Water also has a strong surface tension. When an iron paper clip is placed carefully on top of the water's surface, it will not sink. Instead, it stays on top of the water's surface (image on the left below). However, even the slightest touch can make the paper clip sink to the bottom of the water, because iron is more dense than water.

The picture on the right below shows how a aluminum disc has pushed the water's surface downwards. It looks like the water's surface contains a thin film that the aluminum disc cannot penetrate. Note that the disc does not float, but instead stays in its place thanks to water's surface tension. This surface tension is caused by water molecules, which cling on to one another more tightly near the water's surface. 


Examples of water's surface tension.

The surface tension effect is so strong that it will make water drops round. The surface on which the drop of water is placed will determine how round the drop will become. On plant leaves, for example, water drops can easily become ball-shaped because of surface tension.

Water's surface tension is so strong that a large amount of water can be poured on top of a coin before it will spill out. 



Water's surface tension creates round drops (on the right) and makes it possible for large amounts of water to stay in small amounts of space (on the right).

Soap also has a strong effect on water's surface tension. When painting with a water color on a plastic surface, the surface tension effect will make the water color form small drops. However, when soap is added to the water color, the result is a thick, even line. In other words, soap reduces the surface tension effect. This is made us of in washing powders and laundry detergents. The soap contained in these products make it possible for water to reach the deepest folds of fabrics, cleaning the clothes completely. 

The pond skater is a small insect that moves on the surface of water with the help of surface tension. Its legs are oily and hairy, which helps to prevent the surface tension from breaking. 


Image on the left: When soap is added into water, its surface tension effect is reduced. The result is an even line. Image on the left: A pond skater moves on the surface of water.