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A steel needle or a razor blade can float on water if placed gently due to surface tension, which arises at the interface between a liquid and a gas or two liquids that do not mix.

The surface tension makes the liquid surface behave like a stretched elastic membrane, thereby supporting the object.

Surface tension results from cohesive forces acting among liquid molecules. Molecules within the liquid are surrounded uniformly by other molecules, resulting in balanced forces in all directions.

On the other hand, molecules at the surface experience an unbalanced force toward the liquid's interior, creating a skin effect on the surface.

The intensity of these cohesive forces per unit length is called surface tension. Surface tension varies with temperature and fluid type, decreasing as the temperature increases.

Surface tension is crucial in processes like the formation of droplets. In irrigation systems, water forms droplets that can be evenly distributed over plants.

The cohesive forces within the water help maintain the droplet shape until it contacts a surface, ensuring efficient water usage and distribution.