Final answer:
Cohesion and surface tension allow water to hold up materials that are heavier than itself.
Step-by-step explanation:
Cohesion allows for surface tension and holds molecules together at the surface of a bulk sample of water, creating a 'skin' like effect. This property allows objects that are denser than water, such as steel or paper clips, to float on the surface of water. The surface tension created by cohesive forces keeps the water molecules intact and supports the object floating on top.