecules gives water its cohesive nature, and thus, its stickiness and it's ability to clump. It's untrue that a skin forms on the water surface. Rather, the stronger cohesion between the water molecules as opposed to the attraction of the water molecules to the air makes it slightly more difficult to move an object through the surface than to move it when it is completely submerged. Note the caustic network here -- bright and dark patterns beneath the surface. Photo taken on November 21, 2010.

Photo Details: Camera Model: Canon EOS 50D; Lens: EF28-135mm f/3.5-5.6 IS USM; Focal Length: 120.0mm; Aperture: ƒ/5.6; Exposure Time: 0.0005 s (1/2000); ISO equiv: 800.