Question

A steel blade floats on the surface of pour water, when detergent is added it sinks. Why?

Answer 1

Hint We know that the Archimedes principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged and is equal to the weight of the fluid that the body displaces and acts in the upward direction at the centre of mass of the displayed fluid. Based on this concept solve this question.

Complete step by step answer:
We know that when a steel blade is placed on water horizontally, the surface tension and the buoyancy will be able to balance the weight of the blade and it will float on the water surface. We know the buoyancy is not sufficient to make the steel blade float.
Now, if we add detergent to water, the surface tension of water immediately decreases. The surface tension no longer is able to balance the blade and it will sink.
Hence, the steel blade floats on the surface of pour water, when detergent is added it sinks.

Note We know that buoyancy is caused because of the differences in pressure acting on opposite sides of an object immersed in a static fluid. It is also known as the buoyant force. The upward force that is applied by the fluid on the object or the body when an object is put in or submerged in the fluid.