Water and paper clip

Introduction

Surface tension is a fundamental property of liquids. It causes liquids to curve into the smallest possible specific surface area (sphere), if they are not subjected to external forces. The cause of surface tension is the cohesive force between the particles of the liquid (atoms, simple and complex ions, molecules, or small aggregates of these). Hence the spherical shape of a small floating liquid droplet, or a soap bubble.
It is the consequence of surface tension that certain objects and animals do not sink in water, but remain on the surface, even though their density is greater than that of the liquid.

One of the most common forms of water pollution is the release of detergents into living water. (Detergents can be for example washing up liquids, washing powders or capsules. All these reduce the surface tension of water.) If a detergent changes the surface tension of water, many other features of the water surface are also altered, adversely affecting the habitat of the plants and animals that live there.

Objectives

• To familiarize students with the concept of surface tension
• To experiment with surface tension
• To experience the effect of detergents on surface tension

Learning outcomes

By the end of this learning scenario, students will be able to:

• understand the concept of surface tension
• understand that detergents change the surface tension of water
• the change of the surface tension of water has a dramatic
consequence on the life or aquatic creatures