In this chapter we will investigate a pin floating on the surface of a liquid due to surface tension. Cohesive forces among liquid molecules close to the surface of a liquid cause the surface tension phenomenon. The surface molecules of a liquid do not have similar molecules above them. As a result, these surface molecules exert greater cohesive forces on the same molecules below the surface and on those next to them on the surface. These excessive cohesive forces of the surface molecules have a tendency to contract to form a membrane-like surface and minimize their excess surface energy. Let us formulate the forces acting on a round pin with length L (m), diameter D (m), and density ρpin (kg m−3) floating on the surface of a liquid, as shown in Figure 8.1.