Hydrostatic pressure is defined as pressure exerted by a fluid at rest due to gravity. How does it change with depth?

• A. Hydrostatic pressure increases with depth.
• B. Hydrostatic pressure is caused by surface tension.
• C. Hydrostatic pressure decreases with depth.
• D. Hydrostatic pressure stays constant with depth.

Answer: (A)

Pressure in a fluid at rest increases with depth because every layer of fluid above adds its weight to the pressure felt below. The relationship is P = P0 + ρ g h, where P0 is the surface pressure, ρ is density, g is gravity, and h is depth. As you go deeper, h grows, so P increases linearly (assuming uniform density).

Surface tension isn’t what sets this bulk pressure change; it mainly affects interfaces and capillary effects, not the steady increase with depth in a large body of fluid.

So the correct idea is that hydrostatic pressure rises with depth, not decreases or stays the same, and not due to surface tension.