Fluid Pressure & Buoyancy Calculator

Fluid Pressure Guide

What do I need to know about Pressure in Fluids?

Gauge pressure: P = ρgh. ρ = fluid density (kg/m³), g = 9.81 m/s², h = depth (m). Absolute pressure = P_gauge + P_atm = ρgh + 101,325 Pa. Pressure depends only on depth and fluid density — not on the shape of the container or the surface area. Example: at 10m depth in fresh water (ρ=1000). P = 1000 × 9.81 × 10 = 98,100 Pa = 98.1 kPa. Absolute: 98.1 + 101.3 = 199.4 kPa ≈ 2 atm. Every 10m in water ≈ 1 atm additional pressure. Scuba diving at 30m: approximately 4 atm absolute. Atmospheric pressure at the surface already adds a full atmosphere before any water depth is even considered, which is why total absolute pressure underwater rises faster than people intuitively expect.

What's the key thing to understand about Archimedes Principle?

Buoyancy force = weight of fluid displaced. F_b = ρ_fluid × g × V_submerged. Where V_submerged = volume of the object that is underwater. Example: 0.01 m³ object in seawater (ρ=1025). F_b = 1025 × 9.81 × 0.01 = 100.6 N. If the object weighs less than 100.6N (mass < 10.25kg): it floats. If heavier: it sinks. If exactly 100.6N: neutrally buoyant (submarine hovering). Ships float because the hull shape displaces a large volume of water — even though steel is denser than water, the total average density of the hull's shape, including the air inside, is less than water, which is what allows it to float.

What do I need to know about Floating and Sinking?

Object floats if: ρ_object < ρ_fluid. Object sinks if: ρ_object > ρ_fluid. Neutrally buoyant if: ρ_object = ρ_fluid. When floating: the object displaces its own weight of fluid. Fraction submerged = ρ_object / ρ_fluid. Ice in water: ρ_ice = 917 kg/m³. Fraction submerged = 917/1000 = 0.917. 91.7% of ice is below water — only 8.3% above the surface. Iceberg fraction: 917/1025 = 89.5% submerged in seawater. Human body: average density approximately 985 kg/m³ — just denser than fresh water (sinks),

What's the key thing to understand about Pascal's Law and Hydraulics?

Pascal's Law: a pressure change in an enclosed fluid is transmitted equally to all parts of the fluid. Hydraulic systems: small force applied over small area = large force over large area. F_out/F_in = A_out/A_in. Car hydraulic brakes: small pedal force × small master cylinder area = large force at large brake caliper area. Hydraulic jack: input cylinder 2cm², output 100cm². 1N input → 50N output. Car jack lifts 1 tonne car with 20N of force. Multiplied area ratio: 50,000:1. Hydraulic systems can therefore multiply force dramatically using nothing but fluid pressure and a difference in piston area — no motors or gears required.