Final answer:
Paper and cork float on water due to their low density, which is less than that of water. Besides density, surface tension due to water's cohesive forces also plays a role in keeping light objects afloat on water.
Step-by-step explanation:
Paper and cork float on water because they have low density. Objects or substances that have a lower density than the fluid they are in tend to float due to the buoyant force exerted on them. For instance, oil floats on water, a hot-air balloon floats in the atmosphere, and a bit of cork can float in wine.
This principle is also why icebergs float in the ocean. In addition to density, the phenomenon of surface tension also plays a crucial role in allowing objects to float. This is seen when a small paper clip or a needle is placed gently on the surface of water and it doesn't sink due to the cohesion of water molecules forming a 'skin' at the surface, strong enough to hold light objects without breaking.