Hydro-static pressure is defined as which of the following?

• A. Pressure in a moving fluid due to flow
• B. Pressure in a gas at high temperature
• C. Pressure caused by stirring a liquid
• D. Pressure exerted by a stationary column of liquid due to gravity

Answer: (D)

Hydrostatic pressure is the pressure inside a fluid at rest that comes from the weight of the liquid above a point, caused by gravity. It increases with depth and acts equally in all directions, depending on the liquid’s density and the gravitational field (P = ρgh for depth h). This concept applies only when the fluid isn’t moving; if the fluid flows, you also get dynamic pressure from the motion, which is separate from hydrostatic pressure. Stirring a liquid or any movement introduces those dynamic effects, not just gravity-driven weight. Pressure in a gas at high temperature isn’t defined by a stationary column of liquid, so it doesn’t describe hydrostatic pressure. Therefore, the correct description is pressure exerted by a stationary column of liquid due to gravity.