Which principle states that the internal forces within a fluid are transmitted equally in all directions?

The principle that states that the internal forces within a fluid are transmitted equally in all directions is Pascal’s principle. This principle is foundational in fluid mechanics and is vital in understanding how pressure works in fluids. It asserts that when pressure is applied to a confined fluid, that pressure change occurs uniformly throughout the fluid, ensuring that every part feels the same pressure increase.

This property is exploited in many hydraulic systems, such as hydraulic lifts and brakes, where a small force applied to a small piston can create a larger force at another piston due to the equal transmission of pressure in the fluid.

Understanding Pascal's principle is crucial for anyone studying mechanics, as it helps to explain how forces are transferred in various applications involving fluids, making it a cornerstone concept in the field.