Question

Why is force exerted by static fluids always perpendicular to a surface?

Short answer

Parallel components of force cause flow of the fluid.Therefore only perpendicular component of force exist.

Step-by-step solution

Defining static fluid

Static fluid is the fluid in which flow is restricted. Pressure is applied uniformly on all surfaces. But the applied force is always directed perpendicular to the surface.

Explaining the reason behind the perpendicular force in static fluid

Consider a body immersed in a container with liquid. According to Newton’s third law, if a parallel force is applied to the object, it will produce a pressure gradienton the surface of fluid. The fluids, due to there ability to flow, will settle themselves accordingly. Thus, force exerted by static fluids are only perpendicular to the surface.Since flow is not possible in this scenario.

Hence, the force applied to the surface will be perpendicular to the surface.