## Surface Tension

The picture of a pond skater below shows surface tension at work. Surface tension is a force between molecules in the surface of a liquid. It occurs because the molecules in the surface of the liquid attract each other, so if the are forced apart slightly as below by the weight of the pond

skater, there is a net attractive force in the surface tangential to the surface. If the surface becomes curved as in the picture below, it may support a weight. This is illustrated clearly below. The weight of the needle is supported by the vertical components of the surface tension.

Surface tension is actually defined as the force per unit length in a surface needed to hold the surface together:. If the weight of the needle is W, resolve vertically for the needle:

so