パスカルの法則

Pascal's principle states that a pressure change in a confined fluid is transmitted undiminished throughout the entire fluid and to the container walls. When you press a piston on a water gun, the pressure change spreads equally to all nozzles, releasing water at the same pressure from each opening. This occurs because fluid atoms move freely and transmit pressure uniformly in all directions.

Adding weight to a piston increases pressure at the top by the weight divided by the piston's area. According to Pascal's principle, this pressure increase transmits undiminished to all points in the fluid, including the bottom. The total pressure at the bottom becomes the sum of atmospheric pressure, fluid pressure, and the pressure supplied by the added mass.

When water is added to a full barrel, the pressure from the entering water increases rapidly throughout the barrel's volume. According to Pascal's principle, this pressure change transmits undiminished to all points, including the container walls. The increased pressure forces water to leak from all sides equally rather than from a single location.

Pascal's principle applies to pressure changes, not absolute pressure uniformity. Pressure in a static fluid varies with depth because it depends on both the fluid column weight and atmospheric pressure. The principle states that any change in applied pressure transmits undiminished throughout, but the baseline pressure still increases with depth due to gravitational effects.

For a fluid in static equilibrium, the net force on any fluid part must be zero, preventing flow. Pascal's principle explains that pressure changes in this equilibrium state transmit undiminished throughout the fluid. This uniform pressure transmission maintains the equilibrium condition, ensuring the fluid remains stationary rather than accelerating or flowing.

Pascal's principle implies that total pressure at any point equals the sum of pressures from all sources acting on the fluid. For example, pressure at a specific depth includes atmospheric pressure from above, pressure from the fluid column weight, and any additional applied pressure. Each source contributes independently to the total pressure experienced at that location.

In an enclosed fluid, atoms move freely and transmit pressure to all parts uniformly. When pressure is applied at one point, it spreads equally throughout because the fluid cannot escape. This undiminished transmission occurs regardless of container shape or size, making Pascal's principle fundamental to hydraulic systems and pressure-based applications.