Here's why:
* Pressure is a scalar quantity: Pressure doesn't have a direction, it's just a measure of force per unit area.
* Fluids exert pressure equally in all directions: This is a fundamental property of fluids. Imagine a small, flat surface submerged in a fluid. The molecules of the fluid bombard this surface from all sides, resulting in a net force that is perpendicular to the surface.
However, there are situations where the *force* exerted by a fluid might not be perpendicular to the surface:
* Fluid flow: When a fluid is flowing, there's a component of force parallel to the surface due to friction between the fluid and the object. This is called viscous force.
* Buoyancy: While the pressure itself is perpendicular, the net force due to buoyancy is upward (opposite to gravity) because the pressure at the bottom of the object is greater than the pressure at the top.
In summary: Pressure itself is always perpendicular, but the resulting force might have components that are not perpendicular due to fluid flow or other factors.
