Cohesiveness and Tensile Strength - You have all heard of adhesion (the holding together of unlike substances). For example, the adhesion of adhesive tape holds you and the tape together. There is another way of "holding together," called cohesion, or the holding together of like substances. All of you have seen evidence of the cohesiveness of water molecules at one time or another. As you try to sleep, and finally locate the dripping faucet that has been keeping you awake, you notice that for a few moments before it falls, the trickle of water clings to the faucet as it forms a drop. Others have seen water striders run across the surface of a pond. All these phenomena are due to the surface tension of water. The water moisture in our lungs also exerts a surface tension that we must counteract to avoid the collapse of the air sacs in our lungs. Surface tension is a result of the hydrogen bonds that have formed because of the electronegative and electropositive qualities of water molecules.
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Because of these cohesive properties, water also has a remarkable tensile strength in other words it resists being pulled apart. As a matter of fact, under certain conditions the tensile strength of
water exceeds that of steel wire. The cohesiveness and tensile strength of water help to explain how water can rise hundreds of feet from roots to the needles of a giant redwood tree.
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