Final answer:
Pressure in one part of a confined fluid is increased, Pascal's Principle states that this increase is transmitted undiminished to all portions of the fluid and to the container's walls, leading to a uniform increase in pressure throughout the fluid.
Step-by-step explanation:
When pressure is applied to one part of a confined fluid, according to Pascal's Principle, this pressure is transmitted undiminished to every other part of the fluid, as well as to the walls of its container. This is because the pressure is defined as force per unit area, and an enclosed fluid cannot flow away to relieve the pressure. If additional weight Mg is added to a piston on top of an enclosed fluid, this increases the pressure at the top and bottom by Mg/A, as the same change in pressure is transmitted throughout the fluid.
Therefore, when pressure in one part of a confined fluid is increased, the pressure everywhere increases by the same amount. This is different from an open fluid system, like a river, where the fluid can flow away, making it difficult to increase the pressure by pushing on it directly.