Physics 4 — Thermo & Fluids

Fluids at rest — pressure & buoyancy

continues from lesson 3 — values defined earlier in the course stay live here

Depth is weight: P = ρ·g·h stacks a column of fluid on you. Every 10 m of water adds about one atmosphere:

\rho _{w} := 1000 kg/m^3

= 1000 kg / m^3 water density

g := 9.81 m/s^2

= 9.81 m / s^2

P_{30m} := \rho _{w} * g * 30 m

= 294300 Pa gauge pressure at 30 m — about 3 atm

Archimedes: the water you displace pushes back with its own weight. A 70 kg swimmer displacing 68 liters — do they float?

m_{sw} := 70 kg

= 70 kg

V_{disp} := 0.068 m^3

= 0.068 m^3 displaced volume, lungs full

F_{buoy} := \rho _{w} * g * V_{disp}

= 667.08 N buoyant force

✓ pass

F_{buoy} < m_{sw} * g

lungs full ≈ neutral: this swimmer sinks SLOWLY (try 0.072 m³)