Adhesion and Cohesion of Water

Water drops on pine needles, showing the effects

of gravity, adhesion, and cohesion on water.

I used to wake up in a cold sweat in the middle of the night because I could not get the concepts of water adhesion and cohesion clear in my mind. If you have that problem, too, then do yourself a favor and read on to learn about these important properties of water.

Cohesion: Water is attracted to water

Adhesion: Water is attracted to other substances

Adhesion and cohesion are water properties that affect every water molecule on earth and also the interaction of water molecules with molecules of other substances. Essentially, cohesion and adhesion are the "stickiness" that water molecules have for each other and for other substances. You can see this in the picture to the right.

 The water drop is composed of water molecules that like to stick together, an example of the property of cohesion. The water drop is stuck to the end of the pine needles, which is an example of the property of adhesion. Notice I also threw in the all-important property of gravity, which is causing the water drops to roll along the pine needle, attempting to fall downwards. It is lucky for the drops that adhesion is holding them, at least for now, to the pine needle.