Zipping Action due to Cohesive Force
By Jitender Singh
To study the cohesive and adhesive forces with the help of newspaper.
Procedure
Cut two paper strips, about 2 cm wide along the length of a newspaper and wet them. Hold the wet strips about 3 cm apart, hanging parallel to each other. Ask your friend to join the lower ends of the strips together. Soon the strips will stick all the way to the top, like zipping of a zipper (except near the upper ends).
Discussion
Water molecules have a property of sticking to one another (called cohesion) and also to molecules of other materials (called adhesion). Paper gets wet due to adhesive property of water. When you bring the bottom ends together, due to cohesive property, water molecules at the bottom of two strips cling together. In turn, water molecules just above them come closer and they also cling. This process continues all the way to the top.
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