Question

A steel blade float on the surface of pure water when detergent is added,it sinks.why?

Answer 1

When a steel blade is placed on water horizontally, the surface tension and the buoyancy will be able to balance the wight of the blade and it will float on the water surface. You know the buoyancy is not sufficient to make the steel blade float. Now if you add detergent to water, the surface tension of water immediately decreases. The surface tension no longer be able to balance the blade and it will sink.